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Our Future Is Now - A Climate Change Essay by Francesca Minicozzi, '21

Francesca Minicozzi (class of 2021) is a Writing/Biology major who plans to study medicine after graduation. She wrote this essay on climate change for WR 355/Travel Writing, which she took while studying abroad in Newcastle in spring 2020. Although the coronavirus pandemic curtailed Francesca’s time abroad, her months in Newcastle prompted her to learn more about climate change. Terre Ryan Associate Professor, Writing Department

Our Future Is Now

By Francesca Minicozzi, '21 Writing and Biology Major

 “If you don’t mind me asking, how is the United States preparing for climate change?” my flat mate, Zac, asked me back in March, when we were both still in Newcastle. He and I were accustomed to asking each other about the differences between our home countries; he came from Cambridge, while I originated in Long Island, New York. This was one of our numerous conversations about issues that impact our generation, which we usually discussed while cooking dinner in our communal kitchen. In the moment of our conversation, I did not have as strong an answer for him as I would have liked. Instead, I informed him of the few changes I had witnessed within my home state of New York.

Francesca Minicozzi, '21

Zac’s response was consistent with his normal, diplomatic self. “I have been following the BBC news in terms of the climate crisis for the past few years. The U.K. has been working hard to transition to renewable energy sources. Similar to the United States, here in the United Kingdom we have converted over to solar panels too. My home does not have solar panels, but a lot of our neighbors have switched to solar energy in the past few years.”

“Our two countries are similar, yet so different,” I thought. Our conversation continued as we prepared our meals, with topics ranging from climate change to the upcoming presidential election to Britain’s exit from the European Union. However, I could not shake the fact that I knew so little about a topic so crucial to my generation.

After I abruptly returned home from the United Kingdom because of the global pandemic, my conversation with my flat mate lingered in my mind. Before the coronavirus surpassed climate change headlines, I had seen the number of internet postings regarding protests to protect the planet dramatically increase. Yet the idea of our planet becoming barren and unlivable in a not-so-distant future had previously upset me to the point where a part of me refused to deal with it. After I returned from studying abroad, I decided to educate myself on the climate crisis.

My quest for climate change knowledge required a thorough understanding of the difference between “climate change” and “global warming.” Climate change is defined as “a pattern of change affecting global or regional climate,” based on “average temperature and rainfall measurements” as well as the frequency of extreme weather events. 1   These varied temperature and weather events link back to both natural incidents and human activity. 2   Likewise, the term global warming was coined “to describe climate change caused by humans.” 3   Not only that, but global warming is most recently attributed to an increase in “global average temperature,” mainly due to greenhouse gas emissions produced by humans. 4

I next questioned why the term “climate change” seemed to take over the term “global warming” in the United States. According to Frank Luntz, a leading Republican consultant, the term “global warming” functions as a rather intimidating phrase. During George W. Bush’s first presidential term, Luntz argued in favor of using the less daunting phrase “climate change” in an attempt to overcome the environmental battle amongst Democrats and Republicans. 5   Since President Bush’s term, Luntz remains just one political consultant out of many politicians who has recognized the need to address climate change. In an article from 2019, Luntz proclaimed that political parties aside, the climate crisis affects everyone. Luntz argued that politicians should steer clear of trying to communicate “the complicated science of climate change,” and instead engage voters by explaining how climate change personally impacts citizens with natural disasters such as hurricanes, tornadoes, and forest fires. 6   He even suggested that a shift away from words like “sustainability” would gear Americans towards what they really want: a “cleaner, safer, healthier” environment. 7

The idea of a cleaner and heathier environment remains easier said than done. The Paris Climate Agreement, introduced in 2015, began the United Nations’ “effort to combat global climate change.” 8   This agreement marked a global initiative to “limit global temperature increase in this century to 2 degrees Celsius above preindustrial levels,” while simultaneously “pursuing means to limit the increase to 1.5 degrees.” 9    Every country on earth has joined together in this agreement for the common purpose of saving our planet. 10   So, what could go wrong here? As much as this sounds like a compelling step in the right direction for climate change, President Donald Trump thought otherwise. In June 2017, President Trump announced the withdrawal of the United States from the Paris Agreement with his proclamation of climate change as a “’hoax’ perpetrated by China.” 11   President Trump continued to question the scientific facts behind climate change, remaining an advocate for the expansion of domestic fossil fuel production. 12   He reversed environmental policies implemented by former President Barack Obama to reduce fossil fuel use. 13

Trump’s actions against the Paris Agreement, however, fail to represent the beliefs of Americans as a whole. The majority of American citizens feel passionate about the fight against climate change. To demonstrate their support, some have gone as far as creating initiatives including America’s Pledge and We Are Still In. 14   Although the United States officially exited the Paris Agreement on November 4, 2020, this withdrawal may not survive permanently. 15   According to experts, our new president “could rejoin in as short as a month’s time.” 16   This offers a glimmer of hope.

The Paris Agreement declares that the United States will reduce greenhouse gas emission levels by 26 to 28 percent by the year 2025. 17   As a leader in greenhouse gas emissions, the United States needs to accept the climate crisis for the serious challenge that it presents and work together with other nations. The concept of working coherently with all nations remains rather tricky; however, I remain optimistic. I think we can learn from how other countries have adapted to the increased heating of our planet. During my recent study abroad experience in the United Kingdom, I was struck by Great Britain’s commitment to combating climate change.

Since the United Kingdom joined the Paris Agreement, the country targets a “net-zero” greenhouse gas emission for 2050. 18   This substantial alteration would mark an 80% reduction of greenhouse gases from 1990, if “clear, stable, and well-designed policies are implemented without interruption.” 19   In order to stay on top of reducing emissions, the United Kingdom tracks electricity and car emissions, “size of onshore and offshore wind farms,” amount of homes and “walls insulated, and boilers upgraded,” as well as the development of government policies, including grants for electric vehicles. 20   A strong grip on this data allows the United Kingdom to target necessary modifications that keep the country on track for 2050. In my brief semester in Newcastle, I took note of these significant changes. The city of Newcastle is small enough that many students and faculty are able to walk or bike to campus and nearby essential shops. However, when driving is unavoidable, the majority of the vehicles used are electric, and many British citizens place a strong emphasis on carpooling to further reduce emissions. The United Kingdom’s determination to severely reduce greenhouse emissions is ambitious and particularly admirable, especially as the United States struggles to shy away from its dependence on fossil fuels.

So how can we, as Americans, stand together to combat global climate change? Here are five adjustments Americans can make to their homes and daily routines that can dramatically make a difference:

  • Stay cautious of food waste. Studies demonstrate that “Americans throw away up to 40 percent of the food they buy.” 21   By being more mindful of the foods we purchase, opting for leftovers, composting wastes, and donating surplus food to those in need, we can make an individual difference that impacts the greater good. 22   
  • Insulate your home. Insulation functions as a “cost-effective and accessible” method to combat climate change. 23   Homes with modern insulation reduce energy required to heat them, leading to a reduction of emissions and an overall savings; in comparison, older homes can “lose up to 35 percent of heat through their walls.” 24   
  • Switch to LED Lighting. LED stands for “light-emitting diodes,” which use “90 percent less energy than incandescent bulbs and half as much as compact fluorescents.” 25   LED lights create light without producing heat, and therefore do not waste energy. Additionally, these lights have a longer duration than other bulbs, which means they offer a continuing savings. 26  
  • Choose transportation wisely. Choose to walk or bike whenever the option presents itself. If walking or biking is not an option, use an electric or hybrid vehicle which emits less harmful gases. Furthermore, reduce the number of car trips taken, and carpool with others when applicable. 
  • Finally, make your voice heard. The future of our planet remains in our hands, so we might as well use our voices to our advantage. Social media serves as a great platform for this. Moreover, using social media to share helpful hints to combat climate change within your community or to promote an upcoming protest proves beneficial in the long run. If we collectively put our voices to good use, together we can advocate for change.

As many of us are stuck at home due to the COVID-19 pandemic, these suggestions are slightly easier to put into place. With numerous “stay-at-home” orders in effect, Americans have the opportunity to make significant achievements for climate change. Personally, I have taken more precautions towards the amount of food consumed within my household during this pandemic. I have been more aware of food waste, opting for leftovers when too much food remains. Additionally, I have realized how powerful my voice is as a young college student. Now is the opportunity for Americans to share how they feel about climate change. During this unprecedented time, our voice is needed now more than ever in order to make a difference.

However, on a much larger scale, the coronavirus outbreak has shed light on reducing global energy consumption. Reductions in travel, both on the roads and in the air, have triggered a drop in emission rates. In fact, the International Energy Agency predicts a 6 percent decrease in energy consumption around the globe for this year alone. 27   This drop is “equivalent to losing the entire energy demand of India.” 28   Complete lockdowns have lowered the global demand for electricity and slashed CO2 emissions. However, in New York City, the shutdown has only decreased carbon dioxide emissions by 10 percent. 29   This proves that a shift in personal behavior is simply not enough to “fix the carbon emission problem.” 30   Climate policies aimed to reduce fossil fuel production and promote clean technology will be crucial steppingstones to ameliorating climate change effects. Our current reduction of greenhouse gas emissions serves as “the sort of reduction we need every year until net-zero emissions are reached around 2050.” 31   From the start of the coronavirus pandemic, politicians came together for the common good of protecting humanity; this demonstrates that when necessary, global leaders are capable of putting humankind above the economy. 32

After researching statistics comparing the coronavirus to climate change, I thought back to the moment the virus reached pandemic status. I knew that a greater reason underlay all of this global turmoil. Our globe is in dire need of help, and the coronavirus reminds the world of what it means to work together. This pandemic marks a turning point in global efforts to slow down climate change. The methods we enact towards not only stopping the spread of the virus, but slowing down climate change, will ultimately depict how humanity will arise once this pandemic is suppressed. The future of our home planet lies in how we treat it right now. 

  • “Climate Change: What Do All the Terms Mean?,” BBC News (BBC, May 1, 2019), https://www.bbc.com/news/science-environment-48057733 )
  • Ibid. 
  • Kate Yoder, “Frank Luntz, the GOP's Message Master, Calls for Climate Action,” Grist (Grist, July 26, 2019), https://grist.org/article/the-gops-most-famous-messaging-strategist-calls-for-climate-action
  • Melissa Denchak, “Paris Climate Agreement: Everything You Need to Know,” NRDC, April 29, 2020, https://www.nrdc.org/stories/paris-climate-agreement-everything-you-need-know)
  • “Donald J. Trump's Foreign Policy Positions,” Council on Foreign Relations (Council on Foreign Relations), accessed May 7, 2020, https://www.cfr.org/election2020/candidate-tracker/donald-j.-trump?gclid=CjwKCAjw4871BRAjEiwAbxXi21cneTRft_doA5if60euC6QCL7sr-Jwwv76IkgWaUTuyJNx9EzZzRBoCdjsQAvD_BwE#climate and energy )
  • David Doniger, “Paris Climate Agreement Explained: Does Congress Need to Sign Off?,” NRDC, December 15, 2016, https://www.nrdc.org/experts/david-doniger/paris-climate-agreement-explained-does-congress-need-sign )
  • “How the UK Is Progressing,” Committee on Climate Change, March 9, 2020, https://www.theccc.org.uk/what-is-climate-change/reducing-carbon-emissions/how-the-uk-is-progressing/)
  • Ibid.  
  • “Top 10 Ways You Can Fight Climate Change,” Green America, accessed May 7, 2020, https://www.greenamerica.org/your-green-life/10-ways-you-can-fight-climate-change )
  • Matt McGrath, “Climate Change and Coronavirus: Five Charts about the Biggest Carbon Crash,” BBC News (BBC, May 5, 2020), https://www.bbc.com/news/amp/science-environment-52485712 )
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academic essay on climate change

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Graphic preview: the top ten most cited climate papers.

Analysis: The most ‘cited’ climate change papers

academic essay on climate change

Robert McSweeney

On Monday, we revealed the results of our survey of scientists in which we asked them to name the “most influential” climate change papers of all time.

The most popular nomination was a seminal paper by Syukuro Manabe and Richard T Wetherald published in the Journal of the Atmospheric Sciences in 1967.

Now, we turn from the subjective to the objective and look at which are the most “cited” climate change papers. Here, Carbon Brief analyses which papers have had the biggest impact in the academic world, and who wrote them.

Thousands of peer-reviewed academic papers are published about climate change every year. These articles form the bedrock of climate science, underpinning the assessment reports from the Intergovernmental Panel on Climate Change (IPCC).

With so many papers from so many journals, some inevitably sink without trace. But others become the centrepiece of their field or spark new areas of research.

Published papers

There are various databases to search through which list the thousands of academic papers published each year. Amidst options such as Google Scholar and Web of Science , we plumped for Scopus , the world’s largest abstract and citation database of peer-reviewed literature.

In Scopus, we searched for any academic paper with the phrase ‘climate change’ or ‘global warming’ in its title, abstract or keywords. We also tried using just ‘climate’ for the searches, but that produced a very broad range of articles. As we wanted to look at both the top papers and all papers far beyond the top 100, we wouldn’t have manually been able to filter out all the non-climate papers for the analysis. So we went with ‘climate change’ and ‘global warming’, though this does mean that some climate change papers without those terms in the title, abstract or keywords would miss out.

But in response to queries from some climate scientists , we’ve also, for comparison, included the top 10 ‘climate’ papers at the end of the article.

We then limited the search to give us only pure research articles, filtering out other publications such as book chapters, conference papers, review articles and editorials.

The search yields a total of almost 120,000 papers, as of the beginning of June this year. You can see below how the number of published papers about climate change took off during the 2000s.

Total number of climate change papers published, by year. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Total number of climate change papers published, by year. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

As the chart below shows, most of the papers relate to environmental science (25% of papers), earth and planetary science (22%) and agricultural and biological sciences (16%). But the search also unearths papers from social science (8%), medicine (3%) and even dentistry (0%, or 4 papers).

Subject of climate change papers, by topic area. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Subject of climate change papers, by topic area. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Most prolific

Across all 120,000 papers, the most prolific author is Dr Philippe Ciais from the Laboratoire des Sciences du Climat and de l’Environment in Paris. Ciais has 120 published articles on climate change, mostly about the global carbon cycle.

Coming in second is Prof Richard Tol , from the Department of Economics at the University of Sussex , with 113. And third place goes to Prof Josep Penuelas , director of the Global Ecology Unit at the Universitat Autònoma de Barcelona . You can see the rest of the top 10 in the graphic below.

Top 10 most prolific authors of climate change papers. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Top 10 most prolific authors of climate change papers. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

But while the number of publications shows how prolific a researcher is, it doesn’t reveal how influential their work is. To do that we need to look at citations.

Citation, citation, citation

In an academic paper, scientists will refer to previous work by other scientists in their field.  This may be to set the scene of their research or acknowledge a method or finding that someone else produced. In doing this they refer to, or ‘cite’, other academic papers.

Databases such as Scopus keep track of how many times each paper has been cited by others. We extracted the 100 most cited climate change papers.

The top paper, with 3,305 citations, is Nature paper, ” A globally coherent fingerprint of climate change impacts across natural systems “, by Prof Camille Parmesan , at the University of Texas and Plymouth University , and Prof Gary Yohe , from Wesleyan University .

Published in 2003, the paper assessed the global impact of climate change on more than 1,700 biological species, from birds and butterflies to trees and alpine herbs. Parmesan and Yohe found that 279 species are already being affected by climate change, and 74-91% of these changes agree with what is expected from projections.

This paper also featured in our analysis as one of the papers that IPCC authors considered the most influential .

In runners-up spot is an Ecological Modelling paper from 2000, ” Predictive habitat distribution models in ecology “, with 2,746 citations. The paper was written by Prof Antoine Guisan , now of the Université de Lausanne , and Dr Niklaus Zimmerman of the Swiss Federal Research Institute .

And coming in third is ” Extinction risk from climate change “, again published in Nature, with 2,562 citations. This 2004 paper has 19 authors, but the lead was Dr Chris Thomas from the University of Leeds .

Our infographic below shows the top 10 most cited papers on climate change.

Top 10 most cited climate change papers. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Top 10 most cited climate change papers. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Apart from the Parmesan and Yohe article, just one of our top most influential papers according to IPCC authors makes the top 100 of most cited. This is the Journal of Climate paper “ Robust responses of the hydrological cycle to global warming “, by Prof Isaac Held and Prof Brian Soden , which comes in 34th.

So where are the climatic luminaries of Syukuro Manabe , Guy Callendar and Charles Keeling ? Well, primarily, Scopus doesn’t yet have complete citations for papers published before 1996, so older papers might be underrepresented in the top 100 most cited.

But another reason could be that papers tend to have more citations in recent years because there are more papers on climate change being published, so more opportunities to be cited. This is reflected in the top 100, where most are from 2000 onwards, and none before 1988.

Likewise, very recent papers don’t appear in the top 100 because they haven’t been around long enough to accrue citations. The most recent paper in the top 100 was published in 2011.

Most appearances

So we’ve looked at which authors produce the most papers, but which have appeared most often in the top 100 of cited papers? No researcher appeared more than twice as a lead author, but four appeared as at least a co-author in five papers.

Featuring in this group is, once again, Prof Ciais. But alongside him with five papers are Dr Josep Canadell , the executive director of the Global Carbon Project at the Commonwealth Scientific and Industrial Research Organisation ( CSIRO ) in Australia, Dr Richard Houghton , a senior scientist at Woods Hole Research Center in Massachusetts, and Prof Colin Prentice , professor of life sciences at Imperial College London .

Beyond the leading four, another two researchers are authors on four papers, and a further ten have authored three. This makes up a top 16 of authors behind the 100 most cited papers, which you can see in the graphic below.

Top 16 authors with the most papers in the top 100 most cited. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Top 16 authors with the most papers in the top 100 most cited. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Western focus

We also looked at which institutions were behind the top 100 papers. This time we just concentrated on the primary institution that each paper’s lead author was affiliated to.

Two come out top, with six papers each: the University of East Anglia , and the National Center for Atmospheric Research in the US. In total, there are 17 institutions with at least two papers in the top 100.

Looking at the countries where these institutions reside, there is a prominent leaning towards western countries in the northern hemisphere. The US and the UK dominate, with almost three-quarters of the top 100 papers.

Papers in the top 100, by institution. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Papers in the top 100, by institution. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

The rest are sprinkled through Europe, with a few further afield, including Australia, China and Costa Rica.

For comparison, we’ve also mapped which countries all 120,000 papers were authored from. Although note this isn’t a direct comparison, because this data include the locations of all the authors on each paper, not just the lead.

Scopus -map -2

Map of countries with most papers, for the top 100 most cited (top), and for all climate change papers (bottom). Data from Scopus. Credit: Rosamund Pearce, Carbon Brief and © OpenStreetMap contributors © CartoDB.

You can see again that researchers in the US and UK are responsible for the bulk of climate change papers, but, interestingly, China comes in third with 7%. Looking into the data, over a fifth of these papers have an author from the Chinese Academy of Sciences.

In fact, according to Scopus, over 2,200 of all 120,000 papers have at least one author from the Chinese Academy, though just one makes into our top 100 most cited.

Top journals

Finally, we looked at where our top 100 most-cited papers were published. And there were no surprises here. Top of the tree are journal powerhouses  Nature  (27 papers) and  Science  (26), accounting for over half of the top 100, and Nature has six of the top 10. This doesn’t include sister journals, such as  Nature Climate Change  or  Science Advances .

Trailing behind at some distance are  Journal of Climate  (9),  Proceedings of the National Academy of Sciences  (4) and  Review of Geophysics  (3). No other journal makes more than two appearances in the top 100.

Pie chart showing top 100 climate papers, by journal. Data from Scopus.

Top 100 climate papers, by journal. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

But do Nature and Science only come out top because they publish the most articles on climate change? According to Scopus, it seems not.

Of all 120,000 papers, most were published by Geophysical Research Letters (3,057 papers), followed by Journal of Climate (2,600) and Climatic Change (2,200). Nature comes in 12th (839) and Science way down in 20th (625).

Here’s the entire Top 100 list if you want to have a look yourself.

Top ‘climate’ papers

As we mentioned earlier, searching for papers on “climate change” or “global warming” may mean overlooking some climate-related papers that don’t necessarily have these terms in their title, abstract or keywords. So, for comparison, below is the top 10 most cited “climate” papers.

Top 10 most cited climate papers. Differences in citation numbers between top 10 climate papers and top 10 climate change papers (see earlier graphic) are because the database was searched on different days. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

Top 10 most cited climate papers. Differences in citation numbers between top 10 climate papers and top 10 climate change papers (see earlier graphic) are because the database was searched on different days. Data from Scopus. Credit: Rosamund Pearce, Carbon Brief

The most cited “climate” paper is ” The NCEP/NCAR 40-year reanalysis project “, with a total of 13,905 citations. The paper has 22 authors, but the lead was Prof Eugenia Kalnay , then at the National Centers for Environmental Prediction at NOAA in the US, but now of the University of Maryland .

Published in the journal Bulletin of the American Meteorological Society in 1996, the paper describes the development of a 40-year global climate record, which has been used – and hence cited – in thousands of other climate studies.

Graphic preview: The top ten most cited climate papers.

Updated on 10 July 2015: We amended the top15 most cited authors infographic to add in a scientist we missed out.

  • Analysis: The most 'cited' climate change papers

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Home / For Educators: Grades 6-12 / Climate Explained: Introductory Essays About Climate Change Topics

Climate Explained: Introductory Essays About Climate Change Topics

Filed under: backgrounders for educators ,.

Climate Explained, a part of Yale Climate Connections, is an essay collection that addresses an array of climate change questions and topics, including why it’s cold outside if global warming is real, how we know that humans are responsible for global warming, and the relationship between climate change and national security.

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academic essay on climate change

Climate Change Basics: Five Facts, Ten Words

Backgrounders for Educators

To simplify the scientific complexity of climate change, we focus on communicating five key facts about climate change that everyone should know. 

academic essay on climate change

Why should we care about climate change?

Having different perspectives about global warming is natural, but the most important thing that anyone should know about climate change is why it matters.  

academic essay on climate change

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Looking for resources to help you and your students build a solid climate change science foundation? We’ve compiled a list of reputable, student-friendly links to help you do just that!  

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academic essay on climate change

The Center for Global Studies

Climate change argumentation.

Carmen Vanderhoof, Curriculum and Instruction, College of Education, Penn State

Carmen Vanderhoof is a doctoral candidate in Science Education at Penn State. Her research employs multimodal discourse analysis of elementary students engaged in a collaborative engineering design challenge in order to examine students’ decision-making practices. Prior to resuming graduate studies, she was a secondary science teacher and conducted molecular biology research. 

  • Subject(s):  Earth Science
  • Topic:  Climate Change and Sustainability
  • Grade/Level:  9-12 (can be adapted to grades 6-8)
  • Objectives:  Students will be able to write a scientific argument using evidence and reasoning to support claims. Students will also be able to reflect on the weaknesses in their own arguments in order to improve their argument and then respond to other arguments.
  • Suggested Time Allotment:  4-5 hours (extra time for extension)

This lesson is derived from Dr. Peter Buckland’s sustainability  presentation for the Center for Global Studies . Dr. Peter Buckland, a Penn State alumnus, is a postdoctoral fellow for the Sustainability Institute. He has drawn together many resources for teaching about climate change, sustainability, and other environmental issues. 

While there are many resources for teaching about climate change and sustainability, it may be tough to figure out where to start. There are massive amounts of data available to the general public and students need help searching for good sources of evidence. Prior to launching into a search, it would be worthwhile figuring out what the students already know about climate change, where they learned it, and how they feel about efforts to reduce our carbon footprint. There are many options for eliciting prior knowledge, including taking online quizzes, whole-class discussion, or drawing concept maps. For this initial step, it is important that students feel comfortable to share, without engaging in disagreements. The main idea is to increase students’ understanding about global warming, rather than focus on the potential controversial nature of this topic.

A major goal of this unit is to engage students in co-constructing evidence-based explanations through individual writing, sharing, re-writing, group discussion, and whole group reflection. The argumentation format presented here contains claims supported by evidence and reasoning (Claims Evidence Reasoning – CER). Argumentation in this sense is different from how the word “argument” is used in everyday language. Argumentation is a collaborative process towards an end goal, rather than a competition to win (Duschl & Osborne, 2002). Scientific argumentation is the process of negotiating and communicating findings through a series of claims supported by evidence from various sources along with a rationale or reasoning linking the claim with the evidence. For students, making the link between claim and evidence can be the most difficult part of the process.

Where does the evidence come from?

Evidence and data are often used synonymously, but there is a difference. Evidence is “the representation of data in a form that undergirds an argument that works to answer the original question” (Hand et al., 2009, p. 129). This explains why even though scientists may use the same data to draw explanations from, the final product may take different forms depending on which parts of the data were used and how. For example, in a court case experts from opposing sides may use the same data to persuade the jury to reach different conclusions. Another way to explain this distinction to students is “the story built from the data that leads to a claim is the evidence” (Hand et al., 2009, p. 129). Evidence can come from many sources – results from controlled experiments, measurements, books, articles, websites, personal observations, etc. It is important to discuss with students the issue of the source’s reliability and accuracy. When using data freely available online, ask yourself: Who conducted the study? Who funded the research? Where was it published or presented? 

What is a claim and how do I find it?

A scientific claim is a statement that answers a question or an inference based on information, rather than just personal opinion.               

How can I connect the claim(s) with the evidence?

That’s where the justification or reasoning comes in. This portion of the argument explains why the evidence is relevant to the claim or how the evidence supports the claim.


Learning context and connecting to state standards.

This interdisciplinary unit can be used in an earth science class or adapted to environmental science, chemistry, or physics. The key to adapting the lesson is guiding students to sources of data that fit the discipline they are studying.

For  earth science , students can explain the difference between climate and weather, describe the factors associated with global climate change, and explore a variety of data sources to draw their evidence from.  Pennsylvania Academic Standards  for earth and space science (secondary): 3.3.12.A1, 3.3.12.A6, 3.3.10.A7.    

For  environmental science , students can analyze the costs and benefits of pollution control measures.  Pennsylvania Academic Standards  for Environment and Ecology (secondary): 4.5.12.C.          

For  chemistry  and  physics , students can explain the function of greenhouse gases, construct a model of the greenhouse effect, and model energy flow through the atmosphere.   Pennsylvania Academic Standards  for Physical Sciences (secondary): 3.2.10.B6.      

New Generation Science Standards (NGSS) Connections

Human impacts and global climate change are directly addressed in the NGSS.  Disciplinary Core Ideas  (DCI): HS-ESS3-3, HS-ESS3-4, HS-ESS3-5, HS-ESS3-6.     

Lesson 1: Introduction to climate change

  • What are greenhouse gases and the greenhouse effect? (sample answer: greenhouse gases like carbon dioxide and methane contribute to overall heating of the atmosphere; these gases trap heat just like the glass in a greenhouse or in a car) 
  • What is the difference between weather and climate? (sample answer: weather is the daily temperature and precipitation measurements, while climate is a much longer pattern over multiple years)

Drawing of the greenhouse effect  – as individuals or in pairs, have students look up the greenhouse effect and draw a diagram to represent it; share out with the class

  • Optional: figure out students’ beliefs about global warming using the Yale Six Americas Survey (students answer a series of questions and at the end they are given one of the following categories: alarmed, concerned, cautious, disengaged, doubtful, dismissive).

Lesson 2: Searching for and evaluating evidence

  • Compare different data sources and assess their credibility
  • Temperature
  • Precipitation
  • Storm surge
  • Ask the students to think about what types of claims they can make about climate change using the data they found (Sample claims: human activity is causing global warming or sea-level rise in the next fifty years will affect coastal cities like Amsterdam, Hong Kong, or New Orleans).

Lesson 3: Writing an argument using evidence

  • Claim – an inference or a statement that answers a question
  • Evidence – an outside source of information that supports the claim, often drawn from selected data
  • Reasoning –  the justification/support for the claim; what connects the evidence with the claim
  • Extending arguments –  have students exchange papers and notice the strengths of the other arguments they are reading (can do multiple cycles of reading); ask students to go back to their original argument and expand it with more evidence and/or more justification for why the evidence supports the claim
  • Anticipate Rebuttals  – ask students to think and write about any weaknesses in their own argument

Lesson 4: Argumentation discussion  

  • rebuttal  – challenges a component of someone’s argument – for example, a challenge to the evidence used in the original argument
  • counterargument  – a whole new argument that challenges the original argument
  • respect group members and their ideas
  • wait for group members to finish their turns before speaking
  • be mindful of your own contributions to the discussion (try not to take over the whole discussion so others can contribute too; conversely, if you didn’t already talk, find a way to bring in a new argument, expand on an existing argument, or challenge another argument)  
  • Debate/discussion  – In table groups have students share their arguments and practice rebuttals and counterarguments
  • Whole-group reflection  – ask students to share key points from their discussion

Lesson 5: Argumentation in action case study

Mumbai, india case study.

Rishi is a thirteen year old boy who attends the Gayak Rafi Nagar Urdu Municipal school in Mumbai. There is a massive landfill called Deonar right across from his school. Every day 4,000 tons of waste are piled on top of the existing garbage spanning 132 hectares (roughly half a square mile). Rishi ventures out to the landfill after school to look for materials that he can later trade for a little bit of extra money to help his family. He feels lucky that he gets to go to school during the day; others are not so lucky. One of his friends, Aamir, had to stop going to school and work full time after his dad got injured. They often meet to chat while they dig through the garbage with sticks. Occasionally, they find books in okay shape, which aren’t worth anything in trade, but to them they are valuable.

One day Rishi was out to the market with his mom and saw the sky darken with a heavy smoke that blocked out the sun. They both hurried home and found out there was a state of emergency and the schools closed for two days. It took many days to put out the fire at Deonar. He heard his dad say that the fire was so bad that it could be seen from space. He wonders what it would be like to see Mumbai from up there. Some days he wishes the government would close down Deonar and clean it up. Other days he wonders what would happen to all the people that depend on it to live if the city shuts down Deonar.

Mumbai is one of the coastal cities that are considered vulnerable with increasing global temperature and sea level rise. The urban poor are most affected by climate change. Their shelter could be wiped out by a tropical storm and rebuilding would be very difficult.

Write a letter to a public official who may be able to influence policy in Mumbai.

What would you recommend they do? Should they close Deonar? What can they do to reduce air pollution in the city and prepare for possible storms? Remember to use evidence in your argument.  

If students want to read the articles that inspired the case study direct them to: http://unhabitat.org/urban-themes/climate-change/





  • Lines of Evidence  video  from the National Academies of Sciences, Engineering, and Medicine  http://nas-sites.org/americasclimatechoices/videos-multimedia/climate-change-lines-of-evidence-videos/  
  • Climate Literacy and Energy Awareness Network  (CLEAN) 
  • Climate maps  from the National Oceanic and Atmospheric Administration
  • Sources of data from  NASA
  • Explore the original source of the  Proceedings of the National Academies of Sciences (PNAS) study

Differentiated Instruction

  • For visual learners – use diagrams, encourage students to map out their arguments prior to writing them
  • For auditory learners – use the lines of evidence video
  • For ESL students – provide them with a variety of greenhouse gases diagrams, allow for a more flexible argument format and focus on general meaning-making – ex. using arrows to connect their sources of evidence to claims
  • For advanced learners – ask them to search through larger data sets and make comparisons between data from different sources; they can also research environmental policies and why they stalled out in congress 
  • For learners that need more support – print out excerpts from articles; pinpoint the main ideas to help with the research; help students connect their evidence with their claims; consider allowing students to work in pairs to accomplish the writing task 

Argument write-up  – check that students’ arguments contain claims supported by evidence and reasoning and that they thought about possible weaknesses in their own arguments. 

Case study letter  – check that students included evidence in their letter.


Duschl, R. A., & Osborne, J. (2002). Supporting and promoting argumentation discourse in science education.

Hand, B. et al. (2009) Negotiating Science: The Critical Role of Argumentation in Student Inquiry. Portsmouth, NH: Heinemann.

McNeill, K. L., & Krajcik, J. (2012). Claim, evidence and reasoning: Supporting grade 5 – 8 students in constructing scientific explanations. New York, NY: Pearson Allyn & Bacon.

Sawyer, R. K. (Ed.). (2014). The Cambridge handbook of the learning sciences. New York, NY: Cambridge University Press.



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Research Article

The role of climate change education on individual lifetime carbon emissions

Roles Conceptualization, Funding acquisition, Investigation, Methodology, Project administration, Supervision, Writing – original draft

* E-mail: [email protected]

Affiliation Department of Meteorology and Climate Science, San José State University, San José, California, United States of America

ORCID logo

Roles Formal analysis, Writing – review & editing

Roles Conceptualization, Methodology, Writing – review & editing

Affiliation Department of Communication Studies, San José State University, San José, California, United States of America

  • Eugene C. Cordero, 
  • Diana Centeno, 
  • Anne Marie Todd


  • Published: February 4, 2020
  • https://doi.org/10.1371/journal.pone.0206266
  • Reader Comments

Table 1

Strategies to mitigate climate change often center on clean technologies, such as electric vehicles and solar panels, while the mitigation potential of a quality educational experience is rarely discussed. In this paper, we investigate the long-term impact that an intensive one-year university course had on individual carbon emissions by surveying students at least five years after having taken the course. A majority of course graduates reported pro-environmental decisions (i.e., type of car to buy, food choices) that they attributed at least in part to experiences gained in the course. Furthermore, our carbon footprint analysis suggests that for the average course graduate, these decisions reduced their individual carbon emissions by 2.86 tons of CO 2 per year. Surveys and focus group interviews identify that course graduates have developed a strong personal connection to climate change solutions, and this is realized in their daily behaviors and through their professional careers. The paper discusses in more detail the specific components of the course that are believed to be most impactful, and the uncertainties associated with this type of research design. Our analysis also demonstrates that if similar education programs were applied at scale, the potential reductions in carbon emissions would be of similar magnitude to other large-scale mitigation strategies, such as rooftop solar or electric vehicles.

Citation: Cordero EC, Centeno D, Todd AM (2020) The role of climate change education on individual lifetime carbon emissions. PLoS ONE 15(2): e0206266. https://doi.org/10.1371/journal.pone.0206266

Editor: Francesco S. R. Pausata, Universite du Quebec a Montreal, CANADA

Received: October 5, 2018; Accepted: January 7, 2020; Published: February 4, 2020

Copyright: © 2020 Cordero et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: Data are available at OSFHOME, and access to the data can be found at ( https://osf.io/an4ht/ ), with this reference: DOI 10.17605/OSF.IO/AN4HT .

Funding: The National Science Foundation under grant 1513332 provided support for the partial salary of DC, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section. The commercial company Green Ninja did not provide any financial support related to this research, nor did they have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: I have read the journal’s policy and the authors of this manuscript have the following competing interests: EC is the majority owner of Green Ninja, an education company that produces middle school curriculum. A conflict of interest plan has been established through San Jose State University. This does not alter our adherence to PLOS ONE policies on sharing data and materials as detailed online in our guide for authors http://journals.plos.org/plosone/s/competing-interests .

1. Introduction

In 1992, the United Nations Framework Convention on Climate Change (UNFCC) stated, “Education is an essential element for mounting an adequate global response to climate change” [ 1 ]. Few would argue against the importance of education in providing an informed response to environmental problems. Solutions to climate change tend to focus on mitigation and adaptation measures, and successful implementation of either strategy requires an informed and educated citizenry. Interest in education and climate change has increased in recent years [ 2 ] in part due to leadership efforts from organizations like the United Nations Education, Scientific, and Cultural Organization (UNESCO) that continue to advocate for educational efforts to respond to climate change [ 3 ]. Yet despite the notion of education’s importance in responding to climate change, education is rarely mentioned in discussions of today’s major climate solution strategies. One reason that education programs may not feature prominently in discussions about climate change mitigation is that few studies verify the effective reductions in carbon emissions resulting from education programs. Although several studies have linked environmental education and environmental quality (e.g., Education and water quality [ 4 ]; Education and air quality [ 5 ]; and Education and energy reduction [ 6 ]), the environmental education literature is relatively sparse [ 7 ]. And while the potential to reduce carbon emissions through behavior programs is clear (e.g., [ 8 ]), connections to education over time have not been as well established [ 9 ]. This is in contrast to technologies such as renewable energy generation and the electrification of automobiles that can demonstrate reductions in carbon emissions using more easily accessible data. Should education be shown to be an effective tool to reducing emissions via changes in attitudes and behavior, it would seem likely that funding and interest in such methods would become more widespread and well supported.

Education has been found to be one method for promoting behavior change, but only under certain circumstances (e.g., [ 10 ]; [ 11 ]). The environmental education literature offers insights into the connections between education and behavior change, and it also provides guidance on how to encourage pro-environmental behavior [ 12 ]; [ 13 ]; [ 14 ]; [ 15 ]. The notion that knowledge leads to awareness and then to action has been countered with studies that document that knowledge and skills are not enough to change behavior (e.g., [ 16 ]). The literature suggests that more personal factors such as a deep connection to nature, personal relevance to the issue and personal agency towards action are important elements that contribute to successful behavior change programs (e.g., [ 10 ]; [ 17 ]; [ 18 ]; [ 19 ]). Even among successful programs, the question of how long the intended behavior is sustained can vary depending on the type of intervention, with longer and more sustained engagements tending to have more long-lasting impacts [ 20 ]. This previous research informs educational research programs towards designs that not only focus on information but also promote the personal qualities that can support sustained action.

A growing base of literature is developing around climate change education as national standards move towards inclusion of this subject in the core curriculum [ 21 ], and educators negotiate the teaching of this sometimes ‘controversial’ subject (e.g., [ 22 ]; [ 23 ]; [ 24 ]). While there are similarities to the teaching of other environmental topics, climate change includes some unique education challenges that make teaching this topic especially difficult [ 25 ]; [ 26 ]; [ 27 ]. The science is highly complex and spans various areas in the natural and physical sciences, and yet the implications of our changing climate and the role of human activities make this scientific topic both a social and a political issue. Despite the goals of environmental education organizations like the UNESCO, relatively few climate change education programs remain that have successfully demonstrated the type of behavior change needed to effectively respond to climate change [ 23 ]; [ 28 ]; [ 29 ]. Further, even among existing climate change education resources offered in textbooks and through government programs, it appears there are opportunities to promote more effective emission-reduction strategies [ 30 ].

The purpose of this paper is to evaluate the impact of an intensive university climate change course on individual long-term carbon emissions. The design of the course is described including the background research framework that was employed to help students develop a deep connection with climate change and climate solutions. Five years of graduates from the course were surveyed at least five years after they took the course. The results of both survey data and focus group interviews provide an indication of the long-term impact of the course, and they contribute to our understanding of the potential role that education can play in long-term behaviors and attitudes. We then quantify the reductions in annual carbon emissions resulting from graduates’ pro-environmental behavior, and we compare the reductions achieved through this education program with other climate change mitigation measures. Additional discussion is provided about the educational approach and the factors we felt were critical to the success of the education program.

The San Jose State University IRB committee has approved this human subject research (F15035) and all participants have provided written consent.

2.1. University course and students

In fall 2007, a new course was offered at San José State University (SJSU) that satisfied all three subject areas of the upper division general education (GE) requirements, plus the campus upper division writing requirement. The course, COMM/ENVS/GEOL/HUM/METR 168 & 168W: Global Climate Change I & II (hereafter referred to as COMM 168), is taught over an academic year, with six credit hours in the fall semester, and three credit hours in the following spring semester. The course is team taught by three faculty members from different departments with expertise in the core themes of climate science, climate mitigation and environmental communication. Although different professors taught the course during the five-year study period, the syllabus was consistent through the five years. During this same five-year period, student enrollment came from a broad distribution of the campus colleges, as shown in Table 1 . The course uses a number of design approaches to impact students in ways that maximize effects on students’ personal and professional lives, and this is described in more detail in section 3, Course Design. COMM 168 has been taught every year since 2007 and continues to be a well-enrolled class at SJSU.


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2.2. Survey and focus groups

An 18-item survey instrument (provided in the S1 Text ) was developed to study participants’ beliefs about climate change and whether their own personal actions to mitigate climate change could be associated with taking the COMM 168 course. The survey was broadly based on questions about climate change drawn from [ 31 ] and [ 32 ], and included questions that used a five-element Likert scale (strongly agree, agree, don’t know, disagree, or strongly disagree), multiple choice, and free response. A draft survey was trialed at SJSU by other educators and was revised based on their feedback. Of the more than 500 students who took the course, 104 students from the five different course iterations between 2007 and 2012 completed the survey. We emphasize that the survey was given to students at least five years after they completed the course, and no surveys were given before participants took the course. The categories of questions focused on participants’ a) attitudes and beliefs about global warming and whether they perceive it to affect them personally, and b) whether any of the participants’ current pro-environmental behaviors can be attributed to taking the COMM 168 course. The survey data was collected using an online platform where participant email was used to ensure only one response was collected per participant. Once the data was collected, spreadsheet statistical techniques, including pivot tables, were used to analyze participant data based on responses to different items.

After evaluating the survey responses and noting themes in the utility of the course and personal climate change mitigation strategies, we followed up with focus group interviews to gain more in-depth understanding of the enduring influence of the course on students’ personal and professional lives. Including a qualitative approach, such as focus group interviews, can complement the survey analysis and ultimately enhance the quality of the resulting analysis [ 33 ].

Focus group participants were randomly selected from the 100+ survey respondents. We conducted two focus groups with a total of five participants in a classroom at San José State University. Participants were asked a series of open-ended questions about the course and its impact on their current lives. Once the focus group interviews were completed, focus group transcripts were analyzed according to thematic analysis. The goal of a thematic analysis was to identify patterns in the data to bring clarity to the research questions. First, we interpreted patterns in the focus group responses by identifying themes in the transcripts that were common across the interviewees in different focus groups. Then select quotes and phrases were chosen to illustrate the identified themes. These quotes and phrases were woven into a narrative to describe the focus group responses in a coherent way. This exploratory approach to thematic analysis enabled us to present a rich description of student experiences in the course and perceptions of climate change issues. Copies of the survey, focus group scripts, and focus group protocols are provided in S1 and S3 Texts.

2.3. Estimating carbon emission reductions from the survey responses

Once responses to the survey questions were obtained, the potential carbon reductions from the decisions made by participants were estimated. Details of the procedure used are provided in S2 Text , but we briefly describe the method here. We use the CoolClimate Calculator [ 34 ] an online household carbon footprint calculator that has been well documented and verified in a number of studies (e.g., [ 35 ]; [ 36 ]; [ 37 ]; [ 38 ]). The carbon footprint calculator is used to estimate how a particular action attributed to taking COMM 168 would impact individual annual carbon emissions. We start by calculating the annual carbon emissions for an average person in California. Then, based on the response to a particular question (e.g., participant attributed their current purchasing of renewable energy from their utility to the COMM 168 course), we use the calculator to determine the reduction in annual carbon emissions due to that particular action (e.g., participant reduced emissions by 1.38 tons/year by purchasing renewable energy from their utility). This procedure is repeated for each of the actions identified in the survey, and thus allows us to estimate how particular actions have changed individual carbon emissions. We acknowledge that although participants attributed particular actions to the COMM 168 course, other experiences either before or after the course may have also contributed towards these pro-environmental attitudes and behaviors. Our notion is that this intensive one-year class on climate change played a key or leading role in the development of these attitude and behaviors.

3. Course design

The COMM 168 course was designed to promote lasting responsible environmental behavior through an educational model broadly based on the environmental education research of [ 17 ]. In this research, Hungerford and Volk identified three predictor variables or factors that contribute to pro-environmental behavior. The first factor is labeled as an entry-level variable and describes the importance of an empathetic perspective towards nature and the environment. The second factor is labeled as the ownership variables and describes the importance of both in-depth knowledge about the issue and a personal connection to the issue. The third factor is the empowerment variable, and this describes the understanding and skills around solutions to the issue, together with a sense of personal agency. As described in various later studies (e.g., [ 10 ]; [ 39 ]; [ 40 ], these three factors are important components to successful behavior change educational programs.

To illustrate the theoretical connection between the design elements of the course and the expected outcomes, we use a conjecture map in Fig 1 [ 41 ] to illustrate what we believe are the most salient connections between the primary conjecture, key elements of the intervention design, the measurable mediating processes and the intervention outcomes. This framework outlines the intermediate processes that support learning, and offers opportunities to measure the effectiveness of these mediating processes towards the intervention outcomes.


In the course design column, the item superscripts indicate an alignment with predictor variables (i.e., 1—entry level; 2—ownership; 3—empowerment).


The course design includes two primary tools that aim to provide students with the key learning experiences that will lead to the intended outcomes. The first tool is a series of activities where students explore connections between their personal and professional lives and climate change. The second tool is the community action project, where student teams design and implement plans to reduce carbon emissions in a community of their choice. Each of these tools, together with other learning experiences in the class, are structured around the three key focus areas of climate science, climate solutions and communication. Examples of the primary tools followed by the mediating processes are provided below.

The COMM 168 course used a series of activities to help students develop a stronger connection to climate change and to leverage the predictor factors that have been found to promote behavior change. We provide three examples of learning activities that leveraged each of these predictor factors. In one activity focused on careers, students write a paper, supported by research, about the importance of climate change in their specific discipline. The audience of the paper are peers in their field, and students identify at least three reasons why climate change would be important in their discipline. This career activity is most closely aligned with the ownership variable. In another activity focused on individual action, students use an online calculator to compute their own carbon footprint based on their lifestyle, and then they develop a plan for how to reduce their carbon footprint by 10%. Students then implement their carbon reduction plan for a week and report on their experiences. This activity is most closely aligned with the empowerment variable. In a third activity, students participate in a multi-day United Nations (UN) climate negotiation simulation, where students play the role of a delegate representing a specific nation or bloc of nations. This activity provided students with unique perspectives on the impacts of climate change on vulnerable communities, and this activity was most strongly associated with the entry-level variable.

The other primary tool used in the course design is the community action project (CAP), a year-long culminating experience that threads through the two semesters. In the CAP, student teams build on their course knowledge to develop, design and implement projects that respond to climate change in local communities. During the first semester, student teams are formed and develop proposals for their community action project, while in the second semester, student teams are focused on developing and implementing their projects. Examples of CAPs include developing community gardens in the local neighborhood, presenting climate lessons in schools, and creating campaigns to help individuals and businesses move towards some type of climate action. At the end of the second semester, a panel of external judges comprising local government and industry award prizes to the teams with the most innovative and successful projects. The CAP allows students the opportunities to apply their learning in a way that is meaningful and impactful, and there is strong alignment between CAP projects and the predictor variables described above.

Supporting these two instructional tools are the three key focus areas of climate science, climate solutions and environmental communication. For the focus area of climate science, the instruction provides an understanding of the natural and anthropogenic factors that affect the Earth’s climate. Students study the past climate to understand natural factors, and then they focus on the current climate where human activities are the dominant contributor to contemporary changes. Tools like radiative forcing and climate models are used to help students identify evidence connecting human activities and climate change.

For the focus area of climate solutions, students study how both policy mechanisms and personal actions can help mitigate climate change. Through various case studies, students look at the role that local, state and national policies can have on improving environmental conditions. Related issues such as environmental justice and the slow uptake of climate action in government are also discussed. Other areas of climate change mitigation include studies of personal behavior around subjects like food, transportation and home energy use.

For the focus area of environmental communication, students look at marketing and communication strategies and the ideas around framing for particular audiences. Students study various media campaigns and develop experience creating their own communication tools designed for a particular audience. A component of this also focuses on analyzing the current public discourse around climate change and how various stakeholders play a role in shaping these discussions.

As referenced in the conjecture map of Fig 1 , these course design elements support a number of mediating processes that ultimately can lead to actions and behaviors that reduce carbon emissions. Aspects of the mediating processes and intervention outcomes can be measured using various tools. In this study we have used surveys and focus group interviews to explore students’ knowledge and attitudes about climate change at least five years after completing the course.

The design elements of the course were developed to achieve the stated outcome of developing a personal connection to climate change and participating in behaviors that reduce carbon emissions. As is the case in many educational settings, along the way faculty made adjustments to the course and their teaching to help promote student engagement. However, the primary course design tools and key focus areas were constant throughout the five study years. A copy of the original syllabus is provided in S4 Text .

Finally, when developing this course more than 10 years ago, we were focused on creating a contemporary and action-based learning experience. Only later did we realize that this learning environment was creating unique outcomes, worthy of further study. Although it would have been preferable to have also collected data before and during the course experience, the type of longitudinal analyses presented here is rare in environmental education, and our methodology, although subject to some limitations, provides a unique opportunity to investigate the long-term role of education on personal behavior.

As described in Sections 2.2 and 2.3, we use surveys and focus groups to study the attitudes and behaviors of graduates of COMM 168 after more than five years following the course completion. These results are analyzed in the below sections.

4.1. Survey

The first part of the survey focused on participants’ attitudes and beliefs about global warming. A large majority of participants (83%) agreed with the statement, “Most scientists think global warming is happening.”, and most participants (84%) also felt that global warming would affect their lives “a great deal” or “a moderate amount.” This is notable since the general public often discounts the impacts that global warming will have on them personally [ 42 ]; [ 43 ]. Most participants (84%) also strongly agreed or agreed with the statement, “I have personally experienced the effects of global warming.”, and when asked about how global warming will affect future generations, 91% said “a great deal.” Because these results are quite different from the average U.S. general public (e.g., [ 44 ]), this suggests that the course may have had an influence on students’ long-term beliefs about climate change. Even so, we cannot rule out the possibility that a socially-agreeable bias may be present in participant responses, as described further in the Section 7.

The second group of questions asked about personal actions to reduce climate change and whether the COMM 168 course had any effect on those actions. The general areas of climate action included waste reduction, home energy conservation, transportation and food choices. Each question asked participants to reflect on how participation in COMM 168 may have affected their actions today in those areas.

A summary of the results for the different categories is provided in Fig 2 . In the waste and home energy conservation categories, a large percentage of participants described engaging in some actions to reduce waste or reduce energy use in their home that they attribute to taking the COMM 168 course. This included recycling more often (95%), changing to more energy efficient light bulbs (86%), giving away or donating products so they can be reused (75%), buying products that have less packaging (64%), and purchasing energy-efficient appliances (59%). Fewer participants reported actions such as composting food scraps (48%), purchasing renewable energy from their utility (18%) and installing solar panels (4%).


The blue bars represent the percentage of students who agreed with the survey response, while the orange bars represent the impact in carbon emissions in percent relative to the total reductions.


In the transportation category, about 25% of participants reported some behavior to reduce emissions that is attributed to the COMM 168 course. This included using public transportation more (35%), using a bicycle for transportation (26%) and carpooling regularly (22%). And in the food choices category, most participants (80%) reported that at least occasionally they made food choices based on reducing carbon emissions.

The survey responses reported here suggest that participant behavior was influenced by the COMM 168 course in ways that continue to impact daily life. The types of actions studied here can be divided into two groups: one-time actions and recurring actions. For example, the purchase of an energy-efficient light bulb or automobile is a one-time action, and these decisions will shape energy use for years into the future. In contrast, recurring actions such as recycling or food choices are made every day, and thus require more consistent engagement or behavior response. In reality, pro-environmental behavior includes both types of actions, and their impacts on carbon emissions can vary depending on the type of action and whether recurring actions become part of an individual’s lifestyle. Given the number of years that elapsed between the course and the survey, the survey provides a glimpse into behaviors that have likely become habitual. In the waste and food categories, some recurring actions were noted by most participants. Although recycling may be viewed as a fairly common action in many Californian communities, food choices and the connection with carbon emissions is not as widely known by the general public (e.g., [ 30 ]; [ 31 ]). Given that 80% of participants reported some changes to their food choices, it appears that the course did have an impact on decision-making in this category even years after the course.

4.1.1. Estimated carbon emissions.

Using the survey responses about the actions that participants took, we estimate the reductions in carbon emissions for all participants using a household carbon footprint calculator. Fig 2 also shows the contribution of each of the survey questions to the total reductions in carbon emissions. While changes to behavior around reducing waste and energy conservation at home were the most common actions taken, the largest reduction in participant-averaged carbon emissions came through transportation decisions. For example, while only 31% of participants reported purchasing a more gas-efficient car, this single action accounted for 18% of all carbon emission reductions observed. In contrast, while over 90% of participants reported that they recycle more often, the combined reduction in carbon emissions only accounted for 11% of the total reductions.

As shown in Fig 3 , the average reduction in carbon emissions based on the participant survey responses is 3.54 tons of CO 2 /year, with most participants between 2 and 5 tons of CO 2 /year. About 5% of students reported almost no change (0–1 ton of CO 2 /year), and about 10% reported between 6 and 8 tons of CO 2 /year. Of the four primary categories of carbon emission reductions, changes in transportation were responsible for 40% of the total carbon emission reductions, while waste reduction, food choices and home energy contributed 33%, 13% and 12% respectively of the achieved total carbon emission reductions.



4.1.2. Understanding how personal relevance and carbon emissions are related.

Given that one of the goals of the course is to help students develop a personal connection between global warming and their lives, we explore the connections between participant beliefs and total carbon emission reductions through analysis of grouped data. In Fig 4 , we show the relationship between individual carbon emission reductions with personal beliefs about how global warming will influence them or future generations. We find that participants who believe that global warming will harm them personally, or will harm future generations, have larger reductions in carbon emissions compared to participants who do not believe there will be a strong impact on them or future generations. Thus, it appears that in most cases, participants were at some level influenced by how they perceived the impact of global warming on their own well-being, or the well-being of future generations, when making personal decisions related to the environment.


The percentage of the total responses for that question is also given above each bar.


Further, of the participants who agreed (strongly agreed or agreed) to the statement, “I have personally experienced the effects of global warming.” their reductions in carbon emissions were 3.7 tons of CO 2 /year, while for the participants who did not agree with that statement (disagreed, strongly disagreed or neutral), their reductions were only 2.9 tons of CO 2 /year (see Fig 5 ).



4.2. Focus groups

Responses from focus group participants converged around two themes: the importance of daily decisions to mitigate their climate change impact and the importance of engaging their community through climate change communication. Examples of these themes from focus groups responses are provided below, together with relevant connection to the three predictor variables used to inform the course design.

4.2.1. Impact on daily decisions.

A hallmark of conversations with graduates from the course was the consideration of climate in daily decisions. Fundamentally, focus group participants recognized the pervasiveness of climate change. As Tara, a focus group participant, noted, “Almost every activity we choose can affect [climate change] in some way, whether we choose to take the bus or drive to work or whether we choose to buy food that’s grown on land that was cleared from rainforests….Since it is in every aspect of our life pretty much, that automatically makes it relevant to all those different aspects.” Other participants agreed and described daily actions that centered on transportation, waste and food choices. Melissa noted, “I think about it all the time…. Definitely how I think about and go about my days, making decisions, even just from using plastic.” And Elaine commented about buying a car after she paid off her student loans “I ended up choosing a Prius C for a lot of reasons. At the time it was pricey, but it just seemed energy efficient. It had what I was looking for while still being helpful for the environment.” These responses exemplify a common theme in the group—the knowledge of climate change gained in the course prompted them to think about the impact of their actions.

The focus group participants noted that they go out of their way to take action because they feel as if they are making a difference. Billy noted, “When everyone does something to mitigate climate change, it will have a huge impact.” Tara concurred, “Almost everything I do can affect the climate somehow. If you start realizing how everything ties together, then pretty much everything you do, every choice you make can affect it in some way.” She continued, “I think every small step does make a difference…. One little step at a time; it all adds up. I’d like to think we’re making a difference. I feel like I am when I contribute a little bit.” Participants suggested that the interdisciplinary focus of the course allowed them to see the connections between their actions and broader climate forcings.

Participant comments demonstrate that environmental actions are not just because of sacrifice but that people feel good about taking action. Lolitta explained, “So when we started the global climate change class, for a week we had to do something eco-friendly. I’m like okay, I’m gonna be a vegan. And I did it totally wrong. I just ate vegetables and fruits all day, and I was starving. But it got me to become vegan, and for a couple years I was. Now I’m a vegetarian, and I’ve stuck to it. I feel good about how I’m living my life, and I’m excited by all the changes that I’m making, and I will continue making these changes because they make me feel great.” Billy noted proudly that he acts because “it’s like a moral obligation.” Ultimately, participants concurred that daily actions matter, and they cited this belief as the reason they continue to take actions. Their comments suggest they are empowered to act because they see themselves as part of the solution.

4.2.2. Community engagement through communication.

Overall, focus group participants noted that this course helped them develop experience communicating with other people about their actions and why they are taking them. Participants cited the community action class project as a key element in their understanding of the impact of community engagement. Billy described the lasting impact of “the hands-on approach” of the project: “Those experiences, I think for me, I carry those longer than / more than being in the classroom…. Being with people, doing something that’s going to translate into what I have to do work-wise in the future, [the project was a] translatable experience to the workforce.” Melissa described the lasting impression of the project as a crucial aspect to seeing the impact of action: “It actually bridged the gap between the course and what the community itself is doing.”

Participants noted the impact of the course on life beyond the home. One focus group participant, Elaine, is a manager at Walmart, and she credited the course for her “awareness in an industry with high consumption…. It’s so interesting how much I’ve been able to use just from this course.” She noted her focus as a manager is how to “reduce your inventory, reduce the waste, sell what you need to.” Elaine views Walmart’s waste issues both as a climate issue and a management problem: “I see the huge amounts that they’re throwing away because they’re not managing their business correctly, because they’re not managing their production versus what they need, what they don’t. So that’s one of the things that I work on.” Elaine’s comments exemplify how many graduates of COMM 168 viewed the importance of taking action.

Billy noted the course explained how to make “big issues” like climate change “resonate with your audience… That’s what I do now.” He explains that in his job at the utility company, Pacific Gas and Electric, one of his roles is communicating about energy issues, “That’s my biggest takeaway from this class: messaging. [I now understand] the importance of communicating about climate change in a way where people who don’t have a background in that subject can understand.” Other participants concurred that the course made them experts in climate change, and they now have to think about how to communicate with people who don’t have such extensive knowledge.

Participants also noted the importance of communicating with others about the actions they take. Tara noted: “It doesn’t really help unless you try to bring it out there. If I only ever walk places, no one will ever know unless I try to let them know why I walk places…. If you’re going to make a point by breaking the rules, you first have to know the rules because otherwise it doesn’t mean anything. If I want to rebel by not using a car, I first have to know that everyone thinks using a car is a normal thing to do.” Participants agreed that talking about their own actions helped in discussing climate change issues with others.

The community action project was a key part of the course in giving students experience outside of class in creating change. It also gave them some agency over this issue. Participants described their attempts to make a difference, both in their personal and professional lives. Participants noted the community action project allowed them to see the importance of communication in the design of their projects. The focus group responses suggest that interdisciplinary education including aspects of communication can give students the skills and experience necessary to create change in their own communities.

The outcome of the themes that emerged from the focus groups are broadly aligned with the methodology outlined in the course design (Section 3) and as described in the conjecture map ( Fig 1 ) In particular, students noted a personal connection with climate change (ownership variable), and they demonstrated specific ways either through personal actions or through communication that they could take action (empowerment variable). The entry level variable, which describes a sensitivity or empathy for the environment, was present in some of the focus group remarks, but did not emerge as a central theme.

5. Educational approach

We describe a number of key design elements that stood out as critical to the success of the education program we developed and that have sustained student engagement over many years. These include a) connecting climate science to students’ lives, b) providing students with experience creating change in a community of their choice and c) creating a culture devoted to stewardship and action. We found that these elements of the course helped students to connect with the subject in ways that extended into their personal and professional lives, and are broadly aligned with some of the predictor variables that we used to design the course. These elements were not isolated from each other, or from other important elements of the course, including a solid focus on climate science, climate solutions and environmental communication. These elements are in line with the models suggested by other researchers, including personal relevance and empowerment [ 16 ]; [ 23 ]. We now review each of these elements in more detail to provide insights into how these ideas may be applied to other educational settings.

5.1. Connecting science to students’ lives

Various activities in the course were designed to help connect climate change with students’ lives and align with the ownership variable discussed in Fig 1 . One project asked students to reflect on how climate change would affect their personal and professional lives. Another project had students track their personal energy use, and then implement a plan to reduce their energy use in their home using data from their home smart meters. These elements appeared to have some lasting impact, as various focus group participants reflected on how the course materials affected their personal and professional lives.

In addition to the actions that were identified in the survey data, open-ended feedback also revealed that the course affected other major decisions, such as where to live and how many children to have. In fact, two of the participants mentioned their decisions to adopt a child or not to have children were influenced by the course. This implies that at least for some of the students, the course content and the implications of climate change affected their personal lives deeply. It appears that some of the high-impact actions identified by [ 30 ], such as having fewer children, did resonate with the COMM 168 students.

In a recent study by [ 23 ], a systematic review of the climate change education literature identified themes common in successful programs. One of the primary themes identified was a focus on making climate change personally relevant and meaningful for learners. It is noted that this is also a common practice in environmental education and science education, but as we found in our own work here, it can be made especially meaningful given the personal connection that climate change can have to students’ lives.

5.2. Creating change in a community of their choice

Another design element of the course was to provide students with real-world experience creating and implementing an action plan to reduce carbon emissions, an activity aligned with the empowerment variable. The Community Action Project (CAP) was the culminating experience where student teams competed to develop the most impactful community-based project. The goal of the CAP was to give students real-world experience developing solutions to climate change. It was our intention that through this experience, students would not only better understand some of the challenges associated with creating change but also gain confidence that change can happen through well-designed efforts. [ 45 ] found that using issue investigation and action training was an effective way to promote pro-environmental behavior. And [ 46 ] found that students were deeply affected by their service-learning course even years after the experience. The COMM 168 course was focused around the year-long CAP, and feedback from the focus groups shared how impactful the project was for some of the students, as a majority of the focus group participants mentioned the CAP as the most memorable part of the course. Our conclusion that the CAP promoted engagement and student empowerment has also been recognized in various other climate change education programs as a key element in creating effective learning experiences [ 23 ].

5.3. Creating a culture devoted to stewardship and action

  • Encouraging group discussions with different students: We did a lot of group work in class, and with 80–120 students per class, we took special efforts to mix students for their group work. This helped students work with new students and be exposed to new ideas. By giving students some challenging subjects to discuss (i.e., how does climate change affect their current or future lives), or challenging situations (i.e., during a UN simulation on climate change where students represented different countries negotiating a climate treaty), we gave students the opportunity to exchange personal ideas about climate. We felt this helped students see multiple views across the class, and if an emerging interest and dedication to climate change arose through the class, it could spread.
  • Faculty committed to climate action: The faculty who taught this course were all deeply committed to climate change solutions, and they were encouraged to share their own personal and professional journeys towards reducing carbon emissions. And because students got to know the faculty fairly well, given the course was taught over an academic year, students had the opportunity to connect with the faculty at a personal level. For example, when faculty reflected on their own personal challenges in reducing emissions associated with driving or eating, students could relate to this. Role models are important in creating social change, and we suggest that having professors committed to environmental solutions was also a factor in creating a social culture for the class that encouraged pro-environmental thinking and behavior. For example, one of the focus group participants mentioned that as a result of the class culture, her ownership of an SUV grew uncomfortable given her shifting connection to the environment. She admitted to deliberately concealing her vehicle type from the faculty, even though the faculty attempted to create a culture of acceptance without judgement. Later after graduating, this participant purchased a hybrid as her next vehicle. This is an example of the social norms that were established in the class that may have extended to students’ lives outside of school and over time.

6. Potential role of education on carbon emission reductions

Given the reductions in carbon emissions calculated in Section 4.1.1 (and shown in Fig 3 ), we now explore the potential role of education as a climate change mitigation strategy. We start by estimating the participant reductions in carbon emissions compared to a control group. The control group is created by using California’s per capita carbon emissions data as estimated by the California Air Resources Board (CARB) [ 49 ]. We choose to use California’s per capita carbon emissions for two reasons. First, we do not have a good way to access course participant’s prior behavior retrospectively, and second, we assume that behavior after graduating from the course could change as students become professionals resulting in a potential dramatic lifestyle change. The California per capita carbon emission data show that by 2014, per capita carbon emissions for the average Californian declined by 0.68 tons/year compared to 2009, the midpoint when students had graduated from SJSU. By contrast, the participants in COMM 168 reduced their per capita emissions by 3.54 tons/year. Thus, if we subtract the emission reductions for the average Californian (0.68) from our participants (3.54), we find that the net reduction above the average citizen is 2.86 tons/year (3.54–0.68 = 2.86).

We now use the net reduction in carbon emissions observed for graduates of COMM 168 to compare the potential role of education as a climate change mitigation strategy with other climate change mitigation strategies. For this comparison, we employ the methodology outlined in Project Drawdown, where 80 different technologies or strategies are evaluated based on the potential to cumulatively reduce carbon emissions by 2050 [ 50 ].

The following procedure and set of assumptions are used to calculate carbon emission reductions associated with climate change education, as shown in Fig 6 . We first assume that a modest investment in climate change education would allow students of secondary school age from middle and high income countries (where their carbon emissions are highest) to receive a specialized climate change education (i.e., using similar educational methodologies as we have described in this paper), and that students who receive this education would each reduce their carbon emissions by 2.86 tons of CO 2 /year (i.e., as in the COMM 168 course), for that year, and for each year following. Further, we assume that such a program would start small at 1 million students and grow by 13% per year until 2050, when the program reaches over 38 million participants. We use 2015 data from the United Nations Educational, Scientific and Cultural Organization (UNESCO) [ 51 ] to estimate the number of students of secondary school age from high income and upper middle income as 298 million. This allows us to estimate the percentage of students participating in this specialized climate change education program in 2020 and 2050, assuming the population of secondary students in these countries does not change.


The potential role of climate change education programs is calculated using the per student carbon reductions estimated from the COMM 168 course.


In Fig 6 , six of the solutions presented in Project Drawdown are compared with our own estimate for using education as a climate change mitigation strategy. For the solution scenarios developed by Project Drawdown, each of these represents ambitious and yet also technically and economically feasible plans for reducing carbon levels. Technical details and reference literature for all these solutions are presented at www.drawdown.org . As examples, the Rooftop Solar scenario grows the percentage of electricity generated by rooftop solar from 0.4% today to 7% by 2050, while the Electric Vehicles scenario grows the percentage of passenger miles from electric vehicles from less than 1% today to 16% by 2050. For the Climate Change Education scenario we assume that a) each student reduces their carbon emissions by 2.86 tons of CO 2 , similar to the COMM 168 course and b) the adoption of this type of education grows from less than 1% of all secondary students today to 16% of all secondary students by 2050 (note: the number of secondary students is restricted to only high income and upper-middle income countries where residents have higher carbon emissions).

The results of this comparison show that education, if designed appropriately, can potentially be as effective as other established climate change mitigation techniques. Based on the scenario we developed, the implementation of climate change education over a 30-year period (2020–2050) could reduce emissions by 18.8 GT of CO 2 eq, an amount that would rank in the top quarter (15 out of 80) of the presented solutions in Project Drawdown. Although at scale, the use of education as a climate change mitigation technique is still untested, our analysis suggests that if the educational approach is sound, and if we take the effort to measure the impact of education, we may realize the potential to reduce carbon emissions using education. We also acknowledge that although barriers to developing a successful large-scale climate change education program exist, significant social and political challenges exist with most large-scale solutions to climate change.

7. Uncertainties and study limitations

In the following section, we describe a number of uncertainties and study limitations that are important to the interpretation of the results. Although we believe the COMM 168 course provides unique insight into the long-term role that education can have on individual behaviors, especially given the lack of existing studies that look at how education can shape behavior over many years, we also acknowledge the potential limits of such a research design, and thus we are careful here to identify uncertainties and describe limitations in the study. The exposure of such uncertainties and limitations provides the research with a context for interpreting the results and also provides an avenue for researchers to undertake additional studies to investigate the impact that education can have on long-term behavior change.

7.1. Uncertainties

The study methodology and analysis include a number of assumptions that contribute to the uncertainties associated with this study, and these are discussed below.

Student enrollment.

Because the course is titled “Global Climate Change,” students interested in environmental issues may have self-selected into the course. These students may respond more favorably to the course design, and may be more willing to change their behavior in the future given their initial interest in the environment. Although the impact of incentives on bias is not clearly understood [ 52 ], the year-long course included a 3-unit incentive where a passing grade in the 9-unit course provided students with an additional 3 units of general education credit. We heard that many students reported that they signed up for the course because of the extra requirements satisfied. Further, we note that when this incentive was removed from the course design in 2014, the initial broad distribution of majors who enrolled in the class declined quite dramatically. In the earlier years with the 3-unit incentive (2007–2013), four colleges (i.e, Social Sciences, Humanities and the Arts, Business, and Health and Human Sciences) each had at least 10% of the registered students. However, once the 3-unit incentive was removed in 2014, only two colleges (i.e., Social Sciences, Humanities and the Arts) had significant enrollment (i.e., more than 10% of students), with the course now having more enrollment from Environmental Studies and Communication Studies. The 3-unit incentive thus appears to have been effective in drawing students from across campus, and this suggests that the course topic was not the only reason students enrolled in the course.

Energy calculations.

The household carbon footprint calculator was used to estimate how student responses would impact carbon emissions. Although the calculator has been used in a number of studies, various assumptions were made as described in Table 1 of S2 Text . It is clear that some of the carbon reductions attributed to the course experience may have inherent uncertainties. For example, actions such as carpooling regularly, making food choices to reduce emissions and buying energy-star appliances all suggest actions to reduce emissions, and yet the actual reduction amount depends on specifics of the action that are difficult to obtain without a more detailed survey tool. In contrast, the goal of this analysis was to document actions attributable to the course and develop a practical methodology for estimating the carbon reductions using the best tools available.

Behavior changes.

Another uncertainty that this research only partially uncovered was the motivation for the reported changes. Did participants make lifestyle changes because of environmental concerns or for other reasons, such as financial considerations or ethical concerns? In our focus group, participants reported that pro-environmental outcomes were the primary reason for their choices, but we do not know if this was also the case with all students. Further, without a more detailed survey, it is difficult to understand whether other factors (e.g., social circumstances) also contributed to these changes. This is one reason we chose to use the California per capita emission reduction as a control group, so that pro-environmental trends seen throughout California could be accounted for.

Other considerations.

We also acknowledge a number of other uncertainties in the design of this study. Participants were surveyed at least five years after taking the course, and we recognize the limits of human memory may skew some of their responses. There may be students who incorrectly remember aspects of the course, and this may have influenced some of our conclusions. This is in part why we chose to do a focus group to more accurately investigate aspects of the course that may have been important.

7.2. Study limitations

One limitation in this study is the lack of a control group or a pre-survey. We acknowledge that without such accompanying data, determining the precise relationship between students’ participation in the course and their current attitudes and behaviors is difficult. We did attempt to control for how pro-environmental behaviors in California have become more common over the last decade, but we do not have any data that measured student attitudes or behavior before taking the class. Although further studies should consider the various ways to measure changes in participant attitudes and behaviors, measuring such changes over many years remains a challenge.

Another limitation in the study is the potential for selection bias. Although we attempted to determine whether students self-selected into the course based on their environmental leanings or the 3-unit incentive, we do not have independent data to quantify the role that selection bias had on student enrollment. If students did select this course because of their initial interest in environmental stewardship, this could bias the outcomes of the study.

Another concern is related to biases in participant responses to survey and focus group questions. We acknowledge that a socially-agreeable response bias with regard to behaviors being attributed to the course may exist in the participant responses to surveys and focus group questions. Although we took measures in our survey design and focus group protocol to reduce such biases, it cannot be ruled out that such self-reporting response biases may be present and could influence the reliability of the results.

Finally, we recognize that among the uncertainties identified in section 7.1, none of them have been adequately quantified. Although some of these uncertainties, such as the reliability of the carbon footprint calculator and the related carbon emissions, probably would not influence the primary outcomes of the study, other uncertainties such as initial attitudes of participating students may have a larger influence on the study results.

As we have generally described, establishing linkages between an educational campaign and long-term behavior can be challenging. Other studies that attempt to establish causal links between education and environmental quality also faced similar challenges (e.g., [ 5 ]), and yet the insights gained from such work provide a strong motivation for environmental education and this type of research [ 7 ]; [ 53 ]. Our work is similar. Despite the limitations we have identified, our analysis provides important insights into understanding the role that well-designed climate change education can play on long-term attitudes and behavior.

8. Conclusions

The potential role of education on individual carbon emissions was studied using data from students who completed an intensive university course on climate change. Students were surveyed at least five years after having taken the course, and their responses were used to provide both qualitative and quantitative measures of the impact of the course on their attitudes and behavior regarding solutions to climate change. The university course was designed to be impactful, including various elements from the environmental education literature to engage students around personal and social activism. In open-ended feedback and the focus group interviews, students recounted how the course has changed their lives, both personally and professionally. Examples of personal changes included the type of car they drive and the type of food they eat. Examples of professional changes included how they create environmental benefits through their job. The results from the survey data also suggest that the course was impactful, even many years later. Student behavior related to waste decisions, home energy decisions, transportation and food choices all showed significant behavior change that was attributed to the COMM 168 course, and these changes were quantified using a reputable online carbon emissions calculator. The estimated reductions in carbon emissions attributed to the COMM 168 graduates are 3.54 tons/year, compared with the carbon emissions for an average California resident of 25.1 tons/year. It was found that the participants who had personally experienced the effects of global warming, or felt that global warming will harm them personally, had the largest reductions in carbon emissions. Although a number of studies have established links between educational programs and environmental quality, such as water or air quality [ 7 ], far fewer studies have established causal links between education and carbon emissions [ 5 ].

This study suggests that the design of the COMM 168 course provides elements of the three crucial factors that [ 17 ] identify as contributing to pro-environmental behavior: entry-level, ownership, and empowerment variables. Surveys and focus group interviews reveal that graduates of the course feel a lasting personal connection to the issue and have confidence in the success of their actions. This strong sense of personal obligation and the perceived individual agency to address climate change suggest that education that leverages these design elements including community engagement may provide a public benefit. The authors also note that social norms, established through a year-long course and emphasized through various classroom activities, also may have contributed to students’ pro-environmental attitudes and behaviors. However, while previous studies have demonstrated that factors such as having a personal connection (e.g., [ 23 ]) and perceived self-efficacy (e.g., [ 54 ]) can influence individual behaviors, we acknowledge that other factors are also likely important (e.g., [ 55 ]), and understanding how these factors contribute to individual behavior change is complex [ 39 ]; [ 56 ]. We also acknowledge that there may be cases where structural factors, such as size of home or distance of commute, may obscure the intentions of pro-environmental behavior [ 57 ].

The potential to use education as a climate change mitigation measure would be valuable and in line with other mitigation measures if such reductions as achieved in the COMM 168 course could be achieved in other classrooms. We illustrate this through comparisons with other climate change solutions, and show that at scale, climate change education can be as effective in reducing carbon emissions as other solutions such as rooftop solar or electric vehicles. The notion that education is an important part of responding to climate change is not novel (e.g., [ 29 ]; [ 58 ]), and yet rarely has it been quantified and measured [ 53 ]. This paper sheds light on how such measurements could be taken, and it offers a pedagogical insight for how to make education an effective climate change mitigation strategy.

At present, the authors are using similar design approaches to develop a comprehensive science curriculum focused around environmental stewardship and climate action (e.g., [ 59 ]; [ 60 ]) for middle schools. The Next Generation Science Standards now emphasize applying integrative science fields to solving real-world problems, and this serves as an ideal platform for applying the type of educational platform developed in COMM 168 towards a broader science curriculum for schools. The middle school science curriculum [ 61 ] is currently being used in a number of school districts in California, and studies examining changes in student attitudes and behavior will be reported in the future.

Supporting information

S1 text. survey instrument used for the graduates of the comm 168 course..


S2 Text. Procedure for estimating reductions in carbon emissions from the survey responses.


S3 Text. Focus group protocol.


S4 Text. COMM 168 syllabus.



We are grateful to the students involved in this study for their time and participation, and Dr. Elizabeth Walsh for her helpful suggestions on our data analysis. We also thank Liz Palfreyman for her help in gathering some of the student demographic data.

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  • v.33(2); Fall 2010

Climate Change: The Evidence and Our Options

Glaciers serve as early indicators of climate change. Over the last 35 years, our research team has recovered ice-core records of climatic and environmental variations from the polar regions and from low-latitude high-elevation ice fields from 16 countries. The ongoing widespread melting of high-elevation glaciers and ice caps, particularly in low to middle latitudes, provides some of the strongest evidence to date that a large-scale, pervasive, and, in some cases, rapid change in Earth's climate system is underway. This paper highlights observations of 20th and 21st century glacier shrinkage in the Andes, the Himalayas, and on Mount Kilimanjaro. Ice cores retrieved from shrinking glaciers around the world confirm their continuous existence for periods ranging from hundreds of years to multiple millennia, suggesting that climatological conditions that dominate those regions today are different from those under which these ice fields originally accumulated and have been sustained. The current warming is therefore unusual when viewed from the millennial perspective provided by multiple lines of proxy evidence and the 160-year record of direct temperature measurements. Despite all this evidence, plus the well-documented continual increase in atmospheric greenhouse gas concentrations, societies have taken little action to address this global-scale problem. Hence, the rate of global carbon dioxide emissions continues to accelerate. As a result of our inaction, we have three options: mitigation, adaptation, and suffering.

Climatologists, like other scientists, tend to be a stolid group. We are not given to theatrical rantings about falling skies. Most of us are far more comfortable in our laboratories or gathering data in the field than we are giving interviews to journalists or speaking before Congressional committees. Why then are climatologists speaking out about the dangers of global warming? The answer is that virtually all of us are now convinced that global warming poses a clear and present danger to civilization ( “Climate Change,” 2010 ).

That bold statement may seem like hyperbole, but there is now a very clear pattern in the scientific evidence documenting that the earth is warming, that warming is due largely to human activity, that warming is causing important changes in climate, and that rapid and potentially catastrophic changes in the near future are very possible. This pattern emerges not, as is so often suggested, simply from computer simulations, but from the weight and balance of the empirical evidence as well.


Figure 1 shows northern hemisphere temperature profiles for the last 1,000 years from a variety of high-resolution climate recorders such as glacier lengths ( Oerlemans, 2005 ), tree rings ( Briffa, Jones, Schwerngruber, Shiyatov, & Cook, 2002 ; Esper, Cook, & Schweingruber, 2002 ), and combined sources that include some or all of the following: tree rings, sediment cores, ice cores, corals, and historical records ( Crowley & Lowery, 2000 ; Jones, Briffa, Barnett, & Tett, 1998 ; Mann, Bradley, & Hughes, 1999 ; Moberg, Sonechkin, Holmgrem, Datsenko, & Karlen, 2005 ). The heavy gray line is a composite of all these temperatures ( Mann & Jones, 2003 ), and the heavy black line depicts actual thermometer readings back to 1850 (see National Research Council, 2006 , for a review of surface temperature reconstructions). Although the various curves differ from one another, their general shapes are similar. Each data source shows that average northern hemisphere temperatures remained relatively stable until the late 20th century. It is the agreement of these diverse data sets and the pattern that make climatologists confident that the warming trend is real.

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A variety of temperature records over the last 1,000 years, based on a variety of proxy recorders such as tree rings, ice cores, historical records, instrumental data, etc., shows the extent of the recent warming. The range of temperature projected by Meehl et al. (2007) to 2100 AD is shown by the shaded region, and the average of the range is depicted by the filled circle.

Because these temperature numbers are based on northern hemisphere averages, they do not reflect regional, seasonal, and altitudinal variations. For example, the average temperature in the western United States is rising more rapidly than in the eastern part of the country, and on average winters are warming faster than summers ( Meehl, Arblaster, & Tebaldi, 2007 ). The most severe temperature increases appear to be concentrated in the Arctic and over the Antarctic Peninsula as well as within the interior of the large continents. This variability complicates matters, and adds to the difficulty of convincing the public, and even scientists in other fields, that global warming is occurring. Because of this, it may be useful to examine another kind of evidence: melting ice.

Retreat of Mountain Glaciers

The world's mountain glaciers and ice caps contain less than 4% of the world's ice cover, but they provide invaluable information about changes in climate. Because glaciers are smaller and thinner than the polar ice sheets, their ratio of surface area to volume is much greater; thus, they respond more quickly to temperature changes. In addition, warming trends are amplified at higher altitudes where most glaciers are located ( Bradley, Keimig, Diaz, & Hardy, 2009 ; Bradley, Vuille, Diaz, & Vergara, 2006 ). Thus, glaciers provide an early warning system of climate change; they are our “canaries in the coal mine.”

Consider the glaciers of Africa's Mount Kilimanjaro ( Figure 2 ). Using a combination of terrestrial photogrammetric maps, satellite images, and aerial photographs, we have determined that the ice fields on Kibo, the highest crater on Kilimanjaro, have lost 85% of their coverage since 1912 ( Thompson, Brecher, Mosley-Thompson, Hardy, & Mark, 2009 ).

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The retreat of glaciers on Mount Kilimanjaro can be seen in the photographs from 1912, 1970, 2000, and 2006; from 1912 to 2006, 85% of the ice has disappeared.

Figure 3 shows a series of aerial photographs of Furtwängler glacier, in the center of Kibo crater, taken between 2000 and 2007, when the glacier split into two sections. As Furtwängler recedes, it is also thinning rapidly, from 9.5 m in 2000 to 4.7 m in 2009 (for more images of Furtwängler's retreat, see http://www.examiner.com/examiner/x-10722-Orlando-Science-Policy-Examiner∼y2009m11d2-Mt-Kilimanjaros-Furtwängler-Glacier-in-retreat ). If you connect the dots on the changes seen to date and assume the same rate of loss in the future, within the next decade many of the glaciers of Kilimanjaro, a Swahili word meaning “shining mountain,” will have disappeared.

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Deterioration of the Furtwängler glacier in the center of Kibo crater on Mount Kilimanjaro. Since 2000 the ice field has decreased in size and thickness and has divided in two.

The Quelccaya ice cap, which is located in southern Peru adjacent to the Amazon Basin, is the largest tropical ice field on Earth. Quelccaya has several outlet glaciers, glaciers that extend from the edges of an ice cap like fingers from a hand. The retreat of one of these, Qori Kalis, has been studied and photographed since 1963. At the beginning of this study, Qori Kalis extended 1,200 m out from the ice cap, and there was no melt water at the end ( Figure 4 , map top left). By the summer of 2008, Qori Kalis had retreated to the very edge of Quelccaya, leaving behind an 84-acre lake, 60 m deep. Over the years, a boulder near the base camp has served as a benchmark against which to record the changes in the position of the edge of the ice. In 1977 the ice was actually pushing against the boulder ( Figure 5 , top), but by 2006 a substantial gap had appeared and been filled by a lake ( Figure 5 , bottom). Thus, the loss of Quelccaya's ice is not only on the Qori Kalis glacier but also on the margin of the ice cap itself. Since 1978, about 25% of this tropical ice cap has disappeared.

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Retreat of the Qori Kalis outlet glacier on the Quelccaya ice cap. Each line shows the extent of the ice. The photos along the bottom provide a pictorial history of the melting of the Qori Kalis outlet glacier and the formation of a lake. The retreat of Qori Kalis is similar to the loss of several Peruvian glaciers, as shown in the graph insert.

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Top: photo taken in 1978 shows a margin of the Quelccaya ice cap pushing against a boulder. Bottom: the same margin is shown in a 2005 photo. The ice has receded and has been replaced by a small lake. The boulder shown in the top photo is located in the center of the white circle to the right.

The Himalayan Mountains are home to more than 15,000 glaciers. Unfortunately, only a few of these glaciers have been monitored over an extended period, so reliable ground observations that are crucial for determining regional retreat rates do not yet exist. However, a recent study of an ice core from the Naimona'nyi glacier in the southwestern Himalayas ( Kehrwald et al., 2008 ) shows that ice is disappearing from the top of the glacier, as shown by the lack of the radioactive bomb layers from the 1950s and early 1960s that appear in all Tibetan and Himalayan ice core records ( Thompson, 2000 ; Thompson et al., 1990 , 1997 , 2006 ).

Glaciologists at the Institute of Tibetan Plateau Research in Beijing have been monitoring 612 glaciers across the High Asian region since 1980. These scientists found that from 1980 to 1990, 90% of these glaciers were retreating; from 1990 to 2005, the proportion of retreating glaciers increased to 95% ( Yao, Pu, Lu, Wang, & Yu, 2007 ).

A study of 67 glaciers in Alaska from the mid-1950s to the mid-1990s shows that all are thinning ( Arendt, Echelmeyer, Harrison, Lingle, & Valentine, 2002 ). In northern Alaska's Brooks Range, 100% of the glaciers are in retreat, and in southeastern Alaska 98% are shrinking ( Molnia, 2007 ). Glacier National Park in Montana contained more than 100 glaciers when it was established in 1910. Today, just 26 remain, and at the current rate of decrease it is estimated that by 2030 there will be no glaciers in Glacier National Park ( Hall & Fagre, 2003 ). The oldest glacier photos come from the Alps. Ninety-nine percent of the glaciers in the Alps are retreating, and 92% of Chile's Andean glaciers are retreating ( Vince, 2010 ).

The pattern described here is repeated around the world. Mountain glaciers nearly everywhere are retreating.

Loss of Polar Ice

Satellite documentation of the area covered by sea ice in the Arctic Ocean extends back three decades. This area, measured each September, decreased at a rate of about 8.6% per decade from 1979 to 2007. In 2007 alone, 24% of the ice disappeared. In 2006 the Northwest Passage was ice free for the first time in recorded history.

As noted earlier, polar ice sheets are slower to respond to temperature rise than the smaller mountain glaciers, but they, too, are melting. The Greenland ice sheet has also experienced dramatic ice melt in recent years. There has been an increase in both the number and the size of lakes in the southern part of the ice sheet, and crevices can serve as conduits (called moulins) that transport meltwater rapidly into the glacier. Water has been observed flowing through these moulins down to the bottom of the ice sheet where it acts as a lubricant that speeds the flow of ice to the sea ( Das et al., 2008 ; Zwally et al., 2002 ).

The ice in Antarctica is also melting. The late John Mercer, a glacial geologist at The Ohio State University, long ago concluded that the first evidence of global warming due to increasing carbon dioxide (CO 2 ) would be the breakup of the Antarctic ice shelves ( Mercer, 1978 ). Mean temperatures on the Antarctic Peninsula have risen 2.5° C (4.5° F) in the last 50 years, resulting in the breakup of the ice shelves in just the way Mercer predicted. One of the most rapid of these shelf deteriorations occurred in 2002, when the Larsen B, a body of ice over 200 m deep that covered an area the size of Rhode Island, collapsed in just 31 days (see images http://earthobservatory.nasa.gov/IOTD/view.php?id = 2351). An ice shelf is essentially an iceberg attached to land ice. Just as an ice cube does not raise the water level in a glass when it melts, so a melting ice shelf leaves sea levels unchanged. But ice shelves serve as buttresses to glaciers on land, and when those ice shelves collapse it speeds the flow of the glaciers they were holding back into the ocean, which causes sea level to rise rapidly.

Just days before this paper went to press, a giant ice island four times the size of Manhattan broke off the Petermann glacier in Greenland. This event alone does not prove global climate change, because half of the ice loss from Greenland each year comes from icebergs calving from the margins. It is the fact that this event is part of a long-term trend of increasing rates of ice loss, coupled with the fact that temperature is increasing in this region at the rate of 2° C (3.6° F) per decade, that indicates that larger scale global climate change is underway.

The loss of ice in the Arctic and Antarctic regions is especially troubling because these are the locations of the largest ice sheets in the world. Of the land ice on the planet, 96% is found on Greenland and Antarctica. Should all this ice melt, sea level would rise over 64 m ( Church et al., 2001 ; Lemke et al., 2007 ), and of course the actual sea level would be much higher due to thermal expansion of the world's oceans as they warm.

Although research shows some variability in the rate of ice loss, it is clear that mountain glaciers and polar ice sheets are melting, and there is no plausible explanation for this but global warming. Add to this the laboratory evidence and the meteorological measurements, and the case for global warming cannot be denied. So what causes global temperatures to rise?


Climatologists strive to reconstruct past climate variations on regional and global scales, but they also try to determine the mechanisms, called forcers , that drive climate change. Climatologists recognize two basic categories of forcers. Natural forcers are recurring processes that have been around for millions of years; anthropogenic forcers are more recent processes caused by human activity.

One familiar natural forcer is the earth's orbit around the sun, which gives us our seasons. In the northern hemisphere, June is warm because the sun's rays fall more directly on it, and the sun appears high in the sky; in the southern hemisphere, June is cool because the sun's rays hit the earth at a deep angle, and the sun appears low in the sky.

Less obvious natural forcers include short- and long-term changes in the atmosphere and ocean. For example, when Mount Pinatubo erupted in the Philippines in 1991, it spewed millions of tons of sulfuric gases and ash particles high into the atmosphere, blocking the sun's rays. This lowered global temperatures for the next few years. Another natural forcer is the linked oceanic and atmospheric system in the equatorial Pacific Ocean known as the El Niño-Southern Oscillation (ENSO). ENSO occurs every 3 to 7 years in the tropical Pacific and brings warm, wet weather to some regions and cool, dry weather to other areas.

Other natural forcers include periodic changes in energy from the sun. These include the 11- to 12-year sunspot cycle and the 70- to 90-year Wolf-Gleissberg cycle, a modulation of the amplitude of the 11-year solar cycle. These changes in solar energy can affect atmospheric temperature across large regions for hundreds of years and may have caused the “medieval climate anomaly” in the northern hemisphere that lasted from about 1100 AD to 1300 AD. Solar cycles may also have played a role in the cause of the “little ice age” in North America and Europe during the 16th to 19th centuries. These changes in climate, which are often cited by those who dismiss global warming as a normal, cyclical event, affected large areas, but not the Earth as a whole. The medieval climate anomaly showed warmth that matches or exceeds that of the past decade in some regions, but it fell well below recent levels globally ( Mann et al., 2009 ).

The most powerful natural forcers are variations in the orbit of the Earth around the Sun, which last from 22,000 to 100,000 years. These “orbital forcings” are partly responsible for both the ice ages (the glacial periods during which large regions at high and midddle latitudes are covered by thick ice sheets), and for the warm interglacial periods such as the present Holocene epoch which began about 10,000 years ago.

There is consensus among climatologists that the warming trend we have been experiencing for the past 100 years or so cannot be accounted for by any of the known natural forcers. Sunspot cycles, for example, can increase the sun's output, raising temperatures in our atmosphere. We are seeing a temperature increase in the troposphere, the lower level of our atmosphere, and a temperature decrease in the stratosphere, the upper level. But this is the exact opposite of what we would get if increased solar energy were responsible. Similarly, global temperatures have increased more at night than during the day, again the opposite of what would occur if the sun were driving global warming. In addition, temperatures have risen more in winter than in summer. This, too, is the opposite of what would be expected if the sun were responsible for the planet's warming. High latitudes have warmed more than low latitudes, and because we get more radiation from the sun at low latitudes, we again would expect the opposite if the sun were driving these changes. Thus, changes in solar output cannot account for the current period of global warming ( Meehl et al., 2007 ). ENSO and other natural forcers also fail to explain the steady, rapid rise in the earth's temperature. The inescapable conclusion is that the rise in temperature is due to anthropogenic forces, that is, human behavior.

The relatively mild temperatures of the past 10,000 years have been maintained by the greenhouse effect, a natural phenomenon. As orbital forcing brought the last ice age to an end, the oceans warmed, releasing CO 2 into the atmosphere, where it trapped infrared energy reflected from the earth's surface. This warmed the planet. The greenhouse effect is a natural, self-regulating process that is absolutely essential to sustain life on the planet. However, it is not immutable. Change the level of greenhouse gases in the atmosphere, and the planet heats up or cools down.

Greenhouse gases are captured in ice, so ice cores allow us to see the levels of greenhouse gases in ages past. The longest ice core ever recovered (from the European Project for Ice Coring in Antarctica) takes us 800,000 years back in time, and includes a history of CO 2 and methane levels preserved in bubbles in the ice ( Loulergue et al., 2008 ; Lüthi et al., 2008 ). The CO 2 and methane curves illustrated in Figure 6 show that the modern levels of these gases are unprecedented in the last 800 millennia.

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Concentrations of carbon dioxide (CO 2 ) and methane (CH 4 ) over the last 800,000 years (eight glacial cycles) from East Antarctic ice cores. Data from Loulergue et al. (2008) and Lüthi et al. (2008) . The current concentrations of CO 2 and CH 4 are also shown ( Forster et al., 2007 ).

Globally, CO 2 concentrations have varied between 180 and 190 parts per million per volume (ppmv) during glacial (cold) periods and between 270 and 290 ppmv during interglacial (warm) periods. However, since the onset of the Industrial Revolution, when fossil fuel use (chiefly coal and oil) began to burgeon, CO 2 concentration has increased about 38% over the natural interglacial levels ( Forster et al., 2007 ). Between 1975 and 2005, CO 2 emissions increased 70%, and between 1999 and 2005 global emissions increased 3% per year ( Marland, Boden, & Andres, 2006 ). As of this writing, the CO 2 concentration in the atmosphere is 391 ppmv (Mauna Loa CO 2 annual mean data from the National Oceanic and Atmospheric Administration, 2010 ), a level not seen at any time in 800,000 years. Climatologists have identified no natural forcers that could account for this rapid and previously unseen rise in CO 2 .

Methane raises temperature even more than CO 2 , and the amount of methane in the atmosphere, like that of CO 2 , is also at a level not seen in 800 millennia. Two thirds of current emissions of methane are by-products of human activity, things like the production of oil and natural gas, deforestation, decomposition of garbage and sewage, and raising farm animals.

Many people find it difficult to believe that human activity can affect a system as large as Earth's climate. After all, we are so tiny compared to the planet. But every day we tiny human beings drive cars; watch television; turn on lamps; heat or cool our houses and offices; eat food transported to us by planes, ships, and trucks; clear or burn forests; and behave in countless other ways that directly or indirectly release greenhouse gases into the air. Together, we humans emitted eight billion metric tons of carbon to our planet's atmosphere in 2007 alone ( Boden, Marland, & Andres, 2009 ). (CO 2 weighs 3.66 times more than carbon; that means we released 29.3 billion metric tons of CO 2 .) The evidence is overwhelming that human activity is responsible for the rise in CO 2 , methane, and other greenhouse gas levels, and that the increase in these gases is fueling the rise in mean global temperature.

A global temperature rise of a few degrees may not seem such a bad thing, especially to people living in harsh, cold climates. But global warming does not mean merely that we will trade parkas for T-shirts or turn up the air conditioning. A warming planet is a changing planet, and the changes will have profound consequences for all species that live on it, including humans. Those changes are not just something our children and grandchildren will have to deal with in the future; they are taking place now, and are affecting millions of people.


One effect of global warming that everyone has heard about is a rise in sea levels. About half of this rise is due to thermal expansion: Ocean temperatures are rising, and as water warms it expands. Put a nearly full cup of water in a microwave and heat it, and the water will spill over the cup.

In addition to thermal expansion, the oceans are rising because ice is melting, and most of that water inevitably finds its way to the sea. So far, most of that water has come from mountain glaciers and ice caps ( Meier et al., 2007 ). As global temperatures increase, sea level rise will mainly reflect polar ice melt. So far, ocean rise has been measured in millimeters, but there is enough water in the Greenland ice sheet alone to raise sea levels by about 7 m, West Antarctica over 5 m, and East Antarctica about 50 m ( Lemke et al., 2007 ). If the Earth were to lose just 8% of its ice, the consequences for some coastal regions would be dramatic. The lower part of the Florida peninsula and much of Louisiana, including New Orleans, would be submerged, and low-lying cities, including London, New York, and Shanghai, would be endangered (to see the effects of various magnitudes of sea level rise in the San Francisco Bay area, go to http://cascade.wr.usgs.gov/data/Task2b-SFBay/data.shtm ).

Low-lying continental countries such as the Netherlands and much of Bangladesh already find themselves battling flooding more than ever before. Many small island nations in the western Pacific (e.g., Vanuatu) are facing imminent destruction as they are gradually overrun by the rising ocean. Indonesia is an island nation, and many of its 17,000 islands are just above sea level. At the 2007 United Nations Climate Change Conference in Bali, Indonesian environmental minister Rachmat Witoelar stated that 2,000 of his country's islands could be lost to sea level rise by 2030. At current rates of sea level rise, another island nation, the Republic of Maldives, will become uninhabitable by the end of the century ( http://unfcc.int/resource/docs/napa/mdv01.pdf ). In 2008, the president of that country, Mohamed Nasheed, announced that he was contemplating moving his people to India, Sri Lanka, and Australia ( Schmidle, 2009 ). One of the major effects of continued sea level rise will be the displacement of millions of people. Where millions of climate refugees will find welcome is unclear. The migration of large numbers of people to new territories with different languages and cultures will be disruptive, to say the least.

In addition to the danger of inundation, rising sea levels bring salt water into rivers, spoil drinking wells, and turn fertile farmland into useless fields of salty soil. These effects of global warming are occurring now in places like the lowlands of Bangladesh ( Church et al., 2001 ).

People on dry land need the fresh water that is running into the sea. In the spring, melting ice from mountain glaciers, ice caps, and snowfields furnish wells and rivers that provide fresh water for drinking, agriculture, and hydroelectric power. For example, in the dry season, people in large areas of India, Nepal, and southern China depend on rivers fed by Himalayan glaciers. The retreat of these glaciers threatens the water supply of millions of people in this part of the world. Peru relies on hydroelectric power for 80% of its energy ( Vergara et al., 2007 ), a significant portion of which comes from mountain streams that are fed by mountain glaciers and ice fields. In Tanzania, the loss of Mount Kilimanjaro's fabled ice cover would likely have a negative impact on tourism, which is the country's primary source of foreign currency. The glaciers and snow packs in the Rocky Mountains are essential for farming in California, one of the world's most productive agricultural areas.

Global warming is expanding arid areas of the Earth. Warming at the equator drives a climate system called the Hadley Cell. Warm, moist air rises from the equator, loses its moisture through rainfall, moves north and south, and then falls to the Earth at 30° north and south latitude, creating deserts and arid regions. There is evidence that over the last 20 years the Hadley Cell has expanded north and south by about 2° latitude, which may broaden the desert zones ( Seidel, Fu, Randel, & Reichler, 2008 ; Seidel & Randel, 2007 ). If so, droughts may become more persistent in the American Southwest, the Mediterranean, Australia, South America, and Africa.

Global warming can also have effects that seem paradoxical. Continued warming may change ocean currents that now bring warm water to the North Atlantic region, giving it a temperate climate. If this happens, Europe could experience a cooling even as other areas of the world become warmer.

Accelerating Change

It is difficult to assess the full effects of global warming, and harder still to predict future effects. Climate predictions are made with computer models, but these models have assumed a slow, steady rate of change. Our best models predict a temperature rise in this century of between 2.4° and 4.5° C (4.3° and 8.1° F), with an average of about 3° C (5.4° F; Meehl et al., 2007 ; Figure 1 ). But these models assume a linear rise in temperature. Increasingly, computer models have underestimated the trends because, in fact, the rate of global temperature rise is accelerating. The average rise in global temperature was 0.11° F per decade over the last century ( National Oceanic and Atmospheric Administration, 2009 ). Since the late 1970s, however, this rate has increased to 0.29° F per decade, and 11 of the warmest years on record have occurred in the last 12 years. May, 2010, was the 303rd consecutive month with a global temperature warmer than its 20th-century average ( National Oceanic and Atmospheric Administration, 2010 ).

The acceleration of global temperature is reflected in increases in the rate of ice melt. From 1963 to 1978, the rate of ice loss on Quelccaya was about 6 m per year. From 1991 to 2006, it averaged 60 m per year, 10 times faster than the initial rate ( Thompson et al., 2006 ). A recent paper by Matsuo and Heki (2010) reports uneven ice loss from the high Asian ice fields, as measured by the Gravity Recovery and Climate Experiment satellite observations between 2003 and 2009. Ice retreat in the Himalayas slowed slightly during this period, and loss in the mountains to the northwest increased markedly over the last few years. Nevertheless, the average rate of ice melt in the region was twice the rate of four decades before. In the last decade, many of the glaciers that drain Greenland and Antarctica have accelerated their discharge into the world's oceans from 20% to 100% ( Lemke et al., 2007 ).

Increasing rates of ice melt should mean an increasing rate of sea level rise, and this is in fact the case. Over most of the 20th century, sea level rose about 2 mm per year. Since 1990, the rate has been about 3 mm per year.

So, not only is Earth's temperature rising, but the rate of this change is accelerating. This means that our future may not be a steady, gradual change in the world's climate, but an abrupt and devastating deterioration from which we cannot recover.

Abrupt Climate Change Possible

We know that very rapid change in climate is possible because it has occurred in the past. One of the most remarkable examples was a sudden cold, wet event that occurred about 5,200 years ago, and left its mark in many paleoclimate records around the world.

The most famous evidence of this abrupt weather change comes from Otzi, the “Tyrolean ice man” whose remarkably preserved body was discovered in the Eastern Alps in 1991 after it was exposed by a melting glacier. Forensic evidence suggests that Otzi was shot in the back with an arrow, escaped his enemies, then sat down behind a boulder and bled to death. We know that within days of Otzi's dying there must have been a climate event large enough to entomb him in snow; otherwise, his body would have decayed or been eaten by scavengers. Radiocarbon dating of Otzi's remains revealed that he died around 5,200 years ago ( Baroni & Orombelli, 1996 ).

The event that preserved Otzi could have been local, but other evidence points to a global event of abrupt cooling. Around the world organic material is being exposed for the first time in 5,200 years as glaciers recede. In 2002, when we studied the Quelccaya ice cap in southern Peru, we found a perfectly preserved wetland plant. It was identified as Distichia muscoides , which today grows in the valleys below the ice cap. Our specimen was radiocarbon dated at 5,200 years before present ( Thompson et al., 2006 ). As the glacier continues to retreat, more plants have been collected and radiocarbon dated, almost all of which confirm the original findings ( Buffen, Thompson, Mosley-Thompson, & Huh, 2009 ).

Another record of this event comes from the ice fields on Mount Kilimanjaro. The ice dating back 5,200 years shows a very intense, very sudden decrease in the concentration of heavy oxygen atoms, or isotopes, in the water molecules that compose the ice ( Thompson et al., 2002 ). Such a decrease is indicative of colder temperatures, more intense snowfall, or both.

The Soreq Cave in Israel contains speleothems that have produced continuous climate records spanning tens of thousands of years. The record shows that an abrupt cooling also occurred in the Middle East about 5,200 years ago, and that it was the most extreme climatic event in the last 13,000 years ( Bar-Matthews, Ayalon, Kaufman, & Wasserburg, 1999 ).

One way that rapid climate change can occur is through positive feedback. In the physical sciences, positive feedback means that an event has an effect which, in turn, produces more of the initial event. The best way to understand this phenomenon as it relates to climate change is through some very plausible examples:

Higher global temperatures mean dryer forests in some areas, which means more forest fires, which means more CO 2 and ash in the air, which raises global temperature, which means more forest fires, which means …

Higher global temperatures mean melting ice, which exposes darker areas (dirt, rock, water) that reflect less solar energy than ice, which means higher global temperatures, which means more melting ice, which means …

Higher global temperatures mean tundra permafrost melts, releasing CO 2 and methane from rotted organic material, which means higher global temperature, which means more permafrost melting, which means …

Positive feedback increases the rate of change. Eventually a tipping point may be reached, after which it could be impossible to restore normal conditions. Think of a very large boulder rolling down a hill: When it first starts to move, we might stop it by pushing against it or wedging chocks under it or building a barrier, but once it has reached a certain velocity, there is no stopping it. We do not know if there is a tipping point for global warming, but the possibility cannot be dismissed, and it has ominous implications. Global warming is a very, very large boulder.

Even if there is no tipping point (or we manage to avoid it), the acceleration of warming means serious trouble. In fact, if we stopped emitting greenhouse gases into the atmosphere tomorrow, temperatures would continue to rise for 20 to 30 years because of what is already in the atmosphere. Once methane is injected into the troposphere, it remains for about 8 to 12 years ( Prinn et al., 1987 ). Carbon dioxide has a much longer residence: 70 to 120 years. Twenty percent of the CO 2 being emitted today will still affect the earth's climate 1,000 years from now ( Archer & Brovkin, 2008 ).

If, as predicted, global temperature rises another 3° C (5.4° F) by the end of the century, the earth will be warmer than it has been in about 3 million years ( Dowsett et al., 1994 ; Rahmstorf, 2007 ). Oceans were then about 25 m higher than they are today. We are already seeing important effects from global warming; the effects of another 3° C (5.4° F) increase are hard to predict. However, such a drastic change would, at the very least, put severe pressure on civilization as we know it.


Global warming is here and is already affecting our climate, so prevention is no longer an option. Three options remain for dealing with the crisis: mitigate, adapt, and suffer.

Mitigation is proactive, and in the case of anthropogenic climate change it involves doing things to reduce the pace and magnitude of the changes by altering the underlying causes. The obvious, and most hotly debated, remedies include those that reduce the volume of greenhouse gas emissions, especially CO 2 and methane. Examples include not only using compact fluorescent lightbulbs, adding insulation to our homes, and driving less, but societal changes such as shutting down coal-fired power plants, establishing a federal carbon tax (as was recently recommended by the National Academy of Sciences), and substantially raising minimum mileage standards on cars ( National Research Council, 2010 ). Another approach to mitigation that has received widespread attention recently is to enhance the natural carbon sinks (storage systems) through expansion of forests. Some have suggested various geo-engineering procedures (e.g., Govindasamy & Caldeira, 2000 ; Wigley, 2006 ). One example is burying carbon in the ocean or under land surfaces ( Brewer, Friederich, Peltzer, & Orr, 1999 ). Geo-engineering ideas are intriguing, but some are considered radical and may lead to unintended negative consequences ( Parkinson, 2010 ).

Adaptation is reactive. It involves reducing the potential adverse impacts resulting from the by-products of climate change. This might include constructing sea barriers such as dikes and tidal barriers (similar to those on the Thames River in London and in New Orleans), relocating coastal towns and cities inland, changing agricultural practices to counteract shifting weather patterns, and strengthening human and animal immunity to climate-related diseases.

Our third option, suffering, means enduring the adverse impacts that cannot be staved off by mitigation or adaptation. Everyone will be affected by global warming, but those with the fewest resources for adapting will suffer most. It is a cruel irony that so many of these people live in or near ecologically sensitive areas, such as grasslands (Outer Mongolia), dry lands (Sudan and Ethiopia), mountain glaciers (the Quechua of the Peruvian Andes), and coastal lowlands (Bangledesh and the South Sea island region). Humans will not be the only species to suffer.

Clearly mitigation is our best option, but so far most societies around the world, including the United States and the other largest emitters of greenhouse gases, have done little more than talk about the importance of mitigation. Many Americans do not even accept the reality of global warming. The fossil fuel industry has spent millions of dollars on a disinformation campaign to delude the public about the threat, and the campaign has been amazingly successful. (This effort is reminiscent of the tobacco industry's effort to convince Americans that smoking poses no serious health hazards.) As the evidence for human-caused climate change has increased, the number of Americans who believe it has decreased. The latest Pew Research Center (2010) poll in October, 2009, shows that only 57% of Americans believe global warming is real, down from 71% in April, 2008.

There are currently no technological quick fixes for global warming. Our only hope is to change our behavior in ways that significantly slow the rate of global warming, thereby giving the engineers time to devise, develop, and deploy technological solutions where possible. Unless large numbers of people take appropriate steps, including supporting governmental regulations aimed at reducing greenhouse gas emissions, our only options will be adaptation and suffering. And the longer we delay, the more unpleasant the adaptations and the greater the suffering will be.

Sooner or later, we will all deal with global warming. The only question is how much we will mitigate, adapt, and suffer.


This paper is based on the Presidential Scholar's Address given at the 35th annual meeting of the Association for Behavior Analysis International, Phoenix, Arizona. I am grateful to Bill Heward for inviting me to give the address. I thank Mary Davis for her help editing the text and figures. I wish to thank all the field and laboratory team members from the Byrd Polar Research Center who have worked so diligently over the years. I am especially indebted to the hard work of our current research team: Ellen Mosley-Thompson, Henry Brecher, Mary Davis, Paolo Gabrielli, Ping-Nan Lin, Matt Makou, Victor Zagorodnov, and all of our graduate students. Funding for our research over the years has been provided by the National Science Foundation's Paleoclimate Program, the National Oceanic and Atmospheric Administration's Paleoclimatology and Polar Programs, the National Aeronautic and Space Administration, Gary Comer Foundation, and The Ohio State University's Climate, Water and Carbon Program. This is Byrd Polar Research Center Publication 1402.

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Lesson of the Day

Explore 7 Climate Change Solutions

In this lesson, students will use a jigsaw activity to learn about some of the most effective strategies and technologies that can help head off the worst effects of global warming.

Migrating cranes flying near Straussfurt, Germany. Climate change and biodiversity are “more deeply intertwined than originally thought,” one of the leaders of a new report said. <a href="https://www.nytimes.com/2021/06/10/climate/biodiversity-collapse-climate-change.html">Related Article</a>

By Natalie Proulx

Lesson Overview

Earlier this summer, a report issued by the Intergovernmental Panel on Climate Change , a body of scientists convened by the United Nations, found that some devastating impacts of global warming were unavoidable. But there is still a short window to stop things from getting even worse.

This report will be central at COP26 , the international climate summit where about 20,000 heads of state, diplomats and activists are meeting in person this week to set new targets for cutting emissions from coal, oil and gas that are heating the planet.

In this lesson, you will learn about seven ways we can slow down climate change and head off some of its most catastrophic consequences while we still have time. Using a jigsaw activity , you’ll become an expert in one of these strategies or technologies and share what you learn with your classmates. Then, you will develop your own climate plan and consider ways you can make a difference based on your new knowledge.

What do you know about the ways the world can slow climate change? Start by making a list of strategies, technologies or policies that could help solve the climate crisis.

Which of your ideas do you think could have the biggest impact on climate change? Circle what you think might be the top three.

Now, test your knowledge by taking this 2017 interactive quiz:

academic essay on climate change

How Much Do You Know About Solving Global Warming?

A new book presents 100 potential solutions. Can you figure out which ones are top ranked?

After you’ve finished, reflect on your own in writing or in discussion with a partner:

What solutions to climate change did you learn about that you didn’t know before?

Were you surprised by any of the answers in the quiz? If so, which ones and why?

What questions do you still have about solving climate change?

Jigsaw Activity

As you learned in the warm-up, there are many possible ways to mitigate the worst effects of climate change. Below we’ve rounded up seven of the most effective solutions, many of which you may have been introduced to in the quiz above.

In this jigsaw activity, you’ll become an expert in one of the climate solutions listed below and then present what you learned to your classmates. Teachers may assign a student or small group to each topic, or allow them to choose. Students, read at least one of the linked articles on your topic; you can also use that article as a jumping-off point for more research.

Climate Change Solutions

Renewable energy: Scientists agree that to avoid the most catastrophic effects of climate change, countries must immediately move away from dirty energy sources like coal, oil and gas, and instead turn to renewable energy sources like wind, solar or nuclear power. Read about the potent possibilities of one of these producers, offshore wind farms , and see how they operate .

Refrigerants: It’s not the most exciting solution to climate change, but it is one of the most effective. Read about how making refrigerants, like air-conditioners, more efficient could eliminate a full degree Celsius of warming by 2100.

Transportation: Across the globe, governments are focused on limiting one of the world’s biggest sources of pollution: gasoline-powered cars. Read about the promises and challenges of electric vehicles or about how countries are rethinking their transit systems .

Methane emissions: You hear a lot about the need to reduce carbon dioxide in the atmosphere, but what about its dangerous cousin, methane? Read about ideas to halt methane emissions and why doing so could be powerful in the short-term fight against climate change.

Agriculture: Efforts to limit global warming often target fossil fuels, but cutting greenhouse gases from food production is urgent, too, research says. Read about four fixes to earth’s food supply that could go a long way.

Nature conservation: Scientists agree that reversing biodiversity loss is a crucial way to slow climate change. Read about how protecting and restoring nature can help cool the planet or about how Indigenous communities could lead the way .

Carbon capture: Eliminating emissions alone may not be enough to avoid some of the worst effects of climate change, so some companies are investing in technology that sucks carbon dioxide out of the air. Learn more about so-called engineered carbon removal .

Questions to Consider

As you read about your climate solution, respond to the questions below. You can record your answers in this graphic organizer (PDF).

1. What is the solution? How does it work?

2. What problem related to climate change does this strategy address?

3. What effect could it have on global warming?

4. Compared with other ways to mitigate climate change, how effective is this one? Why?

5. What are the limitations of this solution?

6. What are some of the challenges or risks (political, social, economic or technical) of this idea?

7. What further questions do you have about this strategy?

When you’ve finished, you’ll meet in “teaching groups” with at least one expert in each of the other climate solutions. Share what you know about your topic with your classmates and record what you learn from them in your graphic organizer .

Going Further

Option 1: Develop a climate plan.

Scientists say that in order to prevent the average global temperature from rising more than 1.5 degrees Celsius, the threshold beyond which the dangers of global warming grow immensely, we will need to enact all of the solutions you learned about — and more. However, the reality is that countries won’t be able to right away. They will have to consider which can have the biggest or fastest impact on climate change, which are the most cost-effective and which are the most politically and socially feasible.

Imagine you have been asked to come up with a plan to address climate change. If you were in charge, which of these seven solutions would you prioritize and why? You might start by ranking the solutions you learned about from the most effective or urgent to the least.

Then, write a proposal for your plan that responds to the following questions:

What top three solutions are priorities? That is, which do you think are the most urgent to tackle right away and the most effective at slowing global warming?

Explain your decisions. According to your research — the articles you read and the quiz you took in the beginning of the lesson — why should these solutions take precedence?

How might you incentivize companies and citizens to embrace these changes? For some ideas, you might read more about the climate policies countries around the world have adopted to help reduce greenhouse gas emissions.

Option 2: Take action.

Thinking about climate change solutions on such a big scale can be overwhelming, but there are things you can do in your own life and in your community to make a difference. Choose one of the activities below to take action on, or come up with one of your own:

Share climate solutions via media. Often, the news media focuses more on climate change problems than solutions. Counteract this narrative by creating something for publication related to one or more of the solutions you learned about. For example, you could submit a letter to the editor , write an article for your school newspaper, enter a piece in one of our upcoming student contests or create an infographic to share on social media .

Make changes in your own life. How can you make good climate choices related to one or more of the topics you learned about? For example, you could eat less meat, take public transportation or turn off your air-conditioner. Write a plan, explaining what you will do (or what you are already doing) and how it could help mitigate climate change, according to the research.

Join a movement. This guest essay urges people to focus on systems, not themselves. What groups could you get involved with that are working toward some of the solutions you learned about? Identify at least one group, either local, national or international, and one way you could support it. Or, if you’re old enough to vote, consider a local, state or federal politician you would like to support based on his or her climate policies.

Want more Lessons of the Day? You can find them all here .

Natalie Proulx joined The Learning Network as a staff editor in 2017 after working as an English language arts teacher and curriculum writer. More about Natalie Proulx

Climate Change Essay for Students and Children


500+ Words Climate Change Essay

Climate change refers to the change in the environmental conditions of the earth. This happens due to many internal and external factors. The climatic change has become a global concern over the last few decades. Besides, these climatic changes affect life on the earth in various ways. These climatic changes are having various impacts on the ecosystem and ecology. Due to these changes, a number of species of plants and animals have gone extinct.

academic essay on climate change

When Did it Start?

The climate started changing a long time ago due to human activities but we came to know about it in the last century. During the last century, we started noticing the climatic change and its effect on human life. We started researching on climate change and came to know that the earth temperature is rising due to a phenomenon called the greenhouse effect. The warming up of earth surface causes many ozone depletion, affect our agriculture , water supply, transportation, and several other problems.

Reason Of Climate Change

Although there are hundreds of reason for the climatic change we are only going to discuss the natural and manmade (human) reasons.

Get the huge list of more than 500 Essay Topics and Ideas

Natural Reasons

These include volcanic eruption , solar radiation, tectonic plate movement, orbital variations. Due to these activities, the geographical condition of an area become quite harmful for life to survive. Also, these activities raise the temperature of the earth to a great extent causing an imbalance in nature.

Human Reasons

Man due to his need and greed has done many activities that not only harm the environment but himself too. Many plant and animal species go extinct due to human activity. Human activities that harm the climate include deforestation, using fossil fuel , industrial waste , a different type of pollution and many more. All these things damage the climate and ecosystem very badly. And many species of animals and birds got extinct or on a verge of extinction due to hunting.

Effects Of Climatic Change

These climatic changes have a negative impact on the environment. The ocean level is rising, glaciers are melting, CO2 in the air is increasing, forest and wildlife are declining, and water life is also getting disturbed due to climatic changes. Apart from that, it is calculated that if this change keeps on going then many species of plants and animals will get extinct. And there will be a heavy loss to the environment.

What will be Future?

If we do not do anything and things continue to go on like right now then a day in future will come when humans will become extinct from the surface of the earth. But instead of neglecting these problems we start acting on then we can save the earth and our future.

academic essay on climate change

Although humans mistake has caused great damage to the climate and ecosystem. But, it is not late to start again and try to undo what we have done until now to damage the environment. And if every human start contributing to the environment then we can be sure of our existence in the future.

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James E Hansen, Makiko Sato, Leon Simons, Larissa S Nazarenko, Isabelle Sangha, Pushker Kharecha, James C Zachos, Karina von Schuckmann, Norman G Loeb, Matthew B Osman, Qinjian Jin, George Tselioudis, Eunbi Jeong, Andrew Lacis, Reto Ruedy, Gary Russell, Junji Cao, Jing Li, Global warming in the pipeline, Oxford Open Climate Change , Volume 3, Issue 1, 2023, kgad008, https://doi.org/10.1093/oxfclm/kgad008

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Improved knowledge of glacial-to-interglacial global temperature change yields Charney (fast-feedback) equilibrium climate sensitivity 1.2 ± 0.3°C (2σ) per W/m 2 , which is 4.8°C ± 1.2°C for doubled CO 2 . Consistent analysis of temperature over the full Cenozoic era—including ‘slow’ feedbacks by ice sheets and trace gases—supports this sensitivity and implies that CO 2 was 300–350 ppm in the Pliocene and about 450 ppm at transition to a nearly ice-free planet, exposing unrealistic lethargy of ice sheet models. Equilibrium global warming for today’s GHG amount is 10°C, which is reduced to 8°C by today’s human-made aerosols. Equilibrium warming is not ‘committed’ warming; rapid phaseout of GHG emissions would prevent most equilibrium warming from occurring. However, decline of aerosol emissions since 2010 should increase the 1970–2010 global warming rate of 0.18°C per decade to a post-2010 rate of at least 0.27°C per decade. Thus, under the present geopolitical approach to GHG emissions, global warming will exceed 1.5°C in the 2020s and 2°C before 2050. Impacts on people and nature will accelerate as global warming increases hydrologic (weather) extremes. The enormity of consequences demands a return to Holocene-level global temperature. Required actions include: (1) a global increasing price on GHG emissions accompanied by development of abundant, affordable, dispatchable clean energy, (2) East-West cooperation in a way that accommodates developing world needs, and (3) intervention with Earth’s radiation imbalance to phase down today’s massive human-made ‘geo-transformation’ of Earth’s climate. Current political crises present an opportunity for reset, especially if young people can grasp their situation.

It has been known since the 1800s that infrared-absorbing (greenhouse) gases (GHGs) warm Earth’s surface and that the abundance of GHGs changes naturally as well as from human actions [ 1 , 2 ]. 1 Roger Revelle wrote in 1965 that we are conducting a ‘vast geophysical experiment’ by burning fossil fuels that accumulated in Earth’s crust over hundreds of millions of years [ 3 ] Carbon dioxide (CO 2 ) in the air is now increasing and already has reached levels that have not existed for millions of years, with consequences that have yet to be determined. Jule Charney led a study in 1979 by the United States National Academy of Sciences that concluded that doubling of atmospheric CO 2 was likely to cause global warming of 3 ± 1.5°C [ 4 ]. Charney added: ‘However, we believe it is quite possible that the capacity of the intermediate waters of the ocean to absorb heat could delay the estimated warming by several decades.’

After U.S. President Jimmy Carter signed the 1980 Energy Security Act, which included a focus on unconventional fossil fuels such as coal gasification and rock fracturing (‘fracking’) to extract shale oil and tight gas, the U.S. Congress asked the National Academy of Sciences again to assess potential climate effects. Their massive Changing Climate report had a measured tone on energy policy—amounting to a call for research [ 5 ]. Was not enough known to caution lawmakers against taxpayer subsidy of the most carbon-intensive fossil fuels? Perhaps the equanimity was due in part to a major error: the report assumed that the delay of global warming caused by the ocean’s thermal inertia is 15 years, independent of climate sensitivity. With that assumption, they concluded that climate sensitivity for 2 × CO 2 is near or below the low end of Charney’s 1.5–4.5°C range. If climate sensitivity was low and the lag between emissions and climate response was only 15 years, climate change would not be nearly the threat that it is.

Simultaneous with preparation of Changing Climate , climate sensitivity was addressed at the 1982 Ewing Symposium at the Lamont Doherty Geophysical Observatory of Columbia University on 25–27 October, with papers published in January 1984 as a monograph of the American Geophysical Union [ 6 ]. Paleoclimate data and global climate modeling together led to an inference that climate sensitivity is in the range 2.5–5°C for 2 × CO 2 and that climate response time to a forcing is of the order of a century, not 15 years [ 7 ]. Thus, the concept that a large amount of additional human-made warming is already ‘in the pipeline’ was introduced. E.E. David, Jr, President of Exxon Research and Engineering, in his keynote talk at the symposium insightfully noted [ 8 ]: ‘The critical problem is that the environmental impacts of the CO 2 buildup may be so long delayed. A look at the theory of feedback systems shows that where there is such a long delay, the system breaks down, unless there is anticipation built into the loop.’

Thus, the danger caused by climate’s delayed response and the need for anticipatory action to alter the course of fossil fuel development was apparent to scientists and the fossil fuel industry 40 years ago. 2 Yet industry chose to long deny the need to change energy course [ 9 ], and now, while governments and financial interests connive, most industry adopts a ‘greenwash’ approach that threatens to lock in perilous consequences for humanity. Scientists will share responsibility if we allow governments to rely on goals for future global GHG levels, as if targets had meaning in the absence of policies required to achieve them.

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 to provide scientific assessments on the state of knowledge about climate change [ 10 ] and almost all nations agreed to the 1992 United Nations Framework Convention on Climate Change [ 11 ] with the objective to avert ‘dangerous anthropogenic interference with the climate system’. The current IPCC Working Group 1 report [ 12 ] provides a best estimate of 3°C for equilibrium global climate sensitivity to 2 × CO 2 and describes shutdown of the overturning ocean circulations and large sea level rise on the century time scale as ‘high impact, low probability’ even under extreme GHG growth scenarios. This contrasts with ‘high impact, high probability’ assessments reached in a paper [ 13 ]—hereafter abbreviated Ice Melt—that several of us published in 2016. Recently, our paper’s first author (JEH) described a long-time effort to understand the effect of ocean mixing and aerosols on observed and projected climate change, which led to a conclusion that most climate models are unrealistically insensitive to freshwater injected by melting ice and that ice sheet models are unrealistically lethargic in the face of rapid, large climate change [ 14 ].

Eelco Rohling, editor of Oxford Open Climate Change, invited a perspective article on these issues. Our principal motivation in this paper is concern that IPCC has underestimated climate sensitivity and understated the threat of large sea level rise and shutdown of ocean overturning circulations, but these issues, because of their complexity, must be addressed in two steps. Our present paper addresses climate sensitivity and warming in the pipeline, concluding that these exceed IPCC’s best estimates. Response of ocean circulation and ice sheet dynamics to global warming—already outlined in the Ice Melt paper—will be addressed further in a later paper.

The structure of our present paper is as follows. Climate sensitivity section makes a fresh evaluation of Charney’s equilibrium climate sensitivity (ECS) based on improved paleoclimate data and introduces Earth system sensitivity (ESS), which includes the feedbacks that Charney held fixed. Climate response time section explores the fast-feedback response time of Earth’s temperature and energy imbalance to an imposed forcing, concluding that cloud feedbacks buffer heat uptake by the ocean, thus increasing the delay in surface warming and making Earth’s energy imbalance an underestimate of the forcing reduction required to stabilize climate. Cenozoic era section analyzes temperature change of the past 66 million years and infers the Cenozoic history of CO 2 , thus providing insights about climate change. Aerosols section addresses the absence of aerosol forcing data via inferences from paleo data and modern global temperature change, and we point out potential information in ‘the great inadvertent aerosol experiment’ provided by recent restrictions on fuels in international shipping. Summary section discusses policy implications of high climate sensitivity and the delayed response of the climate system. Warming in the pipeline need not appear. We can take actions that slow and reverse global warming; indeed, we suggest that such actions are needed to avoid disastrous consequences for humanity and nature. Reduction of greenhouse gas emissions as rapidly as practical has highest priority, but that policy alone is now inadequate and must be complemented by additional actions to affect Earth’s energy balance. The world is still early in this ‘vast geophysical experiment’—as far as consequences are concerned—but time has run short for the ‘anticipation’ that E.E. David recommended.

This section gives a brief overview of the history of ECS estimates since the Charney report and uses glacial-to-interglacial climate change to infer an improved estimate of ECS. We discuss how ECS and the more general Earth system sensitivity (ESS) depend on the climate state.

Charney defined ECS as the eventual global temperature change caused by doubled CO 2 if ice sheets, vegetation and long-lived GHGs are fixed (except the specified CO 2 doubling). Other quantities affecting Earth’s energy balance—clouds, aerosols, water vapor, snow cover and sea ice—change rapidly in response to climate change. Thus, Charney’s ECS is also called the ‘fast-feedback’ climate sensitivity. Feedbacks interact in many ways, so their changes are calculated in global climate models (GCMs) that simulate such interactions. Charney implicitly assumed that change of the ice sheets on Greenland and Antarctica—which we categorize as a ‘slow feedback’—was not important on time scales of most public interest.

ECS defined by Charney is a gedanken concept that helps us study the effect of human-made and natural climate forcings. If knowledge of ECS were based only on models, it would be difficult to narrow the range of estimated climate sensitivity—or have confidence in any range—because we do not know how well feedbacks are modeled or if the models include all significant real-world feedbacks. Cloud and aerosol interactions are complex, e.g. and even small cloud changes can have a large effect. Thus, data on Earth’s paleoclimate history are essential, allowing us to compare different climate states, knowing that all feedbacks operated.

Climate sensitivity estimated at the 1982 Ewing Symposium

We evaluated contributions of individual feedback processes to g by inserting changes of water vapor, clouds, and surface albedo (reflectivity, literally whiteness, due to sea ice and snow changes) from the 2 × CO 2 GCM simulation one-by-one into a one-dimensional radiative-convective model [ 16 ], finding g wv = 0.4, g cl = 0.2, g sa = 0.1, where g wv , g cl , and g sa are the water vapor, cloud and surface albedo gains. The 0.2 cloud gain was about equally from a small increase in cloud top height and a small decrease in cloud cover. These feedbacks all seemed reasonable, but how could we verify their magnitudes or the net ECS due to all feedbacks?

We recognized the potential of emerging paleoclimate data. Early data from polar ice cores revealed that atmospheric CO 2 was much less during glacial periods and the CLIMAP project [ 17 ] used proxy data to reconstruct global surface conditions during the Last Glacial Maximum (LGM), which peaked about 20 000 years ago. A powerful constraint was the fact that Earth had to be in energy balance averaged over the several millennia of the LGM. However, when we employed CLIMAP boundary conditions including sea surface temperatures (SSTs), Earth was out of energy balance, radiating 2.1 W/m 2 to space, i.e. Earth was trying to cool off with an enormous energy imbalance, equivalent to half of 2 × CO 2 forcing.

Something was wrong with either assumed LGM conditions or our climate model. We tried CLIMAP’s maximal land ice—this only reduced the energy imbalance from 2.1 to 1.6 W/m 2 . Moreover, we had taken LGM CO 2 as 200 ppm and did not know that CH 4 and N 2 O were less in the LGM than in the present interglacial period; accurate GHGs and CLIMAP SSTs produce a planetary energy imbalance close to 3 W/m 2 . Most feedbacks in our model were set by CLIMAP. Sea ice is set by CLIMAP. Water vapor depends on surface temperature, which is set by CLIMAP SSTs. Cloud feedback is uncertain, but ECS smaller than 2.4°C for 2 × CO 2 would require a negative cloud gain. g cl ∼ 0.2 from our GCM increases ECS from 2.4°C to 4°C ( Equation 1 ) and accounts for almost the entire difference of sensitivities of our model (4°C for 2 × CO 2 ) and the Manabe and Stouffer model [ 18 ] (2°C for 2 × CO 2 ) that had fixed cloud cover and cloud height. Manabe suggested [ 19 ] that our higher ECS was due to a too-large sea ice and snow feedback, but we noted [ 7 ] that sea ice in our control run was less than observed, so we likely understated sea ice feedback. Amplifying feedback due to high clouds increasing in height with warming is expected and is found in observations, large-eddy simulations and GCMs [ 20 ] Sherwood et al . [ 21 ] conclude that negative low-cloud feedback is ‘neither credibly suggested by any model, nor by physical principles, nor by observations.’ Despite a wide spread among models, GCMs today show an amplifying cloud feedback due to increases in cloud height and decreases in cloud amount, despite increases in cloud albedo [ 22 ]. These cloud changes are found in all observed cloud regimes and locations, implying robust thermodynamic control [ 23 ].

CLIMAP SSTs were a more likely cause of the planetary energy imbalance. Co-author D. Peteet used pollen data to infer LGM tropical and subtropical cooling 2–3°C greater than in a GCM forced by CLIMAP SSTs. D. Rind and Peteet found that montane LGM snowlines in the tropics descended 1 km in the LGM, inconsistent with climate constrained by CLIMAP SSTs. CLIMAP assumed that tiny shelled marine species migrate to stay in a temperature zone they inhabit today. But what if, instead, these species partly adapt over millennia to changing temperature? Based on the work of Rind and Peteet, later published [ 24 ], we suspected but could not prove that CLIMAP SSTs were too warm.

Based on GCM simulations for 2 × CO 2 , on our feedback analysis for the LGM, and on observed global warming in the past century, we concluded that ECS was in the range 2.5–5°C for 2 × CO 2 . If CLIMAP SSTs were accurate, ECS was near the low end of that range. In contrast, our analysis implied that ECS for 2 × CO 2 was in the upper half of the 2.5–5°C range, but our analysis depended in part on our GCM, which had sensitivity 4°C for 2 × CO 2 . To resolve the matter, a paleo thermometer independent of biologic adaptation was needed. Several decades later, such a paleo thermometer and advanced analysis techniques exist. We will use recent studies to infer our present best estimates for ECS and ESS. First, however, we will comment on other estimates of climate sensitivity and clarify the definition of climate forcings that we employ.

IPCC and independent climate sensitivity estimates

Reviews of climate sensitivity are available, e.g. Rohling et al . [ 25 ], which focuses on the physics of the climate system, and Sherwood et al . [ 26 ], which adds emphasis on probabilistic combination of multiple uncertainties. Progress in narrowing the uncertainty in climate sensitivity was slow in the first five IPCC assessment reports. The fifth assessment report [ 26 ] (AR5) in 2014 concluded only—with 66% probability—that ECS was in the range 1.5–4.5°C, the same as Charney’s report 35 years earlier. The broad spectrum of information on climate change—especially constraints imposed by paleoclimate data—at last affected AR6 [ 12 ], which concluded with 66% probability that ECS is 2.5–4°C, with 3°C as their best estimate ( Supplementary Fig. TS.6 ).

Sherwood et al . [ 21 ] combine three lines of evidence: climate feedback studies, historical climate change, and paleoclimate data, inferring S = 2.6–3.9°C with 66% probability for 2 × CO 2 , where S is an ‘effective sensitivity’ relevant to a 150-year time scale. They find ECS only slightly larger: 2.6–4.1°C with 66% probability. Climate feedback studies, inherently, cannot yield a sharp definition of ECS, as we showed in the cloud feedback discussion above. Earth’s climate system includes amplifying feedbacks that push the gain, g, closer to unity than zero, thus making ECS sensitive to uncertainty in any feedback; the resulting sensitivity of ECS to g prohibits precise evaluation from feedback analysis. Similarly, historical climate change cannot define ECS well because the aerosol climate forcing is unmeasured. Also, forced and unforced ocean dynamics give rise to a pattern effect: [ 27 ] the geographic pattern of transient and equilibrium temperature changes differ, which affects ECS inferred from transient climate change. These difficulties help explain how Sherwood et al . [ 21 ] could estimate ECS as only 6% larger than S , an implausible result in view of the ocean’s great thermal inertia. An intercomparison of GCMs run for millennial time scales, LongRunMIP [ 28 ], includes 14 simulations of 9 GCMs with runs of 5000 years (or close enough for extrapolation to 5000 years). Their global warmings at 5000 years range from 30% to 80% larger than their 150-year responses.

Our approach is to compare glacial and interglacial equilibrium climate states. The change of atmospheric and surface forcings can be defined accurately, thus leading to a sharp evaluation of ECS for cases in which equilibrium response is assured. With this knowledge in hand, additional information can be extracted from historical and paleo climate changes.

Climate forcing definitions

Attention to climate forcing definitions is essential for quantitative analysis of climate change. However, readers uninterested in radiative forcings may skip this section with little penalty. We describe our climate forcing definition and compare our forcings with those of IPCC. Our total GHG forcing matches that of IPCC within a few percent, but this close fit hides larger differences in individual forcings that deserve attention.

A further refinement of climate forcing is suggested in Efficacy : effective forcing (F e ) defined by a long GCM run with calculated ocean temperature. The resulting global surface temperature change, relative to that for equal CO 2 forcing, defines the forcing’s efficacy. Effective forcings, F e , were found to be within a few percent of F s for most forcing agents, i.e. the results confirm that F s is a robust forcing. This support is for F s , not for F o = ERF, which is systematically smaller than F s . The Goddard Institute for Space Studies (GISS) GCM [ 32 , 33 ] used for CMIP6 [ 34 ] studies, which we label the GISS (2020) model, 3 has higher resolution (2° × 2.5° and 40 atmospheric layers) and other changes that yield a moister upper troposphere and lower stratosphere, relative to the GISS model used in Efficacy . GHG forcings reported for the GISS (2020) model [ 32 , 33 ] are smaller than in prior GISS models, a change attributed [ 33 ] to blanketing by high level water vapor. However, part of the change is from comparison of F o in GISS (2020) to F S in earlier models. The 2 × CO 2 fixed SST simulation with the GISS (2020) model yields F o = 3.59 W/m 2 , δTo = 0.27°C and λ = 0.9°C per W/m 2 . Thus F S = 3.59 + 0.30 = 3.89 W/m 2 , which is only 5.4% smaller than the F S = 4.11 W/m 2 for the GISS model used in Efficacy .

Greenhouse gas radiative forcings

c, CO 2 (ppm); m, CH 4 (ppb); n, N 2 O (ppb); x/y, CFC-11/12 (ppb).

The CH 4 coefficient (1.45) includes the effect of CH 4 on O 3 and stratospheric H 2 O, as well as the efficacy (1.10) of CH 4 per se . We assume that CH 4 is responsible for 45% of the O 3 change [ 37 ]. Forcing caused by the remaining 55% of the O 3 change is based on IPCC AR6 O 3 forcing (Fa = 0.47 W/m 2 in 2019); we multiply this AR6 O 3 forcing by 0.55 × 0.82 = 0.45, where 0.82 is the efficacy of O 3 forcing from Table 1 of Efficacy . Thus, the non-CH 4 portion of the O 3 forcing is 0.21 W/m 2 in 2019. MPTGs and OTGs are Montreal Protocol Trace Gases and Other Trace Gases [ 38 ]. A list of these gases and a table of annual forcings since 1992 are available as well as the earlier data [ 39 ].

The climate forcing from our formulae is slightly larger than IPCC AR6 forcings ( Fig. 1 ). In 2019, the final year of AR6 data, our GHG forcing is 4.00 W/m 2 ; the AR6 forcing is 3.84 W/m 2 . Our forcing should be larger, because IPCC forcings are F o for all gases except O 3 , for which they provide F a (AR6 section Table 1 in Efficacy allows accurate comparison: δT o for 2 × CO 2 for the GISS model used in Efficacy is 0.22°C, λ is 0.67°C per W/m 2 , so δT o /λ = 0.33 W/m 2 . Thus, the conversion factor from F o to F e (or F s ) is 4.11/(4.11−0.33). The non-O 3 portion of AR6 2019 forcing (3.84−0.47 = 3.37) W/m 2 increases to 3.664 W/m 2 . The O 3 portion of the AR6 2019 forcing (0.47 W/m 2 ) decreases to 0.385 W/m 2 because the efficacy of F a (O 3 ) is 0.82. The AR6 GHG forcing in 2019 is thus ∼4.05 W/m 2 , expressed as Fe ∼ Fs, which is ∼1% larger than follows from our formulae. This precise agreement is not indicative of the true uncertainty in the GHG forcing, which IPCC AR6 estimates as 10%, thus about 0.4 W/m 2 . We concur with their error estimate and employ it in our ECS uncertainty analysis (Equilibrium climate sensitivity section).

IPCC AR6 Annex III greenhouse gas forcing [12], which employs Fa for O3 and Fo for other GHGs, compared with the effective forcing, Fe, from Equation (4). See discussion in text.

IPCC AR6 Annex III greenhouse gas forcing [ 12 ], which employs F a for O 3 and F o for other GHGs, compared with the effective forcing, F e , from Equation (4) . See discussion in text.

We conclude that the GHG increase since 1750 already produces a climate forcing equivalent to that of 2 × CO 2 (our formulae yield F e ∼ F s = 4.08 W/m 2 for 2021 and 4.13 W/m 2 for 2022; IPCC AR6 has F s = 4.14 W/m 2 for 2021). The human-made 2 × CO 2 climate forcing imagined by Charney, Tyndall and other greenhouse giants is no longer imaginary. Humanity is now taking its first steps into the period of consequences. Earth’s paleoclimate history helps us assess the potential outcomes.

Glacial-to-interglacial climate oscillations

In this section we describe how ice core data help us assess ECS for climate states from glacial conditions to interglacial periods such as the Holocene, the interglacial period of the past 12 000 years. We discuss climate sensitivity in warmer climates in Cenozoic era section.

Air bubbles in Antarctic ice cores—trapped as snow piled up and compressed into ice—preserve a record of long-lived GHGs for at least 800 000 years. Isotopic composition of the ice provides a measure of temperature in and near Antarctica [ 40 ]. Changes of temperature and CO 2 are highly correlated ( Fig. 2 ). This does not mean that CO 2 is the primal cause of the climate oscillations. Hays et al . [ 42 ] showed that small changes of Earth’s orbit and the tilt of Earth’s spin axis are pacemakers of the ice ages. Orbital changes alter the seasonal and geographical distribution of insolation, which affects ice sheet size and GHG amount. Long-term climate is sensitive because ice sheets and GHGs act as amplifying feedbacks: [ 43 ] as Earth warms, ice sheets shrink, expose a darker surface, and absorb more sunlight; also, as Earth warms, the ocean and continents release GHGs to the air. These amplifying feedbacks work in the opposite sense as Earth cools. Orbital forcings oscillate slowly over tens and hundreds of thousands of years [ 44 ]. The picture of how Earth orbital changes drive millennial climate change was painted in the 1920s by Milutin Milankovitch, who built on 19th century hypotheses of James Croll and Joseph Adhémar. Paleoclimate changes of ice sheets and GHGs are sometimes described as slow feedbacks [ 45 ], but their slow change is paced by the Earth orbital forcing; their slow change does not mean that these feedbacks cannot operate more rapidly in response to a rapid climate forcing.

Antarctic Dome C temperature for past 800 ky from Jouzel et al. [40] relative to the mean of the last 10 ky and Dome C CO2 amount from Luthi et al. [41] (kyBP is kiloyears before present).

Antarctic Dome C temperature for past 800 ky from Jouzel et al . [ 40 ] relative to the mean of the last 10 ky and Dome C CO 2 amount from Luthi et al . [ 41 ] (kyBP is kiloyears before present).

We evaluate ECS by comparing stable climate states before and after a glacial-to-interglacial climate transition. GHG amounts are known from ice cores and ice sheet sizes are known from geologic data. This empirical ECS applies to the range of global temperature covered by ice cores, which we will conclude is about –7°C to + 1°C relative to the Holocene. The Holocene is an unusual interglacial. Maximum melt rate was at 13.2 kyBP, as expected [ 45 ] and GHG amounts began to decline after peaking early in the Holocene, as in most interglacials. However, several ky later, CO 2 and CH 4 increased, raising a question of whether humans were affecting GHGs. Ruddiman [ 46 ] suggests that deforestation began to affect CO 2 6500 years ago and rice irrigation began to affect CH 4 5000 years ago. Those possibilities complicate use of LGM-Holocene warming to estimate ECS. However, sea level, and thus the size of the ice sheets, had stabilized by 7000 years ago (Evidence of aerosol forcing in the Holocene section). Thus, the millennium centered on 7 kyBP provides a good period to compare with the LGM. Comparison of the Eemian interglacial ( Fig. 2 ) with the prior glacial maximum (PGM) has potential for independent assessment.

LGM-Holocene and PGM-Eemian evaluation of ECS

In this section we evaluate ECS by comparing neighboring glacial and interglacial periods when Earth was in energy balance within less than 0.1 W/m 2 averaged over a millennium. Larger imbalance would cause temperature or sea level change that did not occur [ 48 ]. 4 Thus, we can assess ECS from knowledge of atmospheric and surface forcings that maintained these climates.

Recent advanced analysis techniques allow improved estimate of paleo temperatures. Tierney et al . [ 49 ] exclude microbiology fossils whose potential to adapt makes them dubious thermometers. Instead, they use a large collection of geochemical (isotope) proxies for SST in an analysis constrained by climate change patterns defined by GCMs. They find cooling of 6.1°C (95% confidence: 5.7–6.5°C) for the interval 23–19 kyBP. A similarly constrained global analysis by Osman et al . [ 50 ] finds LGM cooling at 21–18 kyBP of 7.0 ± 1°C (95% confidence). Tierney (priv. comm.) attributes the difference between the two studies to the broader time interval of the former study, and concludes that peak LGM cooling was near 7°C.

Seltzer et al . [ 51 ] use the temperature-dependent solubility of dissolved noble gases in ancient groundwater to show that land areas between 45°S and 35°N cooled 5.8 ± 0.6°C in the LGM. This cooling is consistent with 1 km lowering of alpine snowlines found by Rind and Peteet [ 24 ]. Land response to a forcing exceeds ocean response, but polar amplification makes the global response as large as the low latitude land response in GCM simulations with fixed ice sheets ( Supplementary Material Fig. S3 ). When ice sheet growth is added, cooling amplification at mid and high latitudes is greater [ 7 ], making 5.8°C cooling of low latitude land consistent with global cooling of ∼7°C.

LGM CO 2 , CH 4 and N 2 O amounts are known accurately with the exception of N 2 O in the PGM when N 2 O reactions with dust in the ice core corrupt the data. We take PGM N 2 O as the mean of the smallest reported PGM amount and the LGM amount; potential error in the N 2 O forcing is ∼0.01 W/m 2 . We calculate CO 2 , CH 4 , and N 2 O forcings using Equation (4) and formulae for each gas in Supplementary Material for the periods shown by green bars in Fig. 3 . The Eemian period avoids early CO 2 and temperature spikes, assuring that Earth was in energy balance. Between the LGM (19–21 kyBP) and Holocene (6.5–7.5 kyBP), GHG forcing increased 2.25 W/m 2 with 77% from CO 2 . Between the PGM and Eemian, GHG forcing increased 2.30 W/m 2 with 79% from CO 2 .

Dome C temperature (Jouzel et al. [40]) and multi-ice core GHG amounts (Schilt et al. [47]). Green bars (1–5, 6.5–7.5, 18–21, 120–126, 137–144 kyBP) are periods of calculations.

Dome C temperature (Jouzel et al . [ 40 ]) and multi-ice core GHG amounts (Schilt et al . [ 47 ]). Green bars (1–5, 6.5–7.5, 18–21, 120–126, 137–144 kyBP) are periods of calculations.

Glacial-interglacial aerosol changes are not included as a forcing. Natural aerosol changes, like clouds, are fast feedbacks. Indeed, aerosols and clouds form a continuum and distinction is arbitrary as humidity approaches 100%. There are many aerosol types, including VOCs (volatile organic compounds) produced by trees, sea salt produced by wind and waves, black and organic carbon produced by forest and grass fires, dust produced by wind and drought, and marine biologic dimethyl sulfide and its secondary aerosol products, all varying geographically and in response to climate change. We do not know, or need to know, natural aerosol properties in prior eras because their changes are feedbacks included in the climate response. However, human-made aerosols are a climate forcing (an imposed perturbation of Earth’s energy balance). Humans may have begun to affect gases and aerosols in the latter Holocene (Aerosols section), but we minimize that issue by using the 6.5–7.5 kyBP window to evaluate climate sensitivity.

Earth’s surface change is the other forcing needed to evaluate ECS: (1) change of surface albedo (reflectivity) and topography by ice sheets, (2) vegetation change, e.g. boreal forests replaced by brighter tundra, and (3) continental shelves exposed by lower sea level. Forcing by all three can be evaluated at once with a GCM. Accuracy requires realistic clouds, which shield the surface. Clouds are the most uncertain feedback [ 52 ]. Evaluation is ideal for CMIP [ 53 ] (Coupled Model Intercomparison Project) collaboration with PMIP [ 54 ] (Paleoclimate Modelling Intercomparison Project); a study of LGM surface forcing could aid GCM development and assessment of climate sensitivity. Sherwood et al . [ 21 ] review studies of LGM ice sheet forcing and settle on 3.2 ± 0.7 W/m 2 , the same as IPCC AR4 [ 55 ]. However, some GCMs yield efficacies as low as ∼0.75 [ 56 ] or even ∼0.5 [ 57 ], likely due to cloud shielding. We found [ 7 ] a forcing of −0.9 W/m 2 for LGM vegetation by using the Koppen [ 58 ] scheme to relate vegetation to local climate, but we thought the model effect was exaggerated as real-world forests tends to shake off snow albedo effects. Kohler et al . [ 59 ] estimate a continental shelf forcing of −0.67 W/m 2 . Based on an earlier study [ 60 ] (hereafter Target CO 2 ), our estimate of LGM-Holocene surface forcing is 3.5 ± 1 W/m 2 . Thus, LGM (18–21 kyBP) cooling of 7°C relative to mid-Holocene (7 kyBP), GHG forcing of 2.25 W/m 2 , and surface forcing of 3.5 W/m 2 yield an initial ECS estimate 7/(2.25 + 3.5) = 1.22°C per W/m 2 . We discuss uncertainties in Equilibrium climate sensitivity section.

PGM-Eemian global warming provides a second assessment of ECS, one that avoids concern about human influence. PGM-Eemian GHG forcing is 2.3 W/m 2 . We estimate surface albedo forcing as 0.3 W/m 2 less than in the LGM because sea level was about 10 m higher during the PGM [ 61 ]. North American and Eurasian ice sheet sizes differed between the LGM and PGM [ 62 ], but division of mass between them has little effect on the net forcing ( Supplementary Fig. S4 [ 60 ]). Thus, our central estimate of PGM-Eemian forcing is 5.5 W/m 2 . Eemian temperature reached about +1°C warmer than the Holocene [ 63 ], based on Eemian SSTs of +0.5 ± 0.3°C relative to 1870–1889 [ 64 ], or +0.65 ± 0.3°C SST and +1°C global (land plus ocean) relative to 1880–1920. However, the PGM was probably warmer than the LGM; it was warmer at Dome C ( Fig. 2 ), but cooler at Dronning Maud Land [ 65 ]. Based on deep ocean temperatures (Cenozoic Era section), we estimate PGM-Eemian warming as 0.5°C greater than LGM-Holocene warming, that is 7.5°C. The resulting ECS is 7.5/5.5 = 1.36°C per W/m 2 . Although PGM temperature lacks quantification comparable to that of Seltzer et al . [ 51 ] and Tierney et al . [ 49 ] for the LGM, the PGM-Eemian warming provides support for the high ECS inferred from LGM-Holocene warming.

We conclude that ECS for climate in the Holocene-LGM range is 1.2°C ± 0.3°C per W/m 2 , where the uncertainty is the 95% confidence range. The uncertainty estimate is inherently subjective, as it depends mainly on the ice age surface albedo forcing. The GHG forcing and glacial-interglacial temperature change are well-defined, but the efficacy of ice age surface forcing varies among GCMs. This variability is likely related to cloud shielding of surface albedo, which reaffirms the need for a focus on precise cloud observations and modeling.

State dependence of climate sensitivity

ECS based on glacial-interglacial climate is an average for global temperatures −7°C to +1°C relative to the Holocene and in general differs for other climate states because water vapor, aerosol-cloud and sea ice feedbacks depend on the initial climate. However, ECS is rather flat between today’s climate and warmer climate, based on a study [ 66 ] covering a range of 15 CO 2 doublings using an efficient GCM developed by Gary Russell [ 67 ]. Toward colder climate, ice-snow albedo feedback increases nonlinearly, reaching snowball Earth conditions—with snow and ice on land reaching sea level in the tropics—when CO 2 declines to a quarter to an eighth of its 1950 abundance ( Fig. 7 of the study) [ 66 ]. Snowball Earth occurred several times in Earth’s history, most recently about 600 million years ago [ 68 ] when the Sun was 6% dimmer [ 69 ] than today, a forcing of about –12 W/m 2 . Toward warmer climate, the water vapor feedback increases as the tropopause rises [ 70 ], the tropopause cold trap disappearing at 32 × CO 2 ( Fig. 7 ) [ 66 ]. However, for the range of ECS of practical interest—say from half preindustrial CO 2 to 4 × CO 2 —state dependence of ECS is small compared to state dependence of ESS.

Earth system sensitivity (ESS) includes amplifying feedbacks of GHGs and ice sheets [ 71 ]. When we consider CO 2 change as a known forcing, other GHGs provide a feedback that is smaller than the ice sheet feedback, but not negligible. Ice core data on GHG amounts show that non-CO 2 GHGs—including O 3 and stratospheric H 2 O produced by changing CH 4 —provide about 20% of the total GHG forcing, not only on average for the full glacial-interglacial change, but as a function of global temperature right up to +1°C global temperature relative to the Holocene ( Supplementary Fig. S5 ). Atmospheric chemistry modeling suggests that non-CO 2 GHG amplification of CO 2 forcing by about a quarter continues into warmer climate states [ 72 ]. Thus, for climate change in the Cenozoic era, we approximate non-CO 2 GHG forcing by increasing the CO 2 forcing by one-quarter.

Ice sheet feedback, in contrast to non-CO 2 GHG feedback, is highly nonlinear. Preindustrial climate was at most a few halvings of CO 2 from runaway snowball Earth and LGM climate was even closer to that climate state. The ice sheet feedback is reduced as Earth heads toward warmer climate today because already two-thirds of LGM ice has been lost. Yet remaining ice on Antarctica and Greenland constitutes a powerful feedback, which humanity is about to bring into play. We can illuminate that feedback and the climate path Earth is now on by examining data on the Cenozoic era—which includes CO 2 levels comparable to today’s amount—but first we must consider climate response time.

In this section we define response functions for global temperature and Earth’s energy imbalance that help reveal the physics of climate change. Cloud feedbacks amplify climate sensitivity and thus increase eventual heat uptake by the ocean, but cloud feedbacks also have the potential to buffer the rate at which the ocean takes up heat, thus increasing climate response time.

Climate response time was surprisingly long in our climate simulations [ 7 ] for the 1982 Ewing Symposium. The e-folding time—the time for surface temperature to reach 63% of its equilibrium response—was about a century. The only published atmosphere-ocean GCM—that of Bryan and Manabe [ 73 ]—had a response time of 25 years, while several simplified climate models referenced in our Ewing paper had even faster responses. The longer response time of our climate model was largely a result of high climate sensitivity—our model had an ECS of 4°C for 2 × CO 2 while the Bryan and Manabe model had an ECS of 2°C.

The physics is straightforward. If the delay were a result of a fixed source of thermal inertia, say the ocean’s well-mixed upper layer, response time would increase linearly with ECS because most climate feedbacks come into play in response to temperature change driven by the adjusted forcing, not in direct response to the forcing. Thus, a model with ECS of 4°C takes twice as long to reach full response as a model with ECS of 2°C, if the mixed layer provides the only heat capacity. However, while the mixed layer is warming, there is exchange of water with the deeper ocean, which slows the mixed layer warming. The longer response time with high ECS allows more of the ocean to come into play. If mixing into the deeper ocean is approximated as diffusive, surface temperature response time is proportional to the square of climate sensitivity [ 74 ].

Slow climate response accentuates need for the ‘anticipation’ that E.E. David, Jr spoke about. If ECS is 4.8°C (1.2°C per W/m 2 ), more warming is in the pipeline than widely assumed. GHG forcing today already exceeds 4 W/m 2 . Aerosols reduce the net forcing to about 3 W/m 2 , based on IPCC estimates (Aerosols section), but warming still in the pipeline for 3 W/m 2 forcing is 2.4°C, exceeding warming realized to date (1.2°C). Slow feedbacks increase the equilibrium response even further (Summary section). Large warmings can be avoided via a reasoned policy response, but definition of effective policies will be aided by an understanding of climate response time.

Temperature response function

T G is the Green’s function estimate of global temperature at time t, λ (°C per W/m 2 ) the model’s equilibrium sensitivity, R the dimensionless temperature response function (% of equilibrium response), and dF e the forcing change per unit time, dt. Integration over time begins when Earth is in near energy balance, e.g. in preindustrial time. The response function yields an accurate estimate of global temperature change for a forcing that does not cause reorganization of ocean circulation. Accuracy of this approximation for temperature for one climate model is shown in Chart 15 in the Bjerknes presentation and wider applicability has been demonstrated [ 76 ].

We study ocean mixing effects by comparing two GCMs: GISS (2014) [ 77 ] and GISS (2020) [ 33 ], both models 6 described by Kelley et al . [ 32 ].Ocean mixing is improved in GISS (2020) by use of a high-order advection scheme [ 78 ], finer upper-ocean vertical resolution (40 layers), updated mesoscale eddy parameterization, and correction of errors in the ocean modeling code [ 32 ]. The GISS (2020) model has improved variability, including the Madden-Julian Oscillation (MJO), El Nino Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), but the spectrum of ENSO-like variability is unrealistic and its amplitude is excessive, as shown by the magnitude of oscillations in Fig. 4a . Ocean mixing in GISS (2020) may still be excessive in the North Atlantic, where the model’s simulated penetration of CFCs is greater than observed [ 79 ].

(a) Global mean surface temperature response to instant CO2 doubling and (b) normalized response function (percent of final change). Thick lines in Figs 4 and 5 are smoothed (yr1 no smoothing; yr2 3-yr mean; yr3–12 5-yr mean, yr13–300 25-yr mean; yr301–5000 101-yr mean).

( a ) Global mean surface temperature response to instant CO 2 doubling and ( b ) normalized response function (percent of final change). Thick lines in Figs 4 and 5 are smoothed (yr1 no smoothing; yr2 3-yr mean; yr3–12 5-yr mean, yr13–300 25-yr mean; yr301–5000 101-yr mean).

Despite reduced ocean mixing, the GISS (2020) model surface temperature response is no faster than in the GISS (2014) model ( Fig. 4b ): it takes 100 years to reach within 1/e of the equilibrium response. Slow response is partly explained by the larger ECS of the GISS (2020) model, which is 3.5°C versus 2.7°C for the GISS (2014) model, but something more is going on in the newer model, as exposed by the response function of Earth’s energy imbalance.

Earth’s energy imbalance (EEI)

When a forcing perturbs Earth’s energy balance, the imbalance drives warming or cooling to restore balance. Observed EEI is now of order +1 W/m 2 (more energy coming in than going out) [ 80 ]. High accuracy of EEI is obtained by tracking ocean warming—the main repository for excess energy—and adding heat stored in warming continents and heat used in net ice melt [ 80 ]. Heat storage in air adds a small amount. Radiation balance measured from Earth-orbiting satellites cannot by itself define the absolute imbalance, but, when anchored to an in situ EEI value for a sufficient interval (e.g. 10 years), satellite Earth radiation budget observations [ 81 ] provide invaluable EEI data on finer temporal and spatial scales than the in situ data.

After a step-function forcing is imposed, EEI and global surface temperature must each approach a new equilibrium, but EEI does so more rapidly, especially for the GISS (2020) model ( Fig. 5 ). EEI in GISS (2020) needs only a decade to reach within 1/e of full response ( Fig. 5b ), but global surface temperature requires a century ( Fig. 4b ). Rapid decline of EEI—to half the forcing in 5 years ( Fig. 5a )—has practical implications. First, EEI defines the rate heat is pumped into the ocean, so if EEI is reduced, ocean warming is slowed. Second, rapid EEI decline implies that it is wrong to assume that global warming can be stopped by a reduction of climate forcing by the amount of EEI. Instead, the required reduction of forcing is larger than EEI. The difficulty in finding additional reduction in climate forcing of even a few tenths of a W/m 2 is substantial [ 63 ]. Calculations that help quantify this matter are discussed in Supplementary Material section SM8 .

(a) Earth’s energy imbalance (EEI) for 2 × CO2, and (b) EEI normalized response function.

( a ) Earth’s energy imbalance (EEI) for 2 × CO 2 , and ( b ) EEI normalized response function.

What is the physics behind the fast response of EEI? The 2 × CO 2 forcing and initial EEI are both nominally 4 W/m 2 . In the GISS (2014) model, the decline of EEI averaged over the first year is 0.5 W/m 2 ( Fig. 5a ), a moderate decline that might be largely caused by warming continents and thus increased heat radiation to space. In contrast, EEI declines 1.3 W/m 2 in the GISS (2020) model ( Fig. 5a ). Such a huge, immediate decline of EEI implies existence of an ultrafast climate feedback. Climate feedbacks are the heart of climate change and warrant discussion.

Slow, fast and ultrafast feedbacks

Charney et al . [ 4 ] described climate feedbacks without discussing time scales. At the 1982 Ewing Symposium, water vapor, clouds and sea ice were described as ‘fast’ feedbacks [ 7 ] presumed to change promptly in response to global temperature change, as opposed to ‘slow’ feedbacks or specified boundary conditions such as ice sheet size, vegetation cover, and atmospheric CO 2 amount, although it was noted that some specified boundary conditions, e.g. vegetation, in reality may be capable of relatively rapid change [ 7 ].

The immediate EEI response ( Fig. 5a ) implies a third feedback time scale: ultrafast. Ultrafast feedbacks are not a new concept. When CO 2 is doubled, the added infrared opacity causes the stratosphere to cool. Instant EEI upon CO 2 doubling is only F i = +2.5 W/m 2 , but stratospheric cooling quickly increases EEI to +4 W/m 2 [ 82 ]. All models calculate a similar radiative effect, so it is useful to define an adjusted forcing, F a , which is superior to F i as a measure of climate forcing. In contrast, if cloud change—the likely cause of the present ultrafast change—is lumped into the adjusted forcing, each climate model has its own forcing, losing the merit of a common forcing.

Kamae et al . [ 83 ] review rapid cloud adjustment distinct from surface temperature-mediated change. Clouds respond to radiative forcing, e.g. via effects on cloud particle phase, cloud cover, cloud albedo and precipitation [ 84 ]. The GISS (2020) model alters glaciation in stratiform mixed-phase clouds, which increases supercooled water in stratus clouds, especially over the Southern Ocean [ Fig. 1 in the GCM description [ 32 ]]. The portion of supercooled cloud water drops goes from too little in GISS (2014) to too much in GISS (2020). Neither model simulates well stratocumulus clouds, yet the models help expose real-world physics that affects climate sensitivity and climate response time. Several models in CMIP6 comparisons find high ECS [ 84 ]. For the sake of revealing the physics, it would be useful if the models defined their temperature and EEI response functions. Model runs of even a decade can define the important part of Figs 4a and 5a . Many short (e.g. 2-year) 2 × CO 2 climate simulations with each run beginning at a different point in the model’s control run, can define cloud changes to an arbitrary accuracy.

In this section, we use ocean sediment core data to explore climate change in the past 66 million years. This allows us to study warmer climates that are relevant to human-made climate forcing.

High equilibrium climate sensitivity that we have inferred, ECS = 1.2°C ± 0.3°C per W/m 2 , may affect interpretation of warmer climates. GCMs have difficulty in producing Pliocene warmth [ 85 ], especially in the Arctic, without large—probably unrealistic—CO 2 amounts. In addition, a coupled GCM/ice sheet model needs 700–840 ppm CO 2 for transition between glaciated and unglaciated Antarctica [ 86 ]. Understanding of these climate states is hampered by uncertainty in the forcings that maintained the climate, as proxy measures of CO 2 have large uncertainty.

Theory informs us that CO 2 is the principal control knob on global temperature [ 87 ]. Climate of the past 800 000 years demonstrates ( Fig. 2 ) the tight control. Our aim here is to extract Cenozoic surface temperature history from the deep ocean oxygen isotope δ 18 O and infer Cenozoic CO 2 history. Oxygen isotope data has high temporal resolution for the entire Cenozoic, which aids understanding of Cenozoic climate change and resulting implications for future climate. Our CO 2 analysis is a complement to proxy CO 2 measurements. Despite progress in estimating CO 2 via carbon isotopes in alkenones and boron isotopes in planktic foraminifera [ 88 ], there is wide scatter among results and fossil plant stomata suggest smaller CO 2 amounts [ 89 ].

Deep ocean temperature and sea level from δ 18 O

Global deep ocean δ18O. Black line: Westerhold et al. [90] data in 5 kyr bins until 34 MyBP and subsequently 2 kyr bins. Green line: Zachos et al. [44] data at 1 Myr resolution. Lower left: velocity [91] of Indian tectonic plate. PETM = Paleocene Eocene Thermal Maximum; EECO = Early Eocene Climatic Optimum; Oi-1 marks the transition to glaciated Antarctica; MCO = Miocene Climatic Optimum; NAIP = North Atlantic Igneous Province.

Global deep ocean δ 18 O. Black line: Westerhold et al . [ 90 ] data in 5 kyr bins until 34 MyBP and subsequently 2 kyr bins. Green line: Zachos et al . [ 44 ] data at 1 Myr resolution. Lower left: velocity [ 91 ] of Indian tectonic plate. PETM = Paleocene Eocene Thermal Maximum; EECO = Early Eocene Climatic Optimum; Oi-1 marks the transition to glaciated Antarctica; MCO = Miocene Climatic Optimum; NAIP = North Atlantic Igneous Province.

This equation is used for the early Cenozoic, up to the large-scale glaciation of Antarctica at ∼34 MyBP (Oi-1in Fig. 6 ). At larger δ 18 O (colder climate), lighter 16 O evaporates preferentially from the ocean and accumulates in ice sheets. In Zachos data, δ 18 O increases by 3 between Oi-1 and the LGM. Half of this δ 18 O change is due to the 6°C change of deep ocean temperature between Oi-1 (5°C) and the LGM (–1°C) [ 92 ]. The other 1.5 of δ 18 O change is presumed to be due to the ∼180 m sea level (SL) change between ice-free Earth and the LGM, with ∼60 m from Antarctic ice and 120 m from Northern Hemisphere ice. Thus, as an approximation to extract both SL and T do from δ 18 O, Hansen et al . [ 66 ] assumed that SL rose linearly by 60 m as δ 18 O increased from 1.75 to 3.25 and linearly by 120 m as δ 18 O increased from 3.25 to 4.75.

Zachos and Westerhold δ 18 O, SL and T do for the full Cenozoic, Pleistocene, and the past 800 000 years are graphed in Supplementary Material and sea level is compared to data of Rohling et al . [ 94 ]. We focus on the finer resolution W data. Differences between the W and Z data and interpretation of those differences are discussed in Paleocene Eocene Thermal Maximum section.

Cenozoic T S

In this section we combine the rich detail in T do provided by benthic δ 18 O with constraints on the range of Cenozoic T S from surface proxies to produce an estimated history of Cenozoic T S .

We expect T do change, which derives from sea surface temperature (SST) at high latitudes where deepwater forms, to approximate T S change when T do is not near the freezing point. Global SST change understates global T S (land plus ocean) change because land temperature response to a forcing exceeds SST response [ 95 ], e.g. the equilibrium global SST response of the GISS (2020) GCM to 2 × CO 2 is 70.6% of the global (land plus ocean) response. However, polar amplification of the SST response tends to compensate for SST undershoot of global T S change. Compensation is nearly exact at latitudes of North Atlantic deepwater formation for 2 × CO 2 climate change in the GISS (2020) climate model ( Fig. 7a ), but Southern Hemisphere polar amplification does not fully cover the 60–75°S latitudes where Antarctic bottom water forms.

(a) Ratio of ΔSST (latitude) to global TS change for all ocean and the Atlantic Ocean, based on equilibrium response (years 4001–4500) in 2 × CO2 simulations of GISS (2020) model. (b) ΔT, the amount by which TS change exceeds Tdo change, based on an exponential fit to the two data points provided by the Holocene and LGM (see text).

( a ) Ratio of ΔSST (latitude) to global T S change for all ocean and the Atlantic Ocean, based on equilibrium response (years 4001–4500) in 2 × CO 2 simulations of GISS (2020) model. ( b ) ΔT, the amount by which T S change exceeds T do change, based on an exponential fit to the two data points provided by the Holocene and LGM (see text).

Cenozoic temperature based on linear (Equations 15 and 16) and nonlinear (Equation 17) analyses. Antarctic Dome C data [40] (red) relative to last 1000 years are multiplied by 0.6 to account for polar amplification and 14°C is added for absolute scale.

Cenozoic temperature based on linear ( Equations 15 and 16 ) and nonlinear ( Equation 17 ) analyses. Antarctic Dome C data [ 40 ] (red) relative to last 1000 years are multiplied by 0.6 to account for polar amplification and 14°C is added for absolute scale.

The result is a consistent analysis of global T S for the entire Cenozoic ( Fig. 8b ). Oxygen isotope δ 18 O of deep ocean foraminifera reproduces glacial-interglacial temperature change well; more detailed agreement is not expected as Antarctic ice core data are for a location that moves, especially in altitude. Our interest is in warmer global climate and its relevance to upcoming human-caused climate change. For that purpose, we want to know the forcing that drove Cenozoic climate change. With the assumption that non-CO 2 GHG forcings provide 20% of the total GHG forcing, it is not difficult to infer the CO 2 abundance required to cause the Cenozoic temperature history in Fig. 8b . Considering the large disagreement among proxy CO 2 measures, this indirect measure of CO 2 via global T S may provide the most accurate Cenozoic CO 2 history.

Cenozoic CO 2

All quantities are known except ΔF CO2 (t), which is thus defined. Cenozoic CO 2 (t) for specified ECS is obtained from T S (t) using the CO 2 radiative forcing equation ( Table 1 , Supplementary Material ). Resulting CO 2 ( Fig. 9 ) is about 1,200 ppm at the EECO, 450 ppm at Oi-1, and 325 ppm in the Pliocene for ECS = 1.2°C per W/m 2 . For ECS = 1°C—about as low as we believe plausible—Pliocene CO 2 is near 350 ppm, rising only to ∼500 ppm at Oi-1 and ∼1500 ppm at EECO.

Cenozoic CO2 estimated from δ18O of Westerhold et al. (see text). Black lines are for ECS = 1.2°C per W/m2; red and green curves (ECS = 1.0 and 1.4°C per W/m2) are 1 My smoothed. Blue curves (last 800 000 years) are Antarctica ice core data [41].

Cenozoic CO 2 estimated from δ 18 O of Westerhold et al . (see text). Black lines are for ECS = 1.2°C per W/m 2 ; red and green curves (ECS = 1.0 and 1.4°C per W/m 2 ) are 1 My smoothed. Blue curves (last 800 000 years) are Antarctica ice core data [ 41 ].

Assumed Holocene CO 2 amount is also a minor factor. We tested two cases: 260 and 278 ppm ( Fig. 9 ). These were implemented as the CO 2 values at 7 kyBP, but Holocene-mean values are similar—a few ppm less than CO 2 at 7 kyBP. Holocene = 278 ppm increases CO 2 about 20 ppm between today and Oi-1, and about 50 ppm at the EECO. However, Holocene CO 2 278 ppm causes the amplitude of inferred glacial-interglacial CO 2 oscillations to be less than reality ( Fig. 9b ), providing support for the Holocene 260 ppm level and for the interpretation that high late-Holocene CO 2 was due to human influence. Proxy measures of Cenozoic CO 2 yield a notoriously large range. A recent review [ 88 ] constructs a CO 2 history with Loess-smoothed CO 2 ∼700–1100 ppm at Oi-1. That high Oi-1 CO 2 amount is not plausible without overthrowing the concept that global temperature is a response to climate forcings. More generally, we conclude that actual CO 2 during the Cenozoic was near the low end of the range of proxy measurements.

Interpretation of Cenozoic T S and CO 2

In this section we consider Cenozoic T S and CO 2 histories, which are rich in insights about climate change with implications for future climate.

In Target CO 2 [ 60 ] and elsewhere [ 98 ] we argue that the broad sweep of Cenozoic temperature is a result of plate tectonic (popularly ‘continental drift’) effects on CO 2 . Solid Earth sources and sinks of CO 2 are not balanced at any given time. CO 2 is removed from surface reservoirs by: (1) chemical weathering of rocks with deposition of carbonates on the ocean floor, and (2) burial of organic matter [ 99 , 100 ]. CO 2 returns via metamorphism and volcanic outgassing at locations where oceanic crust is subducted beneath moving continental plates. The interpretation in Target CO 2 was that the main Cenozoic source of CO 2 was associated with the Indian plate ( Fig. 10 ), which separated from Pangea in the Cretaceous [ 101 , 102 ] and moved through the Tethys (now Indian) Ocean at a rate exceeding 10 cm/year until collision with the Eurasian plate at circa 50 MyBP. Associated CO 2 emissions include those from formation of the Deccan Traps 7 in western India (a large igneous province, LIP, formed by repeated deposition of large-scale flood basalts), the smaller Rajahmundry Traps [ 103 ] in eastern India, and metamorphism and vulcanism associated with the moving Indian plate. The Indian plate slowed circa 60 Mya (inset, Fig. 6 ) before resuming high speed [ 91 ], leaving an indelible signature in the Cenozoic δ 18 O history ( Fig. 6 ) that supports our interpretation of the CO 2 source. Since the continental collision, subduction and CO 2 emissions continue at a diminishing rate as the India plate underthrusts the Asian continent and pushes up the Himalayan mountains [ 104 ]. We interpret the decline of CO 2 over the past 50 million years as, at least in part, a decline of the metamorphic source from continued subduction of the Indian plate, but burial of organic matter and increased weathering due to exposure of fresh rock by Himalayan uplift [ 105 ] may contribute to CO 2 drawdown. Quantitative understanding of these processes is limited [ 106 ], e.g. weathering is both a source and sink of CO 2 [ 107 ].

Continental configuration 56 MyBP [97]. Continental shelves (light blue) were underwater as little water was locked in ice. The Indian plate was moving north at about 15 cm per year.

Continental configuration 56 MyBP [ 97 ]. Continental shelves (light blue) were underwater as little water was locked in ice. The Indian plate was moving north at about 15 cm per year.

This picture for the broad sweep of Cenozoic CO 2 is consistent with current understanding of the long-term carbon cycle [ 108 ], but relative contributions of metamorphism [ 106 ] and volcanism [ 109 ] are uncertain. Also, emissions from rift-induced Large Igneous Provinces (LIPs) [ 110 , 111 ] contribute to long-term change of atmospheric CO 2 , with two cases prominent in Fig. 6 . The Columbia River Flood Basalt at ca. 17–15 MyBP was a principal cause of the Miocene Climatic Optimum [ 112 ], but the processes are poorly understood [ 113 ]. A more dramatic event occurred as Greenland separated from Europe, causing a rift in the sea floor; flood basalt covered more than a million square kilometers with magma volume 6–7 million cubic kilometers [ 111 ]—the North Atlantic Igneous Province (NAIP). Flood basalt volcanism occurred during 60.5–54.5 MyBP, but at 56.1 ± 0.5 MyBP melt production increased by more than a factor of 10, continued at a high level for about a million years, and then subsided ( Fig. 5 of Storey et al . [ 114 ]). The striking Paleocene-Eocene Thermal Maximum (PETM) δ 18 O spike ( Fig. 6 ) occurs early in this million-year bump-up of δ 18 O. Svensen et al . [ 115 ] proposed that the PETM was initiated by the massive flood basalt into carbon-rich sedimentary strata. Gutjahr et al . [ 116 ] developed an isotope analysis, concluding that most of PETM carbon emissions were volcanic, with climate-driven carbon feedbacks playing a lesser role. Yet other evidence [ 117 ], while consistent with volcanism as a trigger for the PETM, suggests that climate feedback—perhaps methane hydrate and peat CO 2 release—may have caused more than half of the PETM warming. Berndt et al . [ 118 ] describe extensive shallow-water vents that likely released CH 4 as well as CO 2 during the NAIP activity. We discuss PETM warming and CO 2 levels below, but first we must quantify the mechanisms that drove Cenozoic climate change and consider where Earth’s climate was headed before humanity intervened.

The sum of climate forcings (CO 2 and solar) and slow feedbacks (ice sheets and non-CO 2 GHGs) that maintained EECO warmth was 12.5 W/m 2 ( Fig. 11 ). CO 2 forcing of 9.1 W/m 2 combined with solar forcing of—1.2 W/m 2 to yield a total forcing 8 8 W/m 2 . Slow feedbacks were 4.5 W/m 2 forcing (ice albedo = 2 W/m 2 and non-CO 2 GHGs = 2.5 W/m 2 ). With today’s solar irradiance, human-made GHG forcing required for Earth to return to EECO warmth is 8 W/m 2 . Present human-made GHG forcing is 4.6 W/m 2 relative to 7 kyBP. 9 Equilibrium response to this forcing includes the 2 W/m 2 ice sheet feedback and 25% amplification (of 6.6 W/m 2 ) by non-CO 2 GHGs, yielding a total forcing plus slow feedbacks of 8.25 W/m 2 . Thus, equilibrium global warming for today’s GHGs is 10°C. 10 If human-made aerosol forcing is −1.5 W/m 2 and remains at that level indefinitely, equilibrium warming for today’s atmosphere is reduced to 8°C. Either 10°C or 8°C dwarfs observed global warming of 1.2°C to date. Most of the equilibrium warming for today’s atmosphere has not yet occurred and need not occur (Earth’s energy imbalance section).

Climate forcings and slow feedbacks relative to 7 kyBP from terms in Equations (21–23).

Climate forcings and slow feedbacks relative to 7 kyBP from terms in Equations (21–23) .

Prospects for another snowball Earth

We would be remiss if we did not comment on the precipitous decline of Earth’s temperature over the last several million years. Was Earth falling off the table into another Snowball Earth?

Global temperature plummeted in the past 50 million years, with growing, violent, oscillations ( Figs 6 and 7 ). Glacial-interglacial average CO 2 declined from about 325 ppm to 225 ppm in the past five million years in an accelerating decline ( Fig. 9a ). As CO 2 fell to 180 ppm during recent glacial maxima, an ice sheet covered most of Canada and reached midlatitudes in the U.S. Continents in the current supercontinent cycle [ 101 ] are now dispersed, with movement slowing to 2–3 cm/year. Emissions from the last high-speed high-impact tectonic event—collision of the Indian plate with Eurasia—are fizzling out. The most recent large igneous province (LIP) event—the Columbia River Flood Basalt about 15 million years ago ( Fig. 6 )—is no longer a factor, and there is no evidence of another impending LIP. Snowball conditions are possible, even though the Sun’s brightness is increasing and is now almost 6% greater [ 69 ] than it was at the last snowball Earth, almost 600 million years ago [ 68 ]. Runaway snowball likely requires only 1–2 halvings [ 66 ] of CO 2 from the LGM 180 ppm level, i.e. to 45–90 ppm. Although the weathering rate declines in colder climate [ 119 ], weathering and burial of organic matter continue, so decrease of atmospheric CO 2 could have continued over millions of years, if the source of CO 2 from metamorphism and vulcanism continued to decline.

Another factor that may have contributed to cooling in the Pliocene is uplift and poleward movement of Greenland that accelerated about 5 MyBP [ 120 ], which likely enhanced glaciation of Greenland and should be accounted for in simulations of Pliocene climate change. We conclude that, in the absence of human activity, Earth may have been headed for snowball Earth conditions within the next 10 or 20 million years, but the chance of future snowball Earth is now academic. Human-made GHG emissions remove that possibility on any time scale of practical interest. Instead, GHG emissions are now driving Earth toward much warmer climate.

Paleocene eocene thermal maximum (PETM)

The PETM event provides a benchmark for assessing the potential impact of the human-made climate forcing and the time scale for natural recovery of the climate system.

Westerhold [ 90 ] data have 10°C deep ocean warming at the PETM ( Figs 8 and 12a ), which exceeds proxy-derived surface warming. Low latitude SST data have 3–4°C PETM warming [ 121 ]. Tierney et al . [ 122 ] obtain PETM global surface warming 5.6°C (5.4–59°C, 95% confidence) via analysis of proxy surface temperature data that accounts for patterns of temperature change. Zachos [ 44 ] data have a deep ocean warming similar to the proxy-based surface warming. These warming estimates can be reconciled, but first let’s note the practical importance of the PETM.

Pre-PETM (56–56.4 MyBP) CO 2 is 910 ppm in our analysis for the most likely ECS (1.2°C per W/m 2 ). Peak PETM CO 2 required to yield the 5.6°C global surface warming estimate of Tierney et al . [ 122 ] is then 1630 ppm if CO 2 provides 80% of the GHG forcing, thus less than a doubling of CO 2 . (In the unlikely case that CO 2 caused 100% of the GHG forcing, required CO 2 is 1780, not quite a doubling.) CO 2 amounts for ECS = 1.0 and 1.4°C per W/m 2 are 1165 and 760 ppm in the pre-PETM and 2260 and 1270 ppm at peak PETM, respectively. In all these ECS cases, the CO 2 forcing of the PETM is less than or about a CO 2 doubling. Our assumed 20% contribution by non-CO 2 GHGs (amplification factor 1.25, Climate sensitivity (ECS and ESS) section), is nominal; Hopcroft et al ., e.g. estimate a 30% contribution from non-CO 2 GHGs [ 123 ], thus an amplification factor 1.43.

Thus, today’s human-made GHG forcing (4.6 W/m 2 , growing 0.5 W/m 2 per decade) is already at least comparable to the PETM forcing, although the net human-made forcing including aerosols has probably not reached the PETM forcing. However, there are two big differences between the PETM and today. First, there were no large ice sheets on Earth in the PETM era. Ice sheets on Antarctica and Greenland today make Earth system sensitivity (ESS) greater than it was during the PETM. Equilibrium response to today’s GHG climate forcing would include deglaciation of Antarctica and Greenland, sea level rise of 60 m (200 feet), and surface albedo forcing (slow feedback) of 2 W/m 2 . The second difference between the PETM and today is the rate of change of the climate forcing. Most of today’s climate forcing was introduced in a century, which is 10 times or more faster than the PETM forcing growth. Although a bolide impact [ 124 ] has been proposed as a trigger for the PETM, the issue is the time scale on which the climate forcing—increased GHGs—occurred. Despite uncertainty in the carbon source(s), data and modeling point to duration of a millennium or more for PETM emissions [ 121 , 125 ].

Better understanding of the PETM could inform us on climate feedbacks. Gutjahr et al . [ 116 ] argue persuasively that PETM emissions were mostly volcanic, yet we know of no other large igneous province that produced such great, temporally-isolated, emissions. Further, Cenozoic orbitally-driven hyperthermal events [ 126 ] testify to large CO 2 feedbacks. Northern peatlands today contain more than 1000 Gt carbon [ 127 ], much of which can be mobilized at PETM warming levels [ 128 ]. The double peak in deep ocean δ 18 O (thus in temperature, cf. Fig. 12 , where each square is a binning interval of 5000 years) is also found in terrestrial data [ 129 ]. Perhaps the sea floor rift occurred in two bursts, or the rift was followed tens of thousands of years later by methane hydrate release as a feedback to the ocean warming; much of today’s methane hydrate is in stratigraphic deposits hundreds of meters below the sea floor, where millennia may pass before a thermal wave from the surface reaches the deposits [ 130 ]. Feedback emissions, especially from permafrost, seem to be more chronic than catastrophic, but stabilization of climate may require cooling that terminates growth of those feedbacks (Summary section). The PETM provides perhaps the best empirical check on understanding of the atmospheric lifetime of fossil fuel CO 2 [ 131 ], but for that purpose we must untangle as well as possible the time dependence of the PETM CO 2 source and feedbacks. If continuing magma flow or a slow-release feedback is a substantial portion of PETM CO 2 , the CO 2 lifetime inferred from post-PETM CO 2 recovery may be an exaggeration.

Temperature and CO2 implied by Westerhold et al. [90] δ18O, if surface warming equaled deep ocean warming. In reality, the unique PETM event had surface warming ∼5.6°C, which implies a peak PETM CO2 of about 1630 ppm (see text).

Temperature and CO 2 implied by Westerhold et al . [ 90 ] δ 18 O, if surface warming equaled deep ocean warming. In reality, the unique PETM event had surface warming ∼5.6°C, which implies a peak PETM CO 2 of about 1630 ppm (see text).

The PETM draws attention to differences between the Westerhold (W) and Zachos (Z) δ 18 O data. Zachos attributes the larger PETM response in W data to the shallow (less than 1 km) depth of the Walvis Ridge core in the Southeast Atlantic that anchors the PETM period in the W data (see Supplementary Material SM9 ). Given that the PETM was triggered by a rift in the floor of the North Atlantic and massive lava injection, it is not surprising that ocean temperature was elevated and circulation disrupted during the PETM. Nunes and Norris [ 132 ] conclude that ocean circulation changed at the start of the PETM with a shift in location of deep-water formation that delivered warmer waters to the deep sea, a circulation change that persisted at least 40 000 years. With regard to differences in the early Cenozoic, Zachos notes ( Supplementary Material SM9 ) a likely bias in the Z data with a heavy weighting of data from Southern Ocean sites (Kerguelen Plateau and Maud Rise), which were intended for study of climate of Antarctica and the Southern Ocean.

Differences between the W and Z data sets have limited effect on our paper, as we apply separate scaling ( Equations 7–14 ) to W and Z data to match observations at the LGM, mid-Holocene, and Oi-1 points. This approach addresses, e.g. the cumulative effect in combining data splices noted by Zachos in SM9. Further, we set the EECO global temperature relative to the Holocene and the PETM temperature relative to pre-PETM based on proxy-constrained, full-field, GCM analyses of Tierney et al . [ 122 ] and Zhu et al . [ 96 ] Nevertheless, there is much to learn from more precise study of the Cenozoic in general and the PETM in particular.

Policy implications require first an understanding of the role of aerosols in climate change.

The role of aerosols in climate change is uncertain because aerosol properties are not measured well enough to define their climate forcing. In this section we estimate aerosol climate forcing via aerosol effects on Earth’s temperature and Earth’s energy imbalance.

Aerosol impact is suggested by the gap between observed global warming and expected warming due to GHGs based on ECS inferred from paleoclimate ( Fig. 13 ). Expected warming is from Eq. 5 with the normalized response function of the GISS (2020) model. Our best estimate for ECS, 1.2°C per W/m 2 , yields a gap of 1.5°C between expected and actual warming in 2022. Aerosols are the likely cooling source. The other negative forcing discussed by IPCC—surface albedo change—is estimated by IPCC (Chapter 7, Table 7.8) to be –0.12 ± 0.1 W/m 2 , an order of magnitude smaller than aerosol forcing [ 12 ]. Thus, for clarity, we focus on GHGs and aerosols.

Observed global surface temperature (black line) and expected GHG warming with two choices for ECS. The blue area is the estimated aerosol cooling effect. The temperature peak in the World War II era is in part an artifact of inhomogeneous ocean data in that period [63].

Observed global surface temperature (black line) and expected GHG warming with two choices for ECS. The blue area is the estimated aerosol cooling effect. The temperature peak in the World War II era is in part an artifact of inhomogeneous ocean data in that period [ 63 ].

Absence of global warming over the period 1850–1920 ( Supplementary Fig. S1 of IPCC AR6 WG1 report [ 12 ]) is a clue about aerosol forcing. GHG forcing increased 0.54 W/m 2 in 1850–1920, which causes expected warming 0.3–0.4°C by 1920 for ECS = 1.2°C per W/m 2 ( Equation 5 ). Natural forcings—solar irradiance and volcanoes—may contribute to lack of warming, but a persuasive case for the required forcing has not been made. Human-made aerosols are the likely offset of GHG warming. Such aerosol cooling is a Faustian bargain [ 98 ] because payment in enhanced global warming will come due once we can no longer tolerate the air pollution. Ambient air pollution causes millions of deaths per year, with particulates most responsible [ 133 , 134 ].

Evidence of aerosol forcing in the Holocene

In this section we infer evidence of human-made aerosols in the last half of the Holocene from the absence of global warming. Some proxy-based analyses [ 135 ] report cooling in the last half of the Holocene, but a recent analysis [ 50 ] that uses GCMs to overcome spatial and temporal biases in proxy data finds rising global temperature in the first half of the Holocene followed by nearly constant temperature in the last 6000 years until the last few centuries ( Fig. 14 ). Antarctic, deep ocean, and tropical sea surface data all show stable temperature in the last 6000 years ( Supplementary Fig. S6 of reference [ 60 ]). GHG forcing increased 0.5 W/m 2 during those 6000 years ( Fig. 15 ), yet Earth did not warm. Fast feedbacks alone should yield at least +0.5°C warming and 6000 years is long enough for slow feedbacks to also contribute. How can we interpret the absence of warming?

Global mean surface temperature change over the past 24 ky, reproduced from Fig. 2 of Osman et al. [50] including Last Millennium reanalysis of Tardif et al. [136].

Global mean surface temperature change over the past 24 ky, reproduced from Fig. 2 of Osman et al . [ 50 ] including Last Millennium reanalysis of Tardif et al . [ 136 ].

GHG climate forcing in past 20 ky with vertical scale expanded for the past 10 ky on the right. GHG amounts are from Schilt et al. [47]. Formulae for forcing are in Supplementary Material.

GHG climate forcing in past 20 ky with vertical scale expanded for the past 10 ky on the right. GHG amounts are from Schilt et al . [ 47 ]. Formulae for forcing are in Supplementary Material .

Humanity’s growing footprint deserves scrutiny. Ruddiman’s suggestion that deforestation and agriculture began to affect CO 2 6500 year ago and rice agriculture began to affect CH 4 5000 years ago has been criticized [ 46 ] mainly because of the size of proposed sources. Ruddiman sought sources sufficient to offset declines of CO 2 and CH 4 in prior interglacial periods, but such large sources are not needed to account for Holocene GHG levels. Paleoclimate GHG decreases are slow feedbacks that occur in concert with global cooling. However, if global cooling did not occur in the past 6000 years, feedbacks did not occur. Earth orbital parameters 6000 years ago kept the Southern Ocean warm, as needed to maintain strong overturning ocean circulation [ 137 ] and minimize carbon sequestration in the deep ocean. Maximum insolation at 60°S was in late-spring (mid-November); since then, maximum insolation at 60°S slowly advanced through the year, recently reaching mid-summer (mid-January, Fig. 26b of Ice Melt [ 13 ]). Maximum insolation from late-spring through mid-summer is optimum to warm the Southern Ocean and promote early warm-season ice melt, which reduces surface albedo and magnifies regional warming [ 45 ].

GHG forcing of –0.2 W/m 2 in 10–6 kyBP ( Fig. 15 ) was exceeded by forcing of +1 W/m 2 due to ice sheet shrinkage ( Supplementary Material in Target CO 2 [ 60 ]) for a 40 m sea level rise ( Fig. 16 ). Net 0.8 W/m 2 forcing produced expected 1°C global warming ( Fig. 14 ). The mystery is the absence of warming in the past 6000 years. Hansen et al . [ 45 ] suggested that aerosol cooling offset GHG warming. Growing population, agriculture and land clearance produced aerosols and CO 2 ; wood was the main fuel for cooking and heating. Nonlinear aerosol forcing is largest in a pristine atmosphere, so it is unsurprising that aerosols tended to offset CO 2 warming as civilization developed. Hemispheric differences could provide a check. GHG forcing is global, while aerosol forcing is mainly in the Northern Hemisphere. Global offset implies a net negative Northern Hemisphere forcing and positive Southern Hemisphere forcing. Thus, data and modeling studies (including orbital effects) of regional response are warranted but beyond the scope of this paper.

Sea level since the last glacial period relative to present. Credit: Robert Rohde [138].

Sea level since the last glacial period relative to present. Credit: Robert Rohde [ 138 ].

Industrial era aerosols

Scientific advances often face early resistance from other scientists [ 139 ]. Examples are the snowball Earth hypothesis [ 140 ] and the role of an asteroid impact in extinction of non-avian dinosaurs [ 141 ], which initially were highly controversial but are now more widely accepted. Ruddiman’s hypothesis, right or wrong, is still controversial. Thus, we minimize this issue by showing aerosol effects with and without preindustrial human-made aerosols.

Global aerosols are not monitored with detail needed to define aerosol climate forcing [ 142 , 143 ]. IPCC12 estimates forcing ( Fig. 17a ) from assumed precursor emissions, a herculean task due to many aerosol types and complex cloud effects. Aerosol forcing uncertainty is comparable to its estimated value ( Fig. 17a ), which is constrained more by observed global temperature change than by aerosol measurements [ 144 ]. IPCC’s best estimate of aerosol forcing ( Fig. 17 ) and GHG history define the percent of GHG forcing offset by aerosol cooling—the dark blue area in Fig. 17b . However, if human-made aerosol forcing was −0.5 W/m 2 by 1750, offsetting +0.5 W/m 2 GHG forcing, this forcing should be included. Such aerosol forcing—largely via effects of land use and biomass fuels on clouds—continues today. Thirty million people in the United States use wood for heating [ 145 ]. Such fuels are also common in Europe [ 146 , 147 ] and much of the world.

(a) Estimated greenhouse gas and aerosol forcings relative to 1750 values. (b) Aerosol forcing as percent of GHG forcing. Forcings for dark blue area are relative to 1750. Light blue area adds 0.5 W/m2 forcing estimated for human-caused aerosols from fires, biofuels and land use.

( a ) Estimated greenhouse gas and aerosol forcings relative to 1750 values. ( b ) Aerosol forcing as percent of GHG forcing. Forcings for dark blue area are relative to 1750. Light blue area adds 0.5 W/m 2 forcing estimated for human-caused aerosols from fires, biofuels and land use.

Figure 17b encapsulates two alternative views of aerosol history. IPCC aerosol forcing slowly becomes important relative to GHG forcing. In our view, civilization always produced aerosols as well as GHGs. As sea level stabilized, organized societies and population grew as coastal biologic productivity increased [ 148 ] and agriculture developed. Wood was the main fuel. Aerosols travel great distances, as shown by Asian aerosols in North America [ 149 ]. Humans contributed to both rising GHG and aerosol climate forcings in the past 6000 years. One result is that human-caused aerosol climate forcing is at least 0.5 W/m 2 more than usually assumed. Thus, the Faustian payment that will eventually come due is also larger, as discussed in Summary section.

Ambiguity in aerosol climate forcing

In this section we discuss uncertainty in the aerosol forcing. We discuss why global warming in the past century—often used to infer climate sensitivity—is ill-suited for that purpose.

Recent global warming does not yield a unique ECS because warming depends on three major unknowns with only two basic constraints. Unknowns are ECS, net climate forcing (aerosol forcing is unmeasured), and ocean mixing (many ocean models are too diffusive). Constraints are observed global temperature change and Earth’s energy imbalance (EEI) [ 80 ]. Knutti [ 150 ] and Hansen [ 75 ] suggest that many climate models compensate for excessive ocean mixing (which reduces surface warming) by using aerosol forcing less negative than the real world, thus achieving realistic surface warming. This issue is unresolved and complicated by the finding that cloud feedbacks can buffer ocean heat uptake (Climate response time section), affecting interpretation of EEI.

IPCC AR6 WG1 best estimate of aerosol forcing (Table AIII.3) [ 12 ] is near maximum (negative) value by 1975, then nearly constant until rising in the 21st century to –1.09 W/m 2 in 2019 ( Fig. 18 ). We use this IPCC aerosol forcing in climate simulations here. We also use an alternative aerosol scenario [ 151 ] that reaches –1.63 W/m 2 in 2010 relative to 1880 and –1.8 W/m 2 relative to 1850 ( Fig. 18 ) based on modeling of Koch [ 152 ] that included changing technology factors defined by Novakov [ 153 ]. This alternative scenario 11 is comparable to the forcing in some current aerosol models ( Fig. 18 ). Human-made aerosol forcing relative to several millennia ago may be even more negative, by about –0.5 W/m 2 as discussed above, but the additional forcing was offset by increasing GHGs and thus those additional forcings are neglected, with climate assumed to be in approximate equilibrium in 1850.

Aerosol forcing relative to 1850 from IPCC AR6, an alternative aerosol scenario [151] two aerosol model scenarios of Bauer et al. [154].

Aerosol forcing relative to 1850 from IPCC AR6, an alternative aerosol scenario [ 151 ] two aerosol model scenarios of Bauer et al . [ 154 ].

Many combinations of climate sensitivity and aerosol forcing can fit observed global warming. The GISS (2014) model (ECS = 2.6°C) with IPCC AR6 aerosol forcing can match observed warming ( Fig. 19 ) in the last half century (when human-made climate forcing overwhelmed natural forcings, unforced climate variability, and flaws in observations). However, agreement also can be achieved by climate models with high ECS. The GISS (2020) model (with ECS = 3.5°C) yields greater warming than observed if IPCC aerosol forcing is used, but less than observed for the alternative aerosol scenario ( Fig. 19 ). This latter aerosol scenario achieves agreement with observed warming if ECS ∼4°C (green curve in Fig. 19 ). 12 Agreement can be achieved with even higher ECS by use of a still more negative aerosol forcing.

Global temperature change TG due to aerosols + GHGs calculated with Green’s function Equation (5) using GISS (2014) and GISS (2020) response functions (Fig. 4). Observed temperature is the NASA GISS analysis [155, 156]. Base period: 1951–1980 for observations and model.

Global temperature change T G due to aerosols + GHGs calculated with Green’s function Equation (5) using GISS (2014) and GISS (2020) response functions ( Fig. 4 ). Observed temperature is the NASA GISS analysis [ 155 , 156 ]. Base period: 1951–1980 for observations and model.

The issue we raise is the magnitude of the aerosol forcing, with implications for future warming when particulate air pollution is likely to be reduced. We suggest that IPCC reports may have gravitated toward climate sensitivity near 3°C for 2 × CO 2 in part because of difficulty that models have in realistically simulating amplifying cloud feedbacks and a climate model tendency for excessive mixing of heat into the deep ocean. Our finding from paleoclimate analysis that ECS is 1.2°C ± 0.3°C per W/m 2 (4.8°C ± 1.2°C for 2 × CO 2 ) implies that the (unmeasured) aerosol forcing must be more negative than IPCC’s best estimate. In turn—because aerosol-cloud interactions are the main source of uncertainty in aerosol forcing—this finding emphasizes the need to measure both global aerosol and cloud particle properties.

The case for monitoring global aerosol climate forcing will grow as recognition of the need to slow and reverse climate change emerges. Aerosol and cloud particle microphysics must be measured with precision adequate to define the forcing [ 142 , 158 ]. In the absence of such Keeling-like global monitoring, progress can be made via more limited satellite measurements of aerosol and cloud properties, field studies, and aerosol and cloud modeling. As described next, a great opportunity to study aerosol and cloud physics is provided by a recent change in the IMO (International Maritime Organization) regulations on ship emissions.

The great inadvertent aerosol experiment

Sulfate aerosols are cloud condensation nuclei (CCN), so sulfate emissions by ships result in a larger number of smaller cloud particles, thus affecting cloud albedo and cloud lifetime [ 144 ]. Ships provide a large percentage of sulfates in the North Pacific and North Atlantic regions ( Fig. 20 ). It has been suggested that cooling by these clouds is overestimated because of cloud liquid water adjustments [ 159 ], but Manshausen et al . [ 160 ] present evidence that liquid water path (LWP) effects are substantial even in regions without visible ship-tracks; they estimate a LWP forcing −0.76 ± 0.27 W/m 2 , in stark contrast with the IPCC estimate of +0.2 ± 0.2 W/m 2 . Wall et al . [ 161 ] use satellite observations to quantify relationships between sulfates and low-level clouds; they estimate a sulfate indirect aerosol forcing of −1.11 ± 0.43 W/m 2 over the global ocean. The range of aerosol forcings used in CMIP6 and AR6 GCMs (small blue bar in Fig. 18 ) is not a measure of aerosol forcing uncertainty. The larger bar, from Chapter 7 [ 162 ] of AR6, has negative forcing as great as –2 W/m 2 , but even that does not measure the full uncertainty.

Total sulfate (parts per trillion by volume) and percentage of total sulfate provided by shipping in simulations of Jin et al. [157] prior to IMO regulations on sulfur content of fuels.

Total sulfate (parts per trillion by volume) and percentage of total sulfate provided by shipping in simulations of Jin et al . [ 157 ] prior to IMO regulations on sulfur content of fuels.

Changes of IMO emission regulations provide a great opportunity for insight into aerosol climate forcing. Sulfur content of fuels was limited to 1% in 2010 near the coasts of North America and in the North Sea, Baltic Sea and English Channel, and further restricted there to 0.1% in 2015 [ 163 ]. In 2020 a limit of 0.5% was imposed worldwide. The 1% limit did not have a noticeable effect on ship-tracks, but a striking reduction of ship-tracks was found after the 2015 IMO regulations, especially in the regions near land where emissions were specifically limited [ 164 ]. Following the additional 2020 regulations [ 165 ], global ship-tracks were reduced more than 50% [ 166 ].

Earth’s albedo (reflectivity) measured by CERES (Clouds and Earth’s Radiant Energy System) satellite-borne instruments [ 81 ] over the 22-years March 2000 to March 2022 reveal a decrease of albedo and thus an increase of absorbed solar energy coinciding with the 2015 change of IMO emission regulations. Global absorbed solar energy is + 1.05 W/m 2 in the period January 2015 through December 2022 relative to the mean for the first 10 years of data ( Fig. 21 ). This increase is 5 times greater than the standard deviation (0.21 W/m 2 ) of annual absorbed solar energy in the first 10 years of data and 4.5 times greater than the standard deviation (0.23 W/m 2 ) of CERES data through December 2014. The increase of absorbed solar energy is notably larger than estimated potential CERES instrument drift, which is <0.085 W/m 2 per decade [ 81 ]. Increased solar energy absorption occurred despite 2015–2020 being the declining phase of the ∼11-year solar irradiance cycle [ 167 ]. Nor can increased absorption be attributed to correlation of Earth’s albedo (and absorbed solar energy) with the Pacific Decadal Oscillation (PDO): the PDO did shift to the positive phase in 2014–2017, but it returned to the negative phase in 2017–2022 [ 168 ].

Global absorbed solar radiation (W/m2) relative to mean of the first 120 months of CERES data. CERES data are available at http://ceres.larc.nasa.gov/order_data.php.

Global absorbed solar radiation (W/m 2 ) relative to mean of the first 120 months of CERES data. CERES data are available at http://ceres.larc.nasa.gov/order_data.php .

Given the large increase of absorbed solar energy, cloud changes are likely the main cause. Quantitative analysis [ 168 ] of contributions to the 20-year trend of absorbed solar energy show that clouds provide most of the change. Surface albedo decrease due to sea ice decline contributes to the 20-year trend in the Northern Hemisphere, but that sea ice decline occurred especially in 2007, with minimum sea ice cover reached in 2012; over the past decade as global and hemispheric albedos declined, sea ice had little trend [ 169 ]. Potential causes of the cloud changes include: (1) reduced aerosol forcing, (2) cloud feedbacks to global warming, (3) natural variability [ 170 ]. Absorbed solar energy was 0.77 W/m 2 greater in Jan2015-Dec2022 than in the first decade of CERES data at latitudes 20–60°S ( Fig. 22 ), a region of relatively little ship traffic. This change is an order of magnitude larger than the estimate of potential detector degradation [ 81 ].

Absorbed solar radiation for indicated regions relative to first 120 months of CERES data. Southern Hemisphere 20–60°S is 89% ocean. North Atlantic is (20–60°N, 0–60°W) and North Pacific is (20–60°N, 120–220°W). Data source: http://ceres.larc.nasa.gov/order_data.php.

Absorbed solar radiation for indicated regions relative to first 120 months of CERES data. Southern Hemisphere 20–60°S is 89% ocean. North Atlantic is (20–60°N, 0–60°W) and North Pacific is (20–60°N, 120–220°W). Data source: http://ceres.larc.nasa.gov/order_data.php .

Climate models predict a reduction of cloud albedo in this region as a feedback effect driven by global warming [ 12 ] (Sec. Continued monitoring of absorbed energy can confirm the reality of the change, but without global monitoring of detailed physical properties of aerosols and clouds [ 142 ], it will be difficult to apportion observed change among candidate causes.

North Pacific and North Atlantic regions of heavy ship traffic are ripe for detailed study of cloud changes and their causes, although unforced cloud variability is large in such sub-global regions. Both regions have increased absorption of solar radiation after 2015 ( Fig. 22 ). The 2014–2017 maximum absorption in the North Pacific is likely enhanced by reduced cloud cover during the positive PDO, but the more recent high absorption is during the negative PDO phase. In the North Atlantic, persistence of increased absorption for several years exceeds prior variability, but longer records plus aerosol and cloud microphysical data are needed for interpretation.

Climate change is characterized by delayed response and amplifying feedbacks. Delayed response makes human-made climate forcing a threat to today’s public and future generations because of the practical difficulty of reversing the forcing once consequences become apparent. Feedbacks determine climate sensitivity to any applied forcing. We find that Earth’s climate is very sensitive—more sensitive than the best estimate of the Intergovernmental Panel on Climate Change (IPCC)—which implies that there is a great amount of climate change ‘in the pipeline.’ Extraordinary actions are needed to reduce the net human-made climate forcing, as is required to reduce global warming and avoid highly undesirable consequences for humanity and nature.

Equilibrium climate sensitivity (ECS)

The 1979 Charney study [ 4 ] considered an idealized climate sensitivity in which ice sheets and non-CO 2 GHGs are fixed. The Charney group estimated that the equilibrium response to 2 × CO 2 , a forcing of 4 W/m 2 , was 3°C, thus an ECS of 0.75°C per W/m 2 , with one standard deviation uncertainty σ = 0.375°C. Charney’s estimate stood as the canonical ECS for more than 40 years. The current IPCC report [ 12 ] concludes that 3°C for 2 × CO 2 is their best estimate for ECS.

We compare recent glacial and interglacial climates to infer ECS with a precision not possible with climate models alone. Uncertainty about Last Glacial Maximum (LGM) temperature has been resolved independently with consistent results by Tierney et al . [ 49 ] and Seltzer et al . [ 51 ]. The Tierney approach, using a collection of geochemical temperature indicators in a global analysis constrained by climate change patterns defined by a global climate model, is used by Osman et al . [ 50 ] to find peak LGM cooling 7.0 ± 1°C (2σ, 95% confidence) at 21–18 kyBP. We show that, accounting for polar amplification, these analyses are consistent with the 5.8 ± 0.6°C LGM cooling of land areas between 45°S and 35°N found by Seltzer et al . using the temperature-dependent solubility of dissolved noble gases in ancient groundwater. The forcing that maintained the 7°C LGM cooling was the sum of 2.25 ± 0.45 W/m 2 (2σ) from GHGs and 3.5 ± 1.0 W/m 2 (2σ) from the LGM surface albedo, thus 5.75 ± 1.1 W/m 2 (2σ). ECS implied by the LGM is thus 1.22 ± 0.29°C (2σ) per W/m 2 , which, at this final step, we round to 1.2 ± 0.3°C per W/m 2 . For transparency, we have combined uncertainties via simple RMS (root-mean-square). ECS as low as 3°C for 2 × CO 2 is excluded at the 3σ level, i.e. with 99.7% confidence.

More sophisticated mathematical analysis, which has merits but introduces opportunity for prior bias and obfuscation, is not essential; error assessment ultimately involves expert judgment. Instead, focus is needed on the largest source of error: LGM surface albedo change, which is uncertain because of the effect of cloud shielding on the efficacy of the forcing. As cloud modeling is advancing rapidly, this topic is ripe for collaboration of CMIP [ 53 ] (Coupled Model Intercomparison Project) with PMIP [ 54 ] (Paleoclimate Modelling Intercomparison Project). Simulations should include at the same time change of surface albedo and topography of ice sheets, vegetation change, and exposure of continental shelves due to lower sea level.

Knowledge of climate sensitivity can be advanced further via analysis of the wide climate range in the Cenozoic era (Earth system sensitivity section). However, interpretation of data and models, and especially projections of climate change, depend on understanding of climate response time.

We expected climate response time—the time for climate to approach a new equilibrium after imposition of a forcing—to become faster as mixing of heat in ocean models improved [ 75 ]. That expectation was not met when we compared two generations of the GISS GCM (global climate model). The GISS (2020) GCM is improved [ 32 , 33 ] in its ocean simulation over the GISS (2014) GCM as a result of higher vertical and horizontal resolution, more realistic parameterization of sub-grid scale motions, and correction of errors in the ocean computer program [ 32 ]. Yet the time for the model to achieve 63% of its equilibrium response remained about 100 years. There are two reasons for this: one that is obvious and one that is more interesting and informative.

The surface in the newer model warms as fast as in the older model, but it must achieve greater warming to reach 63% of equilibrium because its ECS is higher, which is one reason that the response time remains long. The other reason is that Earth’s energy imbalance (EEI) in the newer model decreases rapidly. EEI defines the rate that heat is pumped into the ocean, so a smaller EEI implies a longer time for the ocean to reach its new equilibrium temperature. Quick drop of EEI—in the first year after introduction of the forcing—implies existence of ultrafast feedback in the GISS (2020) model. For want of an alternative with such a large effect on Earth’s energy budget, we infer a rapid cloud feedback and we suggest (Slow, fast and ultrafast feedbacks section) a set of brief GCM runs that define cloud changes and other diagnostic quantities to an arbitrary accuracy.

The Charney report [ 4 ] recognized that clouds were a main cause of a wide range in ECS estimates. Today, clouds still cast uncertainty on climate predictions. Several CMIP6 [ 34 ] GCMs have ECS of ∼4–6°C for 2×CO 2 [ 171 , 172 ] with the high sensitivity caused by cloud feedbacks [ 84 ]. As cloud modeling progresses, it will aid understanding if climate models report their 2 × CO 2 response functions for both temperature and EEI (Earth’s energy imbalance).

Fast EEI response—faster than global temperature response—has a practical effect: observed EEI understates the reduction of climate forcing required to stabilize climate. Although the magnitude of this effect is uncertain (see Supplementary Material SM6 ), it makes the task of restoring a hospitable climate and saving coastal cities more challenging. On the other hand, long climate response time implies the potential for educated policies to affect the climate outcome before the most undesirable consequences occur.

The time required for climate to reach a new equilibrium is relevant to policy (Perspective on policy implications section), but there is another response time of practical importance. With climate in a state of disequilibrium, how much time do we have before we pass the point of no return, the point where major climate impacts are locked in, beyond our ability to control? That’s a complex matter; it requires understanding of ‘slow’ feedbacks, especially ice sheets. It also depends on how far climate is out of equilibrium. Thus, we first consider the full Earth system sensitivity.

Earth system sensitivity (ESS)

The Cenozoic era—the past 66 million years—provides an opportunity to study Earth system sensitivity via a consistent analysis for climate ranging from hothouse conditions with Earth 15°C warmer and sea level 60 m higher than preindustrial climate to glacial conditions with Earth 7°C cooler and sea level 120 m lower than preindustrial. Atmospheric CO 2 amount in the past 800 000 years ( Fig. 2 ), confirms expectation that CO 2 is the main control knob [ 87 ] on global temperature. We can assume this control existed when CO 2 amount varied due to CO 2 emissions caused by plate tectonics (continental drift). The two-step [ 91 ] that the Indian plate executed as it moved through the Tethys (now Indian) ocean left a signature in atmospheric CO 2 and global temperature. CO 2 emissions from subduction of ocean crust were greatest when the Indian plate was moving fastest (inset, Fig. 6 ) and peaked at its hard collision with the Eurasian plate at 50 MyBP. Diminishing metamorphic CO 2 emissions continue as the Indian plate is subducted beneath the Eurasian plate, pushing up the Himalayan Mountains, but carbon drawdown from weathering and burial of organic carbon exceeds emissions. Motion of the Indian Plate thus dominates the broad sweep of Cenozoic CO 2 , but igneous provinces play a role. The North Atlantic Igneous Province (caused by a rift in the sea floor as Greenland pulled away from Europe) that triggered the Paleocene-Eocene Thermal Maximum (PETM) event about 56 MyBP and the Columbia River Flood Basalt about 15 MyBP ( Fig. 6 ) are most notable.

We infer the Cenozoic history of sea surface temperature (SST) at sites of deepwater formation from the oxygen isotope δ 18 O in shells of deep-ocean-dwelling foraminifera preserved in ocean sediments [ 44 , 90 ]. High latitude SST change—including a correction term as SST approaches the freezing point—provides an accurate estimate of global surface temperature change. This Cenozoic temperature history and climate sensitivity inferred from the LGM cooling yield an estimate of Cenozoic CO 2 history. We suggest that this whole-Cenozoic approach may define the CO 2 history ( Fig. 9a ) more accurately than CO 2 proxy measurements. We find CO 2 about 325 ppm in the early Pliocene and 450 ppm at transition to glaciated Antarctica. Global climate models (GCMs) that isolate on the Pliocene tend to use CO 2 levels of order 400 ppm in attempts to match actual Pliocene warmth and ice sheet models use CO 2 of order 700 ppm or greater to achieve ice sheet disintegration on Antarctica, which suggests that the models are not realistically capturing amplifying feedback processes (see Cenozoic CO 2 section).

The Cenozoic provides a perspective on present greenhouse gas (GHG) levels. The dashed line in Fig. 23 is the ‘we are here’ level of GHG climate forcing. Today’s GHG forcing of 4.6 W/m 2 is relative to mid-Holocene CO 2 of 260 ppm; we present evidence in Cenozoic CO 2 section that 260 ppm is the natural Holocene CO 2 level. Human-caused GHG forcing today is already above the level needed to deglaciate Antarctica, if such forcing is left in place long enough. We do not predict full deglaciation of Antarctica on a time scale people care about—rather we draw attention to how far today’s climate is out of equilibrium with today’s GHG level. This is one measure of how strongly humanity is pushing the climate system. Stabilizing climate requires removing the disequilibrium by reducing human-made climate forcing. A danger is that it will become difficult or implausible to prevent large sea level rise, if deglaciation is allowed to get well underway.

Forcing required to yield Cenozoic temperature for today’s solar irradiance, compared with human-made GHG forcing in 2022.

Forcing required to yield Cenozoic temperature for today’s solar irradiance, compared with human-made GHG forcing in 2022.

GHGs are not the only large human-made climate forcing. Understanding of ongoing climate change requires that we also include the effect of aerosols (fine airborne particles).

Aerosol climate forcing is larger than the IPCC AR6 estimate and has likely been significant for millennia. We know of no other persuasive explanation for absence of global warming in the last half of the Holocene ( Fig. 14 ) as GHG forcing increased 0.5 W/m 2 ( Fig. 15 ). Climate models without a growing negative aerosol forcing yield notable warming in that period [ 173 ], a warming that, in fact, did not occur. Negative aerosol forcing, increasing as civilization developed and population grew, is expected. As humans burned fuels at a growing rate—wood and other biomass for millennia and fossil fuels in the industrial era—aerosols as well as GHGs were an abundant, growing, biproduct. The aerosol source from wood-burning has continued in modern times [ 146 ]. GHGs are long-lived and accumulate, so their forcing dominates eventually, unless aerosol emissions grow higher and higher—the Faustian bargain [ 98 ].

Multiple lines of evidence show that aerosol forcing peaked early this century [ 174 ]. Emissions from the largest sources, China and India, were increasing in 2000, but by 2010 when the first limits on ship emissions were imposed, China’s emissions were declining. We estimate peak (negative) aerosol forcing as at least 1.5–2 W/m 2 , with turning point at 2010, consistent with Fig. 3 of Bauer et al . [ 175 ] GHG plus aerosol forcing grew +0.3 W/m 2 per decade (GHGs: +0.45, aerosols: –0.15) during 1970–2010, which produced warming of 0.18°C per decade. With current policies, we expect climate forcing for a few decades post-2010 to increase 0.5–06 W/m 2 per decade and produce global warming of at least +0.27°C per decade. In that case, global warming will reach 1.5°C in the 2020s and 2°C before 2050 ( Fig. 24 ). Such acceleration is dangerous in a climate system that is already far out of equilibrium and dominated by multiple amplifying feedbacks.

Global temperature relative to 1880–1920. Edges of the predicted post-2010 accelerated warming rate (see text) are 0.36 and 0.27°C per decade.

Global temperature relative to 1880–1920. Edges of the predicted post-2010 accelerated warming rate (see text) are 0.36 and 0.27°C per decade.

The sharp change of ship emissions in 2020 (The great inadvertent aerosol experiment section) provides an indirect measure of aerosol effects. Diamond [ 176 ] finds a cloud brightness decrease of order 1 W/m 2 in a shipping corridor. We find a larger effect, increased absorption of about 3 W/m 2 in regions of heavy ship traffic in the North Atlantic and North Pacific ( Fig. 22 ), but a longer record is needed to define significance. However, the single best sentinel for global climate change is Earth’s energy imbalance.

Earth’s energy imbalance

Earth’s energy imbalance (EEI) is the net gain (or loss) of energy by the planet, the difference between absorbed solar energy and emitted thermal (heat) radiation. As long as EEI is positive, Earth will continue to get hotter. EEI is hard to measure, a small difference between two large quantities (Earth absorbs and emits about 240 W/m 2 averaged over the entire planetary surface), but change of EEI can be well-measured from space [ 81 ]. Absolute calibration is from the change of heat in the heat reservoirs, mainly the global ocean, over a period of at least a decade, as needed to reduce error due to the finite number of places that the ocean is sampled [ 80 ]. EEI varies year-to-year ( Fig. 25 ), largely because global cloud amount varies with weather and ocean dynamics, but averaged over several years EEI helps inform us about what is needed to stabilize climate.

12-month running-mean of Earth’s energy imbalance from CERES satellite data [81] normalized to 0.71 W/m2 mean for July 2005–June 2015 (blue bar) from in situ data [80].

12-month running-mean of Earth’s energy imbalance from CERES satellite data [ 81 ] normalized to 0.71 W/m 2 mean for July 2005–June 2015 (blue bar) from in situ data [ 80 ].

The data indicate that EEI has doubled since the first decade of this century ( Fig. 25 ). This increase is one basis for our prediction of post-2010 acceleration of the global warming rate. The EEI increase may be partly due to restrictions on maritime aerosol precursor emissions imposed in 2015 and 2020 (The great inadvertent aerosol experiment section), but the growth rate of GHG climate forcing also increased in 2015 and since has remained at the higher level (Equilibrium warming versus committed warming section).

Reduction of climate forcing needed to reduce EEI to zero is greater than EEI because of ultrafast cloud feedback (Slow, fast and ultrafast feedbacks section), but the magnitude of this effect is uncertain (SM6). Cloud feedbacks are only beginning to be simulated well, but climate sensitivity near 1.2°C per W/m 2 implies that the net cloud feedback is large and deserves greater attention. Precise monitoring of EEI is essential as a sentinel for future climate change and to assess efforts to stabilize climate and avoid undesirable consequences. Global satellite monitoring of geographical and temporal changes of EEI and ocean in situ monitoring (especially in polar regions of rapid change) are both needed for the sake of understanding ongoing climate change.

Equilibrium warming versus committed warming

Equilibrium warming for today’s climate forcing is the warming required to restore Earth’s energy balance if atmospheric composition is fixed at today’s conditions. Equilibrium warming is a benchmark that can be evaluated from atmospheric composition and paleoclimate data, with little involvement of climate models. It is the standard benchmark used in definition of the Charney ECS (equilibrium climate sensitivity excluding slow feedbacks) [ 4 ] and ESS (Earth system sensitivity, which includes slow feedbacks such as ice sheet size) [ 71 ]. GHG climate forcing now is 4.6 W/m 2 relative to the mid-Holocene (7 kyBP) or 4.1 W/m 2 relative to 1750. There is little merit in debating whether GHG forcing is 4.6 or 4.1 W/m 2 because it is still increasing 0.5 W/m 2 per decade (Perspective on policy implications section). ECS response to 4.6 W/m 2 forcing for climate sensitivity 1.2°C per W/m 2 is 5.5°C. The eventual Earth system response (ESS) to sustained 4.6 W/m 2 forcing is about 10°C (Earth system sensitivity section), because that forcing is large enough to deglaciate Antarctica ( Fig. 23 ). Net human-made forcing today is probably near 3 W/m 2 due to negative aerosol forcing. Even 3 W/m 2 may be sufficient to largely deglaciate Antarctica, if the forcing is left in place permanently ( Fig. 23 ).

‘Committed warming’ is less precisely defined; even in the current IPCC report [ 12 ] (p. 2222) it has multiple definitions. One concept is the warming that occurs if human-made GHG emissions cease today, but that definition is ill-posed as well as unrealistic. Do aerosol emissions also cease? That would cause a sudden leap in Earth’s energy imbalance, a ‘termination shock,’ as the cooling effect of human-made aerosols disappears. A more useful definition is the warming that will occur with plausibly rapid phasedown of GHG emissions, including comparison with ongoing reality. However, the required ‘integrated assessment models,’ while useful, are complex and contain questionable assumptions that can mislead policy (see Perspective on policy implications section).

Nature’s capacity for restoration provides hope that future warming can be limited, if humanity moves promptly toward sustainable energy and climate policies. Earth’s ability to remove human-made CO 2 emissions from the atmosphere is revealed by Fig. 26 . Fossil fuel emissions now total more than 10 GtC/year, which is almost 5 ppm of CO 2 , yet CO 2 in the air is only increasing 2.5 ppm/year. The other half is being taken up by the ocean, solid land, and biosphere. Indeed, Earth is taking up even more because deforestation, fires, and poor agricultural and forestry practices are additional human-made CO 2 sources. If human emissions ceased, atmospheric CO 2 would initially decline a few ppm per year, but uptake would soon slow—it would take millennia for CO 2 to reach preindustrial levels [ 131 ]. This underscores the difficulty of restoring Earth’s energy balance via emission reductions alone. Furthermore, fossil fuels have raised living standards in most of the world and still provide 80% of the world’s energy, which contributes to a policy inertia. As the reality of climate change emerges, the delayed response of climate and amplifying feedbacks assure that the world has already set sail onto even more turbulent climate seas. Scientists must do their best to help the public understand policy options that may preserve and restore a propitious climate for future generations.

Fossil fuel emissions divided into portions appearing in the annual increase of airborne CO2 and the remainder, which is taken up by the ocean and land (1 ppm CO2 ∼ 2.12 GtC).

Fossil fuel emissions divided into portions appearing in the annual increase of airborne CO 2 and the remainder, which is taken up by the ocean and land (1 ppm CO 2  ∼ 2.12 GtC).

This section is the first author’s perspective based on more than 20 years of experience on policy issues that began with a paper [ 179 ] and two workshops [ 180 ] that he organized at the East-West Center in Hawaii, followed by meetings and workshops with utility experts and trips to more than a dozen nations for discussions with government officials, energy experts, and environmentalists. The aim was to find a realistic scenario with a bright energy and climate future, with emphasis on cooperation between the West and nations with emerging or underdeveloped economies.

Energy, CO 2 and the climate threat

The world’s energy and climate path has good reason: fossil fuels powered the industrial revolution and raised living standards. Fossil fuels still provide most of the world’s energy ( Fig. 27a ) and produce most CO 2 emissions ( Fig. 27b ). Much of the world is still in early or middle stages of economic development. Energy is needed and fossil fuels are a convenient, affordable source of energy. One gallon (3.8 l) of gasoline (petrol) provides the work equivalent of more than 400 h labor by a healthy adult. These benefits are the basic reason for continued high emissions. The Covid pandemic dented emissions in 2020, but 2022 global emissions were a record high level. Fossil fuel emissions from mature economies are beginning to fall due to increasing energy efficiency, introduction of carbon-free energies, and export of manufacturing from mature economies to emerging economies. However, at least so far, those reductions have been more than offset by increasing emissions in developing nations ( Fig. 28 ).

Global energy consumption and CO2 emissions (Hefner at al. [177] and Energy Institute [178]).

Global energy consumption and CO 2 emissions (Hefner at al . [ 177 ] and Energy Institute [ 178 ]).

Fossil fuel CO2 emissions from mature and emerging economies. China is counted as an emerging economy. Data sources as in Fig. 27.

Fossil fuel CO 2 emissions from mature and emerging economies. China is counted as an emerging economy. Data sources as in Fig. 27 .

The potential for rising CO 2 to be a serious threat to humanity was the reason for the 1979 Charney report, which confirmed that climate was likely sensitive to expected CO 2 levels in the 21st century. In the 1980s it emerged that high climate sensitivity implied a long delay between changing atmospheric composition and the full climate response. Ice core data revealed the importance of amplifying climate feedbacks. A climate characterized by delayed response and amplifying feedbacks is especially dangerous because the public and policymakers are unlikely to make fundamental changes in world energy systems until they see visible evidence of the threat. Thus, it is incumbent on scientists to make this situation clear to the public as soon as possible. That task is complicated by the phenomenon of scientific reticence.

Scientific reticence

Bernard Barber decried the absence of attention to scientific reticence, a tendency of scientists to resist scientific discovery or new ideas [ 139 ]. Richard Feynman needled fellow physicists about their reticence to challenge authority [ 181 ], specifically to correct the electron charge that Millikan derived in his famous oil drop experiment. Later researchers moved Millikan’s result bit by bit—experimental uncertainties allow judgment—reaching an accurate result only after years. Their reticence embarrassed the physics community but caused no harm to society. A factor that may contribute to reticence among climate scientists is ‘delay discounting:’ preference for immediate over delayed rewards [ 182 ]. The penalty for ‘crying wolf’ is immediate, while the danger of being blamed for ‘fiddling while Rome was burning’ is distant. One of us has noted [ 183 ] that larding of papers and proposals with caveats and uncertainties increases chances of obtaining research support. ‘Gradualism’ that results from reticence is comfortable and well-suited for maintaining long-term support. Gradualism is apparent in IPCC’s history in evaluating climate sensitivity as summarized in our present paper. Barber identifies professional specialization—which causes ‘outsiders’ to be ignored by ‘insiders’—as one cause of reticence; specialization is relevant to ocean and ice sheet dynamics, matters upon which the future of young people hangs.

Discussion [ 184 ] with field glaciologists 13 20 years ago revealed frustration with IPCC’s ice sheet assessment. One glaciologist said—about a photo [ 185 ] of a moulin (a vertical shaft that carries meltwater to the base of the Greenland ice sheet)—‘the whole ice sheet is going down that damned hole!’ Concern was based on observed ice sheet changes and paleoclimate evidence of sea level rise by several meters in a century, implying that ice sheet collapse is an exponential process. Thus, as an alternative to ice sheet models, we carried out a study described in Ice Melt [ 13 ]. In a GCM simulation, we added a growing freshwater flux to the ocean surface mixed layer around Greenland and Antarctica, with the flux in the early 21st century based on estimates from in situ glaciological studies [ 186 ] and satellite data on sea level trends near Antarctica [ 187 ]. Doubling times of 10 and 20 years were used for the growth of freshwater flux. One merit of our GCM was reduced, more realistic, small-scale ocean mixing, with a result that Antarctic Bottom Water formed close to the Antarctic coast [ 13 ], as in the real world. Growth of meltwater and GHG emissions led to shutdown of the North Atlantic and Southern Ocean overturning circulations, amplified warming at the foot of the ice shelves that buttress the ice sheets, and other feedbacks consistent with ‘nonlinearly growing sea level rise, reaching several meters in 50–150 years’ [ 13 ]. Shutdown of ocean overturning circulation occurs this century, as early as midcentury. The 50–150-year time scale for multimeter sea level rise is consistent with the 10–20-year range for ice melt doubling time. Real-world ice melt will not follow a smooth curve, but its growth rate is likely to accelerate in coming years due to increasing heat flux into the ocean ( Fig. 25 ).

We submitted Ice Melt to a journal that makes reviews publicly available [ 188 ]. One reviewer, an IPCC lead author, seemed intent on blocking publication, while the other reviewer described the paper as a ‘masterwork of scholarly synthesis, modeling virtuosity, and insight, with profound implications’. Thus, the editor obtained additional reviewers, who recommended publication. Promptly, an indictment was published [ 189 ] of our conclusion that continued high GHG emissions would cause shutdown of the AMOC (Atlantic Meridional Overturning Circulation) this century. The 15 authors, representing leading GCM groups, used 21 climate projections from eight ‘…state-of-the-science, IPCC class…’ GCMs to conclude that ‘…the probability of an AMOC collapse is negligible. This is contrary to a recent modeling study [ Hansen et al . , 2016 ] that used a much larger, and in our assessment unrealistic, Northern Hemisphere freshwater forcing… According to our probabilistic assessment, the likelihood of an AMOC collapse remains very small (<1% probability) if global warming is below ∼ 5K…’[ 189 ]. They treated the ensemble of their model results as if it were the probability distribution for the real world.

In contrast, we used paleoclimate evidence, global modeling, and ongoing climate observations. Paleoclimate data [ 190 ] showed that AMOC shutdown is not unusual and occurred in the Eemian (when global temperature was similar to today), and also that sea level in the Eemian rose a few meters within a century [ 191 ] with the likely source being collapse of the West Antarctic ice sheet. Although we would not assert that our model corrected all excessive ocean mixing, the higher vertical resolution and improved mixing increased the sensitivity to freshwater flux, as confirmed in later tests [ 192 ]. Modern observations showed and continue to add evidence that the overturning Southern Ocean [ 193 , 194 ] and North Atlantic [ 195 ] are already slowing. Growth of meltwater injection onto the Southern [ 196 ] and North Atlantic Oceans [ 197 ] is consistent with a doubling time of 10–20 years. High climate sensitivity inferred in our present paper also implies there will be a greater increase of precipitation on polar oceans than that in most climate models.

The indictment of Ice Melt by Bakker et al . [ 189 ] was accepted by the research community. Papers on the same topics ignored our paper or referred to it parenthetically with a note that we used unrealistic melt rates, even though these were based on observations. Ice Melt was blackballed in IPCC’s AR6 report, which is a form of censorship [ 14 ]. Science usually acknowledges alternative views and grants ultimate authority to nature. In the opinion of our first author, IPCC does not want its authority challenged and is comfortable with gradualism. Caution has merits, but the delayed response and amplifying feedbacks of climate make excessive reticence a danger. Our present paper—via revelation that the equilibrium response to current atmospheric composition is a nearly ice-free Antarctica—amplifies concern about locking in nonlinearly growing sea level rise. Also, our conclusion that CO 2 was about 450 ppm at Antarctic glaciation disparages ice sheet models. Portions of the ice sheets may be recalcitrant to rapid change, but enough ice is in contact with the ocean to provide of the order of 25 m (80 feet) of sea level rise. Thus, if we allow a few meters of sea level rise, we may lock in much larger sea level rise.

Climate change responsibilities

The industrial revolution began in the U.K., which was the largest source of fossil fuel emissions in the 19th century ( Fig. 29a ), but development soon moved to Germany, the rest of Europe, and the U.S. Nearly half of global emissions were from the U.S. in the early 20th century, and the U.S. is presently the largest source of cumulative emissions ( Fig. 29b ) that drive climate change [ 198 , 199 ]. Mature economies, mainly in the West, are responsible for most cumulative emissions, especially on a per capita basis ( Fig. 30 ). Growth of emissions is now occurring in emerging economies ( Figs 28 and 29a ). China’s cumulative emissions will eventually pass those of the U.S. in the absence of a successful effort to replace coal with carbon-free energy.

Fossil fuel CO2 emissions by nation or region as a fraction of global emissions. Data sources as in Fig. 27.

Fossil fuel CO 2 emissions by nation or region as a fraction of global emissions. Data sources as in Fig. 27 .

Cumulative per capita national fossil fuel emissions [200].

Cumulative per capita national fossil fuel emissions [ 200 ].

Greenhouse gas emissions situation

The United Nations uses a target for maximum global warming to cajole progress in limiting climate change. The 2015 Paris Agreement [ 201 ] aimed to hold ‘the increase in the global average temperature to well below 2°C above the pre-industrial levels and pursue efforts to limit the temperature increase to 1.5°C above the pre-industrial levels.’ The IPCC AR5 report added a climate forcing scenario, RCP2.6, with a rapid decrease of GHG climate forcings, as needed to prevent global warming from exceeding 2°C. Since then, a gap between that scenario and reality opened and is growing ( Fig. 31 ). The 0.03 W/m 2 gap in 2022 could be closed by extracting CO 2 from the air. However, required negative emissions (CO 2 extracted from the air and stored permanently) must be larger than the desired atmospheric CO 2 reduction by a factor of about 1.7 [ 63 ]. Thus, the required CO 2 extraction is 2.1 ppm, which is 7.6 GtC. Based on a pilot direct-air carbon capture plant, Keith [ 202 ] estimates an extraction cost of $450–920 per tC, as clarified elsewhere [ 203 ]. Keith’s cost range yields an extraction cost of $3.4–7.0 trillion. That covers excess emissions in 2022 only; it is an annual cost. Given the difficulty the UN faced in raising $0.1 trillion for climate purposes and the growing emissions gap ( Fig. 31 ), this example shows the need to reduce emissions as rapidly as practical and shows that carbon capture cannot be viewed as the solution, although it may play a role in a portfolio of policies, if its cost is driven down.

Annual growth of climate forcing by GHGs [38] including part of O3 forcing not included in CH4 forcing (Supplementary Material). MPTG and OTG are Montreal Protocol and Other Trace Gases.

Annual growth of climate forcing by GHGs [ 38 ] including part of O 3 forcing not included in CH 4 forcing ( Supplementary Material ). MPTG and OTG are Montreal Protocol and Other Trace Gases.

IPCC (Intergovernmental Panel on Climate Change), the scientific body advising the world on climate, has not bluntly informed the world that the present precatory policy approach will not keep warming below 1.5°C or even 2°C. The ‘tragedy of the commons’ [ 204 ] is that, as long as fossil fuel pollution can be dumped in the air free of charge, agreements such as the Kyoto Protocol [ 205 ] and Paris Agreement have limited effect on global emissions. Political leaders profess ambitions for dubious net-zero emissions while fossil fuel extraction expands. IPCC scenarios that phase down human-made climate change amount to ‘a miracle will occur’. The IPCC scenario that moves rapidly to negative global emissions (RCP2.6) has vast biomass-burning powerplants that capture and sequester CO 2 , a nature-ravaging, food-security-threatening [ 206 ], proposition without scientific and engineering credibility and without a realistic chance of being deployed at scale and on time to address the climate threat.

Climate and energy policy

Climate science reveals the threat of being too late. ‘Being too late’ refers not only to warning of the climate threat, but also to technical advice on policy implications. Are we scientists not complicit if we allow reticence and comfort to obfuscate our description of the climate situation? Does our training, years of graduate study and decades of experience, not make us well-equipped to advise the public on the climate situation and its policy implications? As professionals with deep understanding of planetary change and as guardians of young people and their future, do we not have an obligation, analogous to the code of ethics of medical professionals, to render to the public our full and unencumbered diagnosis? That is our objective.

The basis for the following opinions of the first author, to the extent not covered in this paper, will be described in a book in preparation [ 2 ]. We are in the early phase of a climate emergency. The present huge planetary energy imbalance assures that climate will become less tolerable to humanity, with greater climate extremes, before it is feasible to reverse the trend. Reversing the trend is essential—we must cool the planet—for the sake of preserving shorelines and saving the world’s coastal cities. Cooling will also address other major problems caused by global warming. We should aim to return to a climate like that in which civilization developed, in which the nature that we know and love thrived. As far as is known, it is still feasible to do that without passing through irreversible disasters such as many-meter sea level rise.

Abundant, affordable, carbon-free energy is essential to achieve a world with propitious climate, while recognizing the rights and aspirations of all people. The staggering magnitude of the task is implied by global and national carbon intensities: carbon emissions per unit energy use ( Fig. 32 ). Global carbon intensity must decline to near zero over the next several decades. This chart—not vaporous promises of net zero future carbon emissions inserted in integrated assessment models—should guide realistic assessment of progress toward clean energy. Policy must include apolitical targeting of support for development of low-cost carbon-free energy. All nations would do well to study strategic decisions of Sweden, which led past decarbonization efforts ( Fig. 32 ) and is likely to lead in the quest for zero or negative carbon intensity that will be needed to achieve a bright future for today’s young people and future generations.

Carbon intensity (carbon emissions per unit energy use) of several nations and the world. Mtoe = megatons of oil equivalent. Data sources as in Fig. 27.

Carbon intensity (carbon emissions per unit energy use) of several nations and the world. Mtoe = megatons of oil equivalent. Data sources as in Fig. 27 .

Given the global situation that we have allowed to develop, three actions are now essential.

First, underlying economic incentives must be installed globally to promote clean energy and discourage CO 2 emissions. Thus, a rising price on GHG emissions is needed, enforced by border duties on products from nations without a carbon fee. Public buy-in and maximum efficacy require the funds to be distributed to the public, which will also address wealth disparity. Economists in the U.S. support carbon fee-and-dividend [ 207 ]; college and high school students join in advocacy [ 208 ]. A rising carbon price creates a level playing field for energy efficiency, renewable energy, nuclear power, and innovations; it would spur the thousands of ‘miracles’ needed for energy transition. However, instead, fossil fuels and renewable energy are now subsidized. Thus, nuclear energy has been disadvantaged and excluded as a ‘clean development mechanism’ under the Kyoto Protocol, based on myths about nuclear energy unsupported by scientific fact [ 209 ]. A rising carbon price is crucial for decarbonization, but not enough. Long-term planning is needed. Sweden provides an example: 50 years ago, its government decided to replace fossil fuel power stations with nuclear energy, which led to its extraordinary and rapid decarbonization ( Fig. 32 ).

Second, global cooperation is needed. De facto cooperation between the West and China drove down the price of renewable energy. Without greater cooperation, developing nations will be the main source of future GHG emissions ( Fig. 28 ). Carbon-free, dispatchable electricity is a crucial need. Nations with emerging economies are eager to have modern nuclear power because of its small environmental footprint. China-U.S. cooperation to develop low-cost nuclear power was proposed, but stymied by U.S. prohibition of technology transfer [ 210 ]. Competition is normal, but it can be managed if there is a will, reaping benefits of cooperation over confrontation [ 211 ]. Of late, priority has been given instead to economic and military hegemony, despite recognition of the climate threat, and without consultation with young people or seeming consideration of their aspirations. Scientists can support an ecumenical perspective of our shared future by expanding international cooperation. Awareness of the gathering climate storm will grow this decade, so we must increase scientific understanding worldwide as needed for climate restoration.

Third, we must take action to reduce and reverse Earth’s energy imbalance. Highest priority is to phase down emissions, but it is no longer feasible to rapidly restore energy balance via only GHG emission reductions. Additional action is almost surely needed to prevent grievous escalation of climate impacts including lock-in of sea level rise that could destroy coastal cities world-wide. At least several years will be needed to define and gain acceptance of an approach for climate restoration. This effort should not deter action on mitigation of emissions; on the contrary, the concept of human intervention in climate is distasteful to many people, so support for GHG emission reductions will likely increase. Temporary solar radiation management (SRM) will probably be needed, e.g. via purposeful injection of atmospheric aerosols. Risks of such intervention must be defined, as well as risks of no intervention; thus, the U.S. National Academy of Sciences recommends research on SRM [ 212 ]. The Mt. Pinatubo eruption of 1991 is a natural experiment [ 213 , 214 ] with a forcing that reached [ 30 ] –3 W/m 2 . Pinatubo deserves a coordinated study with current models. The most innocuous aerosols may be fine salty droplets extracted from the ocean and sprayed into the air by autonomous sailboats [ 215 ]. This approach has been discussed for potential use on a global scale [ 216 ], but it needs research into potential unintended effects [ 217 ]. This decade may be our last chance to develop the knowledge, technical capability, and political will for actions needed to save global coastal regions from long-term inundation.

Politics and climate change

Actions needed to drive carbon intensity to zero—most important a rising carbon fee—are feasible, but not happening. The first author gained perspective on the reasons why during trips to Washington, DC, and to other nations at the invitation of governments, environmentalists, and, in one case, oil executives in London. Politicians from right (conservative) and left (progressive) parties are affected by fossil fuel interests. The right denies that fossil fuels cause climate change or says that the effect is exaggerated. The left takes up the climate cause but proposes actions with only modest effect, such as cap-and-trade with offsets, including giveaways to the fossil fuel industry. The left also points to work of Amory Lovins as showing that energy efficiency plus renewables (mainly wind and solar energy) are sufficient to phase out fossil fuels. Lovins says that nuclear power is not needed. It is no wonder that the President of Shell Oil would write a foreword with praise for Lovins’ book, Reinventing Fire [ 218 ], and that the oil executives in London did not see Lovins’ work as a threat to their business.

Opportunities for progress often occur in conjunction with crises. Today, the world faces a crisis—political polarization, especially in the United States—that threatens effective governance. Yet the crisis offers an opportunity for young people to help shape the future of the nation and the planet. Ideals professed by the United States at the end of World War II were consummated in formation of the United Nations, the World Bank, the Marshall Plan, and the Universal Declaration of Human Rights. Progress toward equal rights continued, albeit slowly. The ‘American dream’ of economic opportunity was real, as most people willing to work hard could afford college. Immigration policy welcomed the brightest; NASA in the 1960s invited scientists from European countries, Japan, China, India, Canada, and those wanting to stay found immigration to be straightforward. But the power of special interests in Washington grew, government became insular and inefficient, and Congress refused to police itself. Their first priority became reelection and maintenance of elite status, supported by special interests. Thousands of pages of giveaways to special interests lard every funding bill, including the climate bill titled ‘Inflation Reduction Act’—Orwellian double-speak—as the funding is borrowed from young people via deficit spending. The public is fed up with the Washington swamp but hamstrung by rigid two-party elections focused on a polarized cultural war.

A political party that takes no money from special interests is essential to address political polarization, which is necessary if the West is to be capable of helping preserve the planet and a bright future for coming generations. Young people showed their ability to drive an election—via their support of Barack Obama in 2008 and Bernie Sanders in 2016—without any funding from special interests. Groundwork is being laid to allow third party candidates in 2026 and 2028 elections in the U.S. Ranked voting is being advocated in every state to avoid the ‘spoiler’ effect of a third party. It is asking a lot to expect young people to grasp the situation that they have been handed—but a lot is at stake. As they realize that they are being handed a planet in decline, the first reaction may be to stamp their feet and demand that governments do better, but that has little effect. Nor is it sufficient to parrot big environmental organizations, which are now part of the problem, as they are partly supported by the fossil fuel industry and wealthy donors who are comfortable with the status quo. Instead, young people have the opportunity to provide the drive for a revolutionary third party that restores democratic ideals while developing the technical knowledge that is needed to navigate the stormy sea that their world is setting out upon.

We thank Eelco Rohling for inviting JEH to describe our perspective on global climate response to human-made forcing. JEH began to write a review of past work, but a paper on the LGM by Jessica Tierney et al . [ 49 ] and data on changing ship emissions provided by Leon Simons led to the need for new analyses and division of the paper into two parts. We thank Jessica also for helpful advice on other related research papers, Jim Zachos and Thomas Westerhold for explanations of their data and interpretations, Ed Dlugokencky of the NOAA Earth System Research Laboratory for continually updated GHG data, and David Arthur for pointing out the paper by Steinberger et al . JEH designed the study and carried out the research with help of Makiko Sato and Isabelle Sangha; Larissa Nazarenko provided data from GISS models and helped with analysis; Leon Simons provided ship emission information and aided interpretations; Pushker Kharecha provided critical review of the paper; James Zachos provided critical interpretation of ocean core data needed for interpretation of Cenozoic climate; Norman Loeb and Karina von Schuckmann provided EEI data and insight about implications; Matthew Osman provided paleoclimate data and an insightful review of an early draft paper; Qinjian Jin provided simulations of atmospheric sulfate and interpretations; Eunbi Jeong reviewed multiple drafts and advised on presentation; all authors contributed to our research summarized in the paper and reviewed and commented on the manuscript. Climate Science, Awareness and Solutions, which is directed by JEH and supports MS and PK is a 501(C3) nonprofit supported 100% by public donations. Principal supporters in the past few years have been the Grantham Foundation, Frank Batten, Eric Lemelson, James and Krisann Miller, Carl Page, Peter Joseph, Ian Cumming, Gary and Claire Russell, Donald and Jeanne Keith Ferris, Aleksandar Totic, Chris Arndt, Jeffrey Miller, Morris Bradley and about 150 more contributors to annual appeals.

Supplementary data are available at Oxford Open Climate Change online.

The authors declare that they have no conflict of interest.

The data used to create the Figs in this paper are available in the Zenodo repository, at https://zenodo.org/record/8419583 .

James Hansen (Conceptualization [lead], Data curation [equal], Formal analysis [lead], Funding acquisition [lead], Investigation [lead], Methodology [lead], Project administration [lead], Resources [lead], Software [equal], Supervision [lead], Validation [lead], Visualization [equal], Writing—original draft [lead], Writing—review and editing [lead]), Makiko Sato (Data curation [equal], Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Project administration [supporting], Resources [supporting], Software [equal], Supervision [supporting], Validation [supporting], Visualization [equal], Writing—original draft [supporting], Writing—review and editing [supporting]), Leon Simons (Data curation [supporting], Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Visualization [supporting], Writing—review and editing [supporting]), Larissa S. Nazarenko (Data curation [supporting], Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Visualization [supporting], Writing—review and editing [supporting]), Isabelle Sangha (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Pushker Kharecha (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), James Zachos (Data curation [supporting], Resources [supporting], Writing—review and editing [supporting]), Karina von Schuckmann (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Norman G. Loeb (Data curation [supporting], Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Visualization [supporting], Writing—review and editing [supporting]), Matthew B. Osman (Data curation [supporting], Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Visualization [supporting], Writing—review and editing [supporting)], Qinjian Jin (Data curation [supporting], Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Visualization [supporting], Writing—review and editing [supporting]), George Tselioudis (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Writing—review and editing [supporting]), Eunbi Jeong (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Andrew Lacis (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Reto Ruedy (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Gary Russell (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Junji Cao (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]), Jing Li (Formal analysis [supporting], Investigation [supporting], Methodology [supporting], Resources [supporting], Software [supporting], Supervision [supporting], Validation [supporting], Writing—review and editing [supporting]).

Drafts of the chapters of Sophie’s Planet relevant to climate sensitivity are available here ; criticisms are welcome.

David EE, Jr later became a global warming denier.

GISS (2020) model is described as GISS-E2.1-G-NINT in published papers; NINT (noninteractive) signifies that the models use specified GHG and aerosol amounts.

An imbalance of 1 W/m 2 for a millennium is enough energy to melt ice raising sea level 110 m or to raise the temperature of the ocean’s upper kilometer by 11°C.

Tom Delworth (NOAA Geophysical Fluid Dynamics Laboratory), Gokhan Danabasoglu (National Center for Atmospheric Research), and Jonathan Gregory (UK Hadley Centre) kindly provided long 2 × CO 2 runs of GCMs of these leading modeling groups. All three models had response time as slow or slower than the GISS GCM.

The GISS (2014) model is labeled as GISS-E2-R-NINT and GISS (2020) as GISS-E2.1-G-NINT in published papers, where NINT (noninteractive) signifies that the models use specified GHG and aerosol amounts.

In Swedish, trapps are stairs. Basalt formations are commonly in layers from multiple extrusions.

Small apparent discrepancy is roundoff. CO 2 forcing is 9.13 W/m 2 and solar forcing is −1.16 W/m 2 at 50 MyBP.

Forcing = 4.6 W/m 2 assumes that the increase of non-CO 2 GHGs is human-made. This is true for CFCs and most trace gases, but a small part of CH 4 and N 2 O growth could be a slow feedback, slightly reducing the GHG forcing.

9.9°C for ECS = 1.2°C per W/m 2 ; 10.1°C for ECS = 1.22°C per W/m 2 (the precise ECS for 7°C LGM cooling).

Two significant flaws in the derivation of this ‘alternative aerosol scenario’ were largely offsetting: (1) the intermediate climate response function employed was too ‘fast’, but (2) this was compensated by use of a low climate sensitivity of 3°C for 2 × CO 2 .

In the absence of a response function from a GCM with ECS = 4°C, we use the normalized response function of the GISS (2020) model and put λ = 1°C per W/m 2 in Equation (5) .

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Essays on Climate Change

With global warming being a growing problem that affects our atmosphere, you can find research paper topics in climate changing that will offer useful information to readers. When covering topics like this, it is essential to include the effects and problems being caused within our ecosystem. From greenhouse gas emissions to increased levels of ... dioxide, sample essays can provide a wealth of information to use when creating an outline. College essays about climate change for college students include the latest research and statistics that can be used to write about how this is affecting the entire planet. Argumentative essay examples on climate change will provide tips for developing your introduction and factual information to use in a conclusion.

How to Prevent Climate Change

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Ecological Collapse: Causes and Solutions

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Causes of Climate Change

Climate change is an ongoing issue in the world today. There are studies and facts that show what climate change is and how badly the Earth and its many organisms and environments are being affected. There are many different known causes of climate change, the main factors being greenhouse gases, humans, and the Sun. The effects of these causes include changes in the temperature of the Earth, in frequency and strength of natural disasters, and in many species and habitats […]

On Global Warming and Climate Change

I believe that among the numerous critical issues facing most Americans in this world today, climate change stands as one of, if not the most urgent. However, understanding and assimilating the different causes of the ever-growing environmental problems critically facing our lives today are crucial for reducing our pollution footprint. Climate change effects include major changes in temperature, precipitation, wind patterns, as well as other frequent disastrous weather phenomenon. That said, climate change policy in the US has transformed timidly […]

Deforestation as a Cause of Climate Change

The research question that has been pondering for quite a while is “does deforestation lead to climate change through its mediating attributes of mean ambient temperatures as evidenced by modern geospatial technologies?” This question is vital to all professional environmental sources and their methods as it evaluates the effect of modern techniques at detecting the links between dependent and outcome variables in the issue of climate change and vegetation cover. The use of modern technologies to ascertain the extent of […]

Effects of Climate Change on Ursus Maritimus

Polar bears are the mystic creatures residing in the northern apex of the world, they are one of the few animal that currently live with the least human encroachment. There are estimated about 25,000-31,000 number of Polar Bears alive today divided into 19 subpopulations (Rode, K. D., Robbins, C. T., Nelson, L., & Amstrup, S. C. 2015). The Arctic circle is one of the most delicate ecosystems on the planet, and because of fragile nature of the ecosystem (McConnell., et […]

The Effects of Globalization on Air Pollution in China’s Largest Cities

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Climate Change Example Water

It’s a natural resource for mostly everything that needs to survive or use for hygiene. Time passes and us humans have used water over a billion of years and as that time passes, the earth and climate changes. Let’s time travel to the future. Humans now use water to wash things in these loud machines called washers. These washers use 15 to 20 gallons of water per day for one load of clothes, while back then, people used rivers to […]

The Global Health Threat of Climate Change

Climate change is the biggest global health threat of the 21st century. Effects of climate change on health will affect most populations in the next decades and put the lives and wellbeing of billions of people at increased risk. During this century, earth’s average surface temperature rises are likely to exceed the safe threshold of 2°C above preindustrial average temperature. Rises will be greater at higher latitudes, with medium-risk scenarios predicting 2-3°C rises by 2090 and 4-5°C rises in northern […]

Is Global Warming Myth or Reality

It’s a common misconception that global warming is the physical warming of the globe everywhere, resulting in warmer weather all the time. Statements like “how can the earth be in global warming if this is one of the coldest winters in the last three years.” Or, “but I can still make a snowman!”. Or, the recent tweet from President Trump, “In the beautiful midwest windshield temperatures are reaching minus 60 degrees. What the hell is going on with Global Warming? […]

Is Global Warming Skepticism Just Smoke and Mirrors

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What is Climate Change

By the end of the 21st Century, scientists project that the average global temperature will rise between 3.2 and 7.2 degrees fahrenheit. This may not seem like a ton, but you will be surprised at how much a degree or two can affect our little world. It will not only affect us as humans, but it will and already has ruined the lives of some animals. Climate change is mostly caused by humans and the way that our atmosphere is […]

Pollution and Climate Change

Climate change and contamination are two extremely important controversial topics not only for the United States and China but for the entire world. In the Ted talk “How China is (and isn’t) fighting pollution and climate change”, Angel Hsu discusses the importance of renewable energy. I believe her purpose is to show the world how much China has improved in such a short amount of time, but to also warn us that there is still so much that has to […]

Polar Bears and Climate Change

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The last several decades humans have spent on Earth will leave a mark beyond artifacts and history. We will leave a measurable footprint that tells a story of not only the conditions we lived in, but also the carelessness of our actions. Eric Sanderson, an associate director in the Landscape Ecology and Geographic Analysis Program at the Wildlife Conservation Society Institute, defines the human footprint as a quantitative measure of humanity’s impact on earth (892). Our footprint will be one […]

Modelling and Analysis of Climate Change

1. Executive Summary The burning topic throughout the world is “Climate Change”?. The close linkage between economic growth of the country and Greenhouse gas emission is indeed a serious debate. Development in industrial sectors will naturally increase GDP accompanied by emissions. However increase in GDP will pay way for higher standard of lifestyle and more income which results in increased consumption of energy and hence more emissions. The alarming global warming and the pressures of international treaties to reduce the […]

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When I first hear the words Nuclear Energy or Nuclear Power I immediately think of bombs, weapons, radiation, and danger. I associate the word nuclear with a negative connotation and a sense of fear. In school, I had learned about the war and how the United States had used nuclear weapons to bomb other countries to prevail to victory. However, this was all I had learned regarding this vast, complex topic of nuclear power. I now realize that nuclear energy […]

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Industrialization side-effect Industrialization is advanced by energy utilization of coal, oil and gaseous petrol. A long period of time back, non-renewable energy sources were framed by decay and pressing factor of verdure. Petrol is the most generally utilized fuel as a crude material for gas creation and as an item. Tainting is an adjustment of the environment that antagonistically influences the daily routine and strength of experiencing things.  Proof of human impact on the environment shows up in every day […]

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Despite the provisional solutions initiated in order to solve environmental matters, indelible consequences linger and will impair the health of civilians presently and in the future. As time progresses and the effects become more prevalent, one may question ways in which pollution can be reduced to limit its impact on public health. In the future, physicians, epidemiologists (those who study disease within a population), and exposure scientists (those who study synthetic, natural, and biological agents in the environment), must collaborate […]

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Introduction Tourism is considered an important sector, especially for the development of the global economy; it contributes to global income creation and the generation of jobs. This is acknowledged by Cooper (2016, p. 5), who states that “tourism is an activity of global importance and significance and a major force in the economy of the world.” Furthermore, the World Travel & Tourism Council’s (WTTC) 2019 research revealed that the travel and tourism sector “accounted for 10.4% of global GDP ($8.8 […]

Research Paper FAQ

What climate change means.

Climate change refers to the transformation of Earth’s weather, regarded as various changes in the usual planet’s climate, such as wind, participation, and temperature. Various human activities cause the change.

What climate change causes?

Climate change brings along various issues such as extreme weather events, heat, floods, and more. In years ahead, things such as an increase in waterborne diseases, diseases transmitted by rodents and insects, poor quality of air, more heat stress are expected to enter the scene.

Why is climate change important?

Climate change became one of the world’s most significant issues. The main reason for that is that human health is vulnerable to all the changes in weather and climate. Extreme weather events and other issues that are expected in the future point out how serious the problem is.

Will climate change ever stop?

Climate change is something that can’t be stopped in a blink of an eye. It is too complex, and it requires a lot of effort, work, and persistence. However, if society stops emitting the greenhouse gases that are causing all the damage, significant improvements would be visible in a few years.

How climate change affects business?

Climate change affects businesses in various ways. Extreme weather various events such as fires, floods, hurricanes, tornadoes, etc., have a direct impact on every global economic sector. All kinds of issues may arise, from labor challenges, increased costs of insurance, and disturbed supply chains.

academic essay on climate change

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Essay on Global Warming

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  • Updated on  
  • Oct 26, 2023

essay on global warming

Being able to write an essay is an integral part of mastering any language. Essays form an integral part of many academic and scholastic exams like the SAT , and UPSC amongst many others. It is a crucial evaluative part of English proficiency tests as well like IELTS , TOEFL , etc. Major essays are meant to emphasize public issues of concern that can have significant consequences on the world. To understand the concept of Global Warming and its causes and effects, we must first examine the many factors that influence the planet’s temperature and what this implies for the world’s future. Here’s an unbiased look at the essay on Global Warming and other essential related topics.

academic essay on climate change

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Since the industrial and scientific revolutions, Earth’s resources have been gradually depleted. Furthermore, the start of the world’s population’s exponential expansion is particularly hard on the environment. Simply put, as the population’s need for consumption grows, so does the use of natural resources , as well as the waste generated by that consumption.

Climate change has been one of the most significant long-term consequences of this. Climate change is more than just the rise or fall of global temperatures; it also affects rain cycles, wind patterns, cyclone frequencies, sea levels, and other factors. It has an impact on all major life groupings on the planet.

Also Read: World Population Day

What is Global Warming?

Global warming is the unusually rapid increase in Earth’s average surface temperature over the past century, primarily due to the greenhouse gases released by people burning fossil fuels . The greenhouse gases consist of methane, nitrous oxide, ozone, carbon dioxide, water vapour, and chlorofluorocarbons. The weather prediction has been becoming more complex with every passing year, with seasons more indistinguishable, and the general temperatures hotter. The number of hurricanes, cyclones, droughts, floods, etc., has risen steadily since the onset of the 21st century. The supervillain behind all these changes is Global Warming. The name is quite self-explanatory; it means the rise in the temperature of the Earth.

Also Read: What is a Natural Disaster?

According to recent studies, many scientists believe the following are the primary four causes of global warming:

  • Deforestation 
  • Greenhouse emissions
  • Carbon emissions per capita

Extreme global warming is causing natural disasters , which can be seen all around us. One of the causes of global warming is the extreme release of greenhouse gases that become trapped on the earth’s surface, causing the temperature to rise. Similarly, volcanoes contribute to global warming by spewing excessive CO2 into the atmosphere.

The increase in population is one of the major causes of Global Warming. This increase in population also leads to increased air pollution . Automobiles emit a lot of CO2, which remains in the atmosphere. This increase in population is also causing deforestation, which contributes to global warming.

The earth’s surface emits energy into the atmosphere in the form of heat, keeping the balance with the incoming energy. Global warming depletes the ozone layer, bringing about the end of the world. There is a clear indication that increased global warming will result in the extinction of all life on Earth’s surface.

Also Read: Land, Soil, Water, Natural Vegetation, and Wildlife Resources

Of course, industries and multinational conglomerates emit more carbon than the average citizen. Nonetheless, activism and community effort are the only viable ways to slow the worsening effects of global warming. Furthermore, at the state or government level, world leaders must develop concrete plans and step-by-step programmes to ensure that no further harm is done to the environment in general.

Although we are almost too late to slow the rate of global warming, finding the right solution is critical. Everyone, from individuals to governments, must work together to find a solution to Global Warming. Some of the factors to consider are pollution control, population growth, and the use of natural resources.

One very important contribution you can make is to reduce your use of plastic. Plastic is the primary cause of global warming, and recycling it takes years. Another factor to consider is deforestation, which will aid in the control of global warming. More tree planting should be encouraged to green the environment. Certain rules should also govern industrialization. Building industries in green zones that affect plants and species should be prohibited.

Also Read: Essay on Pollution

Global warming is a real problem that many people want to disprove to gain political advantage. However, as global citizens, we must ensure that only the truth is presented in the media.

This decade has seen a significant impact from global warming. The two most common phenomena observed are glacier retreat and arctic shrinkage. Glaciers are rapidly melting. These are clear manifestations of climate change.

Another significant effect of global warming is the rise in sea level. Flooding is occurring in low-lying areas as a result of sea-level rise. Many countries have experienced extreme weather conditions. Every year, we have unusually heavy rain, extreme heat and cold, wildfires, and other natural disasters.

Similarly, as global warming continues, marine life is being severely impacted. This is causing the extinction of marine species as well as other problems. Furthermore, changes are expected in coral reefs, which will face extinction in the coming years. These effects will intensify in the coming years, effectively halting species expansion. Furthermore, humans will eventually feel the negative effects of Global Warming.

Also Read: Concept of Sustainable Development

Sample Essays on Global Warming

Here are some sample essays on Global Warming:

Global Warming is caused by the increase of carbon dioxide levels in the earth’s atmosphere and is a result of human activities that have been causing harm to our environment for the past few centuries now. Global Warming is something that can’t be ignored and steps have to be taken to tackle the situation globally. The average temperature is constantly rising by 1.5 degrees Celsius over the last few years. The best method to prevent future damage to the earth, cutting down more forests should be banned and Afforestation should be encouraged. Start by planting trees near your homes and offices, participate in events, and teach the importance of planting trees. It is impossible to undo the damage but it is possible to stop further harm.

Also Read: Social Forestry

Over a long period, it is observed that the temperature of the earth is increasing. This affected wildlife , animals, humans, and every living organism on earth. Glaciers have been melting, and many countries have started water shortages, flooding, and erosion and all this is because of global warming. No one can be blamed for global warming except for humans. Human activities such as gases released from power plants, transportation, and deforestation have increased gases such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere. The main question is how can we control the current situation and build a better world for future generations. It starts with little steps by every individual. Start using cloth bags made from sustainable materials for all shopping purposes, instead of using high-watt lights use energy-efficient bulbs, switch off the electricity, don’t waste water, abolish deforestation and encourage planting more trees. Shift the use of energy from petroleum or other fossil fuels to wind and solar energy. Instead of throwing out the old clothes donate them to someone so that it is recycled. Donate old books, don’t waste paper.  Above all, spread awareness about global warming. Every little thing a person does towards saving the earth will contribute in big or small amounts. We must learn that 1% effort is better than no effort. Pledge to take care of Mother Nature and speak up about global warming.

Also Read: Types of Water Pollution

Global warming isn’t a prediction, it is happening! A person denying it or unaware of it is in the most simple terms complicit. Do we have another planet to live on? Unfortunately, we have been bestowed with this one planet only that can sustain life yet over the years we have turned a blind eye to the plight it is in. Global warming is not an abstract concept but a global phenomenon occurring ever so slowly even at this moment.

Global Warming is a phenomenon that is occurring every minute resulting in a gradual increase in the Earth’s overall climate. Brought about by greenhouse gases that trap the solar radiation in the atmosphere, global warming can change the entire map of the earth, displacing areas, flooding many countries, and destroying multiple lifeforms. Extreme weather is a direct consequence of global warming but it is not an exhaustive consequence. There are virtually limitless effects of global warming which are all harmful to life on earth.

The sea level is increasing by 0.12 inches per year worldwide. This is happening because of the melting of polar ice caps because of global warming. This has increased the frequency of floods in many lowland areas and has caused damage to coral reefs. The Arctic is one of the worst-hit areas affected by global warming. Air quality has been adversely affected and the acidity of the seawater has also increased causing severe damage to marine life forms. Severe natural disasters are brought about by global warming which has had dire effects on life and property.

As long as mankind produces greenhouse gases, global warming will continue to accelerate. The consequences are felt at a much smaller scale which will increase to become drastic shortly. The power to save the day lies in the hands of humans, the need is to seize the day. Energy consumption should be reduced on an individual basis. Fuel-efficient cars and other electronics should be encouraged to reduce the wastage of energy sources. This will also improve air quality and reduce the concentration of greenhouse gases in the atmosphere. Global warming is an evil that can only be defeated when fought together.

It is better late than never. If we all take steps today, we will have a much brighter future tomorrow. Global warming is the bane of our existence and various policies have come up worldwide to fight it but that is not enough. The actual difference is made when we work at an individual level to fight it. Understanding its import now is crucial before it becomes an irrevocable mistake. Exterminating global warming is of utmost importance and each one of us is as responsible for it as the next.  

Always hear about global warming everywhere, but do we know what it is? The evil of the worst form, global warming is a phenomenon that can affect life more fatally. Global warming refers to the increase in the earth’s temperature as a result of various human activities. The planet is gradually getting hotter and threatening the existence of lifeforms on it. Despite being relentlessly studied and researched, global warming for the majority of the population remains an abstract concept of science. It is this concept that over the years has culminated in making global warming a stark reality and not a concept covered in books.

Global warming is not caused by one sole reason that can be curbed. There are multifarious factors that cause global warming most of which are a part of an individual’s daily existence. Burning of fuels for cooking, in vehicles, and for other conventional uses, a large amount of greenhouse gases like carbon dioxide, and methane amongst many others is produced which accelerates global warming. Rampant deforestation also results in global warming as lesser green cover results in an increased presence of carbon dioxide in the atmosphere which is a greenhouse gas. 

Finding a solution to global warming is of immediate importance. Global warming is a phenomenon that has to be fought unitedly. Planting more trees can be the first step that can be taken toward warding off the severe consequences of global warming. Increasing the green cover will result in regulating the carbon cycle. There should be a shift from using nonrenewable energy to renewable energy such as wind or solar energy which causes less pollution and thereby hinder the acceleration of global warming. Reducing energy needs at an individual level and not wasting energy in any form is the most important step to be taken against global warming.

The warning bells are tolling to awaken us from the deep slumber of complacency we have slipped into. Humans can fight against nature and it is high time we acknowledged that. With all our scientific progress and technological inventions, fighting off the negative effects of global warming is implausible. We have to remember that we do not inherit the earth from our ancestors but borrow it from our future generations and the responsibility lies on our shoulders to bequeath them a healthy planet for life to exist. 

Also Read: Essay on Disaster Management

One good action in a day to combat the heat.

Global Warming and Climate Change are two sides of the same coin. Both are interrelated with each other and are two issues of major concern worldwide. Greenhouse gases released such as carbon dioxide, CFCs, and other pollutants in the earth’s atmosphere cause Global Warming which leads to climate change. Black holes have started to form in the ozone layer that protects the earth from harmful ultraviolet rays. Human activities have created climate change and global warming. Industrial waste and fumes are the major contributors to global warming. Another factor affecting is the burning of fossil fuels, deforestation and also one of the reasons for climate change.  Global warming has resulted in shrinking mountain glaciers in Antarctica, Greenland, and the Arctic and causing climate change. Switching from the use of fossil fuels to energy sources like wind and solar. When buying any electronic appliance buy the best quality with energy savings stars. Don’t waste water and encourage rainwater harvesting in your community. 

Also Read: Essay on Air Pollution

Writing an effective essay needs skills that few people possess and even fewer know how to implement. While writing an essay can be an assiduous task that can be unnerving at times, some key pointers can be inculcated to draft a successful essay. These involve focusing on the structure of the essay, planning it out well, and emphasizing crucial details. Mentioned below are some pointers that can help you write better structure and more thoughtful essays that will get across to your readers:

  • Prepare an outline for the essay to ensure continuity and relevance and no break in the structure of the essay
  • Decide on a thesis statement that will form the basis of your essay. It will be the point of your essay and help readers understand your contention
  • Follow the structure of an introduction, a detailed body followed by a conclusion so that the readers can comprehend the essay in a particular manner without any dissonance.
  • Make your beginning catchy and include solutions in your conclusion to make the essay insightful and lucrative to read
  • Reread before putting it out and add your flair to the essay to make it more personal and thereby unique and intriguing for readers  

Relevant Blogs

Ans. Both natural and man-made factors contribute to global warming. The natural one also contains methane gas, volcanic eruptions, and greenhouse gases. Deforestation , mining , livestock raising, burning fossil fuels, and other man-made causes are next.

Ans. The government and the general public can work together to stop global warming. Trees must be planted more often, and deforestation must be prohibited. Auto usage needs to be curbed, and recycling needs to be promoted.

Ans. Switching to renewable energy sources , adopting sustainable farming, transportation, and energy methods, and conserving water and other natural resources.

We hope this blog gave you an idea about how to write and present an essay on global warming that puts forth your opinions. The skill of writing an essay comes in handy when appearing for standardized language tests . Thinking of taking one soon? Leverage Edu provides the best online test prep for the same via Leverage Live . Register today to know more!

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This was really a good essay on global warming… There has been used many unic words..and I really liked it!!!Seriously I had been looking for a essay about Global warming just like this…

Thank you for the comment!

I want to learn how to write essay writing so I joined this page.This page is very useful for everyone.

Hi, we are glad that we could help you to write essays. We have a beginner’s guide to write essays ( https://leverageedu.com/blog/essay-writing/ ) and we think this might help you.

It is not good , to have global warming in our earth .So we all have to afforestation program on all the world.

thank you so much

Very educative , helpful and it is really going to strength my English knowledge to structure my essay in future

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Global warming is the increase in 𝓽𝓱𝓮 ᴀᴠᴇʀᴀɢᴇ ᴛᴇᴍᴘᴇʀᴀᴛᴜʀᴇs ᴏғ ᴇᴀʀᴛʜ🌎 ᴀᴛᴍᴏsᴘʜᴇʀᴇ

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Climate Change Essay

500+ words essay on climate change.

Climate change is a major global challenge today, and the world is becoming more vulnerable to this change. Climate change refers to the changes in Earth’s climate condition. It describes the changes in the atmosphere which have taken place over a period ranging from decades to millions of years. A recent report from the United Nations predicted that the average global temperature could increase by 6˚ Celsius at the end of the century. Climate change has an adverse effect on the environment and ecosystem. With the help of this essay, students will get to know the causes and effects of climate change and possible solutions. Also, they will be able to write essays on similar topics and can boost their writing skills.

What Causes Climate Change?

The Earth’s climate has always changed and evolved. Some of these changes have been due to natural causes such as volcanic eruptions, floods, forest fires etc., but quite a few of them are due to human activities. Human activities such as deforestation, burning fossil fuels, farming livestock etc., generate an enormous amount of greenhouse gases. This results in the greenhouse effect and global warming which are the major causes of climate change.

Effects of Climate Change

If the current situation of climate change continues in a similar manner, then it will impact all forms of life on the earth. The earth’s temperature will rise, the monsoon patterns will change, sea levels will rise, and storms, volcanic eruptions and natural disasters will occur frequently. The biological and ecological balance of the earth will get disturbed. The environment will get polluted and humans will not be able to get fresh air to breathe and fresh water to drink. Life on earth will come to an end.

Steps to be Taken to Reduce Climate Change

The Government of India has taken many measures to improve the dire situation of Climate Change. The Ministry of Environment and Forests is the nodal agency for climate change issues in India. It has initiated several climate-friendly measures, particularly in the area of renewable energy. India took several steps and policy initiatives to create awareness about climate change and help capacity building for adaptation measures. It has initiated a “Green India” programme under which various trees are planted to make the forest land more green and fertile.

We need to follow the path of sustainable development to effectively address the concerns of climate change. We need to minimise the use of fossil fuels, which is the major cause of global warming. We must adopt alternative sources of energy, such as hydropower, solar and wind energy to make a progressive transition to clean energy. Mahatma Gandhi said that “Earth provides enough to satisfy every man’s need, but not any man’s greed”. With this view, we must remodel our outlook and achieve the goal of sustainable development. By adopting clean technologies, equitable distribution of resources and addressing the issues of equity and justice, we can make our developmental process more harmonious with nature.

We hope students liked this essay on Climate Change and gathered useful information on this topic so that they can write essays in their own words. To get more study material related to the CBSE, ICSE, State Board and Competitive exams, keep visiting the BYJU’S website.

Frequently Asked Questions on climate change Essay

What are the reasons for climate change.

1. Deforestation 2. Excessive usage of fossil fuels 3. Water, Soil pollution 4. Plastic and other non-biodegradable waste 5. Wildlife and nature extinction

How can we save this climate change situation?

1. Avoid over usage of natural resources 2. Do not use or buy items made from animals 3. Avoid plastic usage and pollution

Are there any natural causes for climate change?

Yes, some of the natural causes for climate change are: 1. Solar variations 2. Volcanic eruption and tsunamis 3. Earth’s orbital changes

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Essay on Climate Change

Climate Change Essay - The globe is growing increasingly sensitive to climate change. It is currently a serious worldwide concern. The term "Climate Change" describes changes to the earth's climate. It explains the atmospheric changes that have occurred across time, spanning from decades to millions of years. Here are some sample essays on climate change.

100 Words Essay on Climate Change

200 words essay on climate change, 500 words essay on climate change.

Essay on Climate Change

The climatic conditions on Earth are changing due to climate change. Several internal and external variables, such as solar radiation, variations in the Earth's orbit, volcanic eruptions, plate tectonics, etc., are to blame for this.

There are strategies for climate change reduction. If not implemented, the weather might get worse, there might be water scarcity, there could be lower agricultural output, and it might affect people's ability to make a living. In order to breathe clean air and drink pure water, you must concentrate on limiting human activity. These are the simple measures that may be taken to safeguard the environment and its resources.

The climate of the Earth has changed significantly over time. While some of these changes were brought on by natural events like volcanic eruptions, floods, forest fires, etc., many of the changes were brought on by human activity. The burning of fossil fuels, domesticating livestock, and other human activities produce a significant quantity of greenhouse gases. This results in an increase of greenhouse effect and global warming which are the major causes for climate change.

Reasons of Climate Change

Some of the reasons of climate change are:


Excessive use of fossil fuels

Water and soil pollution

Plastic and other non biodegradable waste

Wildlife and nature extinction

Consequences of Climate Change

All kinds of life on earth will be affected by climate change if it continues to change at the same pace. The earth's temperature will increase, the monsoon patterns will shift, the sea level will rise, and there will be more frequent storms, volcano eruptions, and other natural calamities. The earth's biological and ecological equilibrium will be disturbed. Humans won't be able to access clean water or air to breathe when the environment becomes contaminated. The end of life on this earth is imminent. To reduce the issue of climate change, we need to bring social awareness along with strict measures to protect and preserve the natural environment.

A shift in the world's climatic pattern is referred to as climate change. Over the centuries, the climate pattern of our planet has undergone modifications. The amount of carbon dioxide in the atmosphere has significantly grown.

When Did Climate Change Begin

It is possible to see signs of climate change as early as the beginning of the industrial revolution. The pace at which the manufacturers produced things on a large scale required a significant amount of raw materials. Since the raw materials being transformed into finished products now have such huge potential for profit, these business models have spread quickly over the world. Hazardous substances and chemicals build up in the environment as a result of company emissions and waste disposal.

Although climate change is a natural occurrence, it is evident that human activity is turning into the primary cause of the current climate change situation. The major cause is the growing population. Natural resources are utilised more and more as a result of the population's fast growth placing a heavy burden on the available resources. Over time, as more and more products and services are created, pollution will eventually increase.

Causes of Climate Change

There are a number of factors that have contributed towards weather change in the past and continue to do so. Let us look at a few:

Solar Radiation |The climate of earth is determined by how quickly the sun's energy is absorbed and distributed throughout space. This energy is transmitted throughout the world by the winds, ocean currents etc which affects the climatic conditions of the world. Changes in solar intensity have an effect on the world's climate.

Deforestation | The atmosphere's carbon dioxide is stored by trees. As a result of their destruction, carbon dioxide builds up more quickly since there are no trees to absorb it. Additionally, trees release the carbon they stored when we burn them.

Agriculture | Many kinds of greenhouse gases are released into the atmosphere by growing crops and raising livestock. Animals, for instance, create methane, a greenhouse gas that is 30 times more potent than carbon dioxide. The nitrous oxide used in fertilisers is roughly 300 times more strong than carbon dioxide.

How to Prevent Climate Change

We need to look out for drastic steps to stop climate change since it is affecting the resources and life on our planet. We can stop climate change if the right solutions are put in place. Here are some strategies for reducing climate change:

Raising public awareness of climate change

Prohibiting tree-cutting and deforestation.

Ensure the surroundings are clean.

Refrain from using chemical fertilisers.

Water and other natural resource waste should be reduced.

Protect the animals and plants.

Purchase energy-efficient goods and equipment.

Increase the number of trees in the neighbourhood and its surroundings.

Follow the law and safeguard the environment's resources.

Reduce the amount of energy you use.

During the last few decades especially, climate change has grown to be of concern. Global concern has been raised over changes in the Earth's climatic pattern. The causes of climate change are numerous, as well as the effects of it and it is our responsibility as inhabitants of this planet to look after its well being and leave it in a better condition for future generations.

Explore Career Options (By Industry)

  • Construction
  • Entertainment
  • Manufacturing
  • Information Technology

Bio Medical Engineer

The field of biomedical engineering opens up a universe of expert chances. An Individual in the biomedical engineering career path work in the field of engineering as well as medicine, in order to find out solutions to common problems of the two fields. The biomedical engineering job opportunities are to collaborate with doctors and researchers to develop medical systems, equipment, or devices that can solve clinical problems. Here we will be discussing jobs after biomedical engineering, how to get a job in biomedical engineering, biomedical engineering scope, and salary. 

Data Administrator

Database professionals use software to store and organise data such as financial information, and customer shipping records. Individuals who opt for a career as data administrators ensure that data is available for users and secured from unauthorised sales. DB administrators may work in various types of industries. It may involve computer systems design, service firms, insurance companies, banks and hospitals.

GIS officer work on various GIS software to conduct a study and gather spatial and non-spatial information. GIS experts update the GIS data and maintain it. The databases include aerial or satellite imagery, latitudinal and longitudinal coordinates, and manually digitized images of maps. In a career as GIS expert, one is responsible for creating online and mobile maps.

Ethical Hacker

A career as ethical hacker involves various challenges and provides lucrative opportunities in the digital era where every giant business and startup owns its cyberspace on the world wide web. Individuals in the ethical hacker career path try to find the vulnerabilities in the cyber system to get its authority. If he or she succeeds in it then he or she gets its illegal authority. Individuals in the ethical hacker career path then steal information or delete the file that could affect the business, functioning, or services of the organization.

Data Analyst

The invention of the database has given fresh breath to the people involved in the data analytics career path. Analysis refers to splitting up a whole into its individual components for individual analysis. Data analysis is a method through which raw data are processed and transformed into information that would be beneficial for user strategic thinking.

Data are collected and examined to respond to questions, evaluate hypotheses or contradict theories. It is a tool for analyzing, transforming, modeling, and arranging data with useful knowledge, to assist in decision-making and methods, encompassing various strategies, and is used in different fields of business, research, and social science.

Database Architect

If you are intrigued by the programming world and are interested in developing communications networks then a career as database architect may be a good option for you. Data architect roles and responsibilities include building design models for data communication networks. Wide Area Networks (WANs), local area networks (LANs), and intranets are included in the database networks. It is expected that database architects will have in-depth knowledge of a company's business to develop a network to fulfil the requirements of the organisation. Stay tuned as we look at the larger picture and give you more information on what is db architecture, why you should pursue database architecture, what to expect from such a degree and what your job opportunities will be after graduation. Here, we will be discussing how to become a data architect. Students can visit NIT Trichy , IIT Kharagpur , JMI New Delhi . 

Geothermal Engineer

Individuals who opt for a career as geothermal engineers are the professionals involved in the processing of geothermal energy. The responsibilities of geothermal engineers may vary depending on the workplace location. Those who work in fields design facilities to process and distribute geothermal energy. They oversee the functioning of machinery used in the field.

Geotechnical engineer

The role of geotechnical engineer starts with reviewing the projects needed to define the required material properties. The work responsibilities are followed by a site investigation of rock, soil, fault distribution and bedrock properties on and below an area of interest. The investigation is aimed to improve the ground engineering design and determine their engineering properties that include how they will interact with, on or in a proposed construction. 

The role of geotechnical engineer in mining includes designing and determining the type of foundations, earthworks, and or pavement subgrades required for the intended man-made structures to be made. Geotechnical engineering jobs are involved in earthen and concrete dam construction projects, working under a range of normal and extreme loading conditions. 

Bank Probationary Officer (PO)

A career as Bank Probationary Officer (PO) is seen as a promising career opportunity and a white-collar career. Each year aspirants take the Bank PO exam . This career provides plenty of career development and opportunities for a successful banking future. If you have more questions about a career as  Bank Probationary Officer (PO),  what is probationary officer  or how to become a Bank Probationary Officer (PO) then you can read the article and clear all your doubts. 

Finance Executive

A career as a Finance Executive requires one to be responsible for monitoring an organisation's income, investments and expenses to create and evaluate financial reports. His or her role involves performing audits, invoices, and budget preparations. He or she manages accounting activities, bank reconciliations, and payable and receivable accounts.  

Investment Banker

An Investment Banking career involves the invention and generation of capital for other organizations, governments, and other entities. Individuals who opt for a career as Investment Bankers are the head of a team dedicated to raising capital by issuing bonds. Investment bankers are termed as the experts who have their fingers on the pulse of the current financial and investing climate. Students can pursue various Investment Banker courses, such as Banking and Insurance , and  Economics to opt for an Investment Banking career path.

Bank Branch Manager

Bank Branch Managers work in a specific section of banking related to the invention and generation of capital for other organisations, governments, and other entities. Bank Branch Managers work for the organisations and underwrite new debts and equity securities for all type of companies, aid in the sale of securities, as well as help to facilitate mergers and acquisitions, reorganisations, and broker trades for both institutions and private investors.

Treasury analyst career path is often regarded as certified treasury specialist in some business situations, is a finance expert who specifically manages a company or organisation's long-term and short-term financial targets. Treasurer synonym could be a financial officer, which is one of the reputed positions in the corporate world. In a large company, the corporate treasury jobs hold power over the financial decision-making of the total investment and development strategy of the organisation.


An underwriter is a person who assesses and evaluates the risk of insurance in his or her field like mortgage, loan, health policy, investment, and so on and so forth. The underwriter career path does involve risks as analysing the risks means finding out if there is a way for the insurance underwriter jobs to recover the money from its clients. If the risk turns out to be too much for the company then in the future it is an underwriter who will be held accountable for it. Therefore, one must carry out his or her job with a lot of attention and diligence.

Product Manager

A Product Manager is a professional responsible for product planning and marketing. He or she manages the product throughout the Product Life Cycle, gathering and prioritising the product. A product manager job description includes defining the product vision and working closely with team members of other departments to deliver winning products.  

Transportation Planner

A career as Transportation Planner requires technical application of science and technology in engineering, particularly the concepts, equipment and technologies involved in the production of products and services. In fields like land use, infrastructure review, ecological standards and street design, he or she considers issues of health, environment and performance. A Transportation Planner assigns resources for implementing and designing programmes. He or she is responsible for assessing needs, preparing plans and forecasts and compliance with regulations.

Conservation Architect

A Conservation Architect is a professional responsible for conserving and restoring buildings or monuments having a historic value. He or she applies techniques to document and stabilise the object’s state without any further damage. A Conservation Architect restores the monuments and heritage buildings to bring them back to their original state.

Safety Manager

A Safety Manager is a professional responsible for employee’s safety at work. He or she plans, implements and oversees the company’s employee safety. A Safety Manager ensures compliance and adherence to Occupational Health and Safety (OHS) guidelines.

A Team Leader is a professional responsible for guiding, monitoring and leading the entire group. He or she is responsible for motivating team members by providing a pleasant work environment to them and inspiring positive communication. A Team Leader contributes to the achievement of the organisation’s goals. He or she improves the confidence, product knowledge and communication skills of the team members and empowers them.

Structural Engineer

A Structural Engineer designs buildings, bridges, and other related structures. He or she analyzes the structures and makes sure the structures are strong enough to be used by the people. A career as a Structural Engineer requires working in the construction process. It comes under the civil engineering discipline. A Structure Engineer creates structural models with the help of computer-aided design software. 

Individuals in the architecture career are the building designers who plan the whole construction keeping the safety and requirements of the people. Individuals in architect career in India provides professional services for new constructions, alterations, renovations and several other activities. Individuals in architectural careers in India visit site locations to visualize their projects and prepare scaled drawings to submit to a client or employer as a design. Individuals in architecture careers also estimate build costs, materials needed, and the projected time frame to complete a build.

Landscape Architect

Having a landscape architecture career, you are involved in site analysis, site inventory, land planning, planting design, grading, stormwater management, suitable design, and construction specification. Frederick Law Olmsted, the designer of Central Park in New York introduced the title “landscape architect”. The Australian Institute of Landscape Architects (AILA) proclaims that "Landscape Architects research, plan, design and advise on the stewardship, conservation and sustainability of development of the environment and spaces, both within and beyond the built environment". Therefore, individuals who opt for a career as a landscape architect are those who are educated and experienced in landscape architecture. Students need to pursue various landscape architecture degrees, such as  M.Des , M.Plan to become landscape architects. If you have more questions regarding a career as a landscape architect or how to become a landscape architect then you can read the article to get your doubts cleared. 

An expert in plumbing is aware of building regulations and safety standards and works to make sure these standards are upheld. Testing pipes for leakage using air pressure and other gauges, and also the ability to construct new pipe systems by cutting, fitting, measuring and threading pipes are some of the other more involved aspects of plumbing. Individuals in the plumber career path are self-employed or work for a small business employing less than ten people, though some might find working for larger entities or the government more desirable.

Orthotist and Prosthetist

Orthotists and Prosthetists are professionals who provide aid to patients with disabilities. They fix them to artificial limbs (prosthetics) and help them to regain stability. There are times when people lose their limbs in an accident. In some other occasions, they are born without a limb or orthopaedic impairment. Orthotists and prosthetists play a crucial role in their lives with fixing them to assistive devices and provide mobility.

Veterinary Doctor

A veterinary doctor is a medical professional with a degree in veterinary science. The veterinary science qualification is the minimum requirement to become a veterinary doctor. There are numerous veterinary science courses offered by various institutes. He or she is employed at zoos to ensure they are provided with good health facilities and medical care to improve their life expectancy.


A career in pathology in India is filled with several responsibilities as it is a medical branch and affects human lives. The demand for pathologists has been increasing over the past few years as people are getting more aware of different diseases. Not only that, but an increase in population and lifestyle changes have also contributed to the increase in a pathologist’s demand. The pathology careers provide an extremely huge number of opportunities and if you want to be a part of the medical field you can consider being a pathologist. If you want to know more about a career in pathology in India then continue reading this article.


Gynaecology can be defined as the study of the female body. The job outlook for gynaecology is excellent since there is evergreen demand for one because of their responsibility of dealing with not only women’s health but also fertility and pregnancy issues. Although most women prefer to have a women obstetrician gynaecologist as their doctor, men also explore a career as a gynaecologist and there are ample amounts of male doctors in the field who are gynaecologists and aid women during delivery and childbirth. 

Ophthalmic Medical Technician

Ophthalmic technician careers are one of the booming careers option available in the field of healthcare. Being a part of this field as an ophthalmic medical technician can provide several career opportunities for an individual. With advancing technology the job of individuals who opt for a career as ophthalmic medical technicians have become of even more importance as he or she is required to assist the ophthalmologist in using different types of machinery. If you want to know more about the field and what are the several job opportunities, work environment, just about anything continues reading the article and all your questions shall be answered.

Radiation Therapist

People might think that a radiation therapist only spends most of his/her time in a radiation operation unit but that’s not the case. In reality, a radiation therapist’s job is not as easy as it seems. The job of radiation therapist requires him/her to be attentive, hardworking, and dedicated to his/her work hours. A radiation therapist is on his/her feet for a long duration and might be required to lift or turn disabled patients. Because a career as a radiation therapist involves working with radiation and radioactive material, a radiation therapist is required to follow the safety procedures in order to make sure that he/she is not exposed to a potentially harmful amount of radiation.

Recreational Worker

A recreational worker is a professional who designs and leads activities to provide assistance to people to adopt a healthy lifestyle. He or she instructs physical exercises and games to have fun and improve fitness. A recreational worker may work in summer camps, fitness and recreational sports centres, nature parks, nursing care facilities, and other settings. He or she may lead crafts, sports, music, games, drama and other activities.


A career as paediatrician has emerged as one of India's most popular career choices. By choosing a career as paediatrician, not only in India but also overseas, one can find lucrative work profiles as demand for talented and professional paediatricians is increasing day by day. If you are passionate about children and have the patience to evaluate and diagnose their issues, you may have a good career as paediatricians. Paediatricians take care of children's physical, mental and emotional health from infancy to adolescence.

For an individual who opts for a career as an actor, the primary responsibility is to completely speak to the character he or she is playing and to persuade the crowd that the character is genuine by connecting with them and bringing them into the story. This applies to significant roles and littler parts, as all roles join to make an effective creation. Here in this article, we will discuss how to become an actor in India, actor exams, actor salary in India, and actor jobs. 

Individuals who opt for a career as acrobats create and direct original routines for themselves, in addition to developing interpretations of existing routines. The work of circus acrobats can be seen in a variety of performance settings, including circus, reality shows, sports events like the Olympics, movies and commercials. Individuals who opt for a career as acrobats must be prepared to face rejections and intermittent periods of work. The creativity of acrobats may extend to other aspects of the performance. For example, acrobats in the circus may work with gym trainers, celebrities or collaborate with other professionals to enhance such performance elements as costume and or maybe at the teaching end of the career.

Video Game Designer

Career as a video game designer is filled with excitement as well as responsibilities. A video game designer is someone who is involved in the process of creating a game from day one. He or she is responsible for fulfilling duties like designing the character of the game, the several levels involved, plot, art and similar other elements. Individuals who opt for a career as a video game designer may also write the codes for the game using different programming languages. Depending on the video game designer job description and experience they may also have to lead a team and do the early testing of the game in order to suggest changes and find loopholes.

Talent Agent

The career as a Talent Agent is filled with responsibilities. A Talent Agent is someone who is involved in the pre-production process of the film. It is a very busy job for a Talent Agent but as and when an individual gains experience and progresses in the career he or she can have people assisting him or her in work. Depending on one’s responsibilities, number of clients and experience he or she may also have to lead a team and work with juniors under him or her in a talent agency. In order to know more about the job of a talent agent continue reading the article.

If you want to know more about talent agent meaning, how to become a Talent Agent, or Talent Agent job description then continue reading this article.

Radio Jockey

Radio Jockey is an exciting, promising career and a great challenge for music lovers. If you are really interested in a career as radio jockey, then it is very important for an RJ to have an automatic, fun, and friendly personality. If you want to get a job done in this field, a strong command of the language and a good voice are always good things. Apart from this, in order to be a good radio jockey, you will also listen to good radio jockeys so that you can understand their style and later make your own by practicing.

A career as radio jockey has a lot to offer to deserving candidates. If you want to know more about a career as radio jockey, and how to become a radio jockey then continue reading the article.

Fashion Blogger

Fashion bloggers use multiple social media platforms to recommend or share ideas related to fashion. A fashion blogger is a person who writes about fashion, publishes pictures of outfits, jewellery, accessories. Fashion blogger works as a model, journalist, and a stylist in the fashion industry. In current fashion times, these bloggers have crossed into becoming a star in fashion magazines, commercials, or campaigns. 


The word “choreography" actually comes from Greek words that mean “dance writing." Individuals who opt for a career as a choreographer create and direct original dances, in addition to developing interpretations of existing dances. A Choreographer dances and utilises his or her creativity in other aspects of dance performance. For example, he or she may work with the music director to select music or collaborate with other famous choreographers to enhance such performance elements as lighting, costume and set design.

Social Media Manager

A career as social media manager involves implementing the company’s or brand’s marketing plan across all social media channels. Social media managers help in building or improving a brand’s or a company’s website traffic, build brand awareness, create and implement marketing and brand strategy. Social media managers are key to important social communication as well.

Copy Writer

In a career as a copywriter, one has to consult with the client and understand the brief well. A career as a copywriter has a lot to offer to deserving candidates. Several new mediums of advertising are opening therefore making it a lucrative career choice. Students can pursue various copywriter courses such as Journalism , Advertising , Marketing Management . Here, we have discussed how to become a freelance copywriter, copywriter career path, how to become a copywriter in India, and copywriting career outlook. 

Careers in journalism are filled with excitement as well as responsibilities. One cannot afford to miss out on the details. As it is the small details that provide insights into a story. Depending on those insights a journalist goes about writing a news article. A journalism career can be stressful at times but if you are someone who is passionate about it then it is the right choice for you. If you want to know more about the media field and journalist career then continue reading this article.

For publishing books, newspapers, magazines and digital material, editorial and commercial strategies are set by publishers. Individuals in publishing career paths make choices about the markets their businesses will reach and the type of content that their audience will be served. Individuals in book publisher careers collaborate with editorial staff, designers, authors, and freelance contributors who develop and manage the creation of content.

In a career as a vlogger, one generally works for himself or herself. However, once an individual has gained viewership there are several brands and companies that approach them for paid collaboration. It is one of those fields where an individual can earn well while following his or her passion. Ever since internet cost got reduced the viewership for these types of content has increased on a large scale. Therefore, the career as vlogger has a lot to offer. If you want to know more about the career as vlogger, how to become a vlogger, so on and so forth then continue reading the article. Students can visit Jamia Millia Islamia , Asian College of Journalism , Indian Institute of Mass Communication to pursue journalism degrees.

Individuals in the editor career path is an unsung hero of the news industry who polishes the language of the news stories provided by stringers, reporters, copywriters and content writers and also news agencies. Individuals who opt for a career as an editor make it more persuasive, concise and clear for readers. In this article, we will discuss the details of the editor's career path such as how to become an editor in India, editor salary in India and editor skills and qualities.

Multimedia Specialist

A multimedia specialist is a media professional who creates, audio, videos, graphic image files, computer animations for multimedia applications. He or she is responsible for planning, producing, and maintaining websites and applications. 

Corporate Executive

Are you searching for a Corporate Executive job description? A Corporate Executive role comes with administrative duties. He or she provides support to the leadership of the organisation. A Corporate Executive fulfils the business purpose and ensures its financial stability. In this article, we are going to discuss how to become corporate executive.

Linguistic meaning is related to language or Linguistics which is the study of languages. A career as a linguistic meaning, a profession that is based on the scientific study of language, and it's a very broad field with many specialities. Famous linguists work in academia, researching and teaching different areas of language, such as phonetics (sounds), syntax (word order) and semantics (meaning). 

Other researchers focus on specialities like computational linguistics, which seeks to better match human and computer language capacities, or applied linguistics, which is concerned with improving language education. Still, others work as language experts for the government, advertising companies, dictionary publishers and various other private enterprises. Some might work from home as freelance linguists. Philologist, phonologist, and dialectician are some of Linguist synonym. Linguists can study French , German , Italian . 

Production Manager

Production Manager Job Description: A Production Manager is responsible for ensuring smooth running of manufacturing processes in an efficient manner. He or she plans and organises production schedules. The role of Production Manager involves estimation, negotiation on budget and timescales with the clients and managers. 

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Production Engineer

A career as Production Engineer is crucial in the manufacturing industry. He or she ensures the functionality of production equipment and machinery to improve productivity and minimize production costs in order to drive revenues and increase profitability. 

Textile Engineer

An individual in textile engineering jobs is creative and innovative that involves the application of scientific laws and principles in everyday work responsibilities. Textile engineering jobs include designing fiber processing systems and related machinery involved in the manufacturing of fiber, cloth, apparel and other related products.

Automation Test Engineer

An Automation Test Engineer job involves executing automated test scripts. He or she identifies the project’s problems and troubleshoots them. The role involves documenting the defect using management tools. He or she works with the application team in order to resolve any issues arising during the testing process. 

R&D Personnel

A career as R&D Personnel requires researching, planning, and implementing new programs and protocols into their organization and overseeing new products’ development. He or she uses his or her creative abilities to improve the existing products as per the requirements of the target market.

Product Designer

Individuals who opt for a career as product designers are responsible for designing the components and overall product concerning its shape, size, and material used in manufacturing. They are responsible for the aesthetic appearance of the product. A product designer uses his or her creative skills to give a product its final outlook and ensures the functionality of the design. 

Students can opt for various product design degrees such as B.Des and M.Des to become product designers. Industrial product designer prepares 3D models of designs for approval and discusses them with clients and other colleagues. Individuals who opt for a career as a product designer estimate the total cost involved in designing.

Welding Engineer

Welding Engineer Job Description: A Welding Engineer work involves managing welding projects and supervising welding teams. He or she is responsible for reviewing welding procedures, processes and documentation. A career as Welding Engineer involves conducting failure analyses and causes on welding issues. 

Information Security Manager

Individuals in the information security manager career path involves in overseeing and controlling all aspects of computer security. The IT security manager job description includes planning and carrying out security measures to protect the business data and information from corruption, theft, unauthorised access, and deliberate attack 

Computer Programmer

Careers in computer programming primarily refer to the systematic act of writing code and moreover include wider computer science areas. The word 'programmer' or 'coder' has entered into practice with the growing number of newly self-taught tech enthusiasts. Computer programming careers involve the use of designs created by software developers and engineers and transforming them into commands that can be implemented by computers. These commands result in regular usage of social media sites, word-processing applications and browsers.

ITSM Manager

ITSM Manager is a professional responsible for heading the ITSM (Information Technology Service Management) or (Information Technology Infrastructure Library) processes. He or she ensures that operation management provides appropriate resource levels for problem resolutions. The ITSM Manager oversees the level of prioritisation for the problems, critical incidents, planned as well as proactive tasks. 

Big Data Analytics Engineer

Big Data Analytics Engineer Job Description: A Big Data Analytics Engineer is responsible for collecting data from various sources. He or she has to sort the organised and chaotic data to find out patterns. The role of Big Data Engineer involves converting messy information into useful data that is clean, accurate and actionable. 

Integration Architect

Career  as  Integration Architect is responsible for integrating various systems and technologies into the whole. He or she creates technical designs for complex systems as well as plans for security, scalability and back up procedures. Integration Architect oversees all stages of the software development process concerning from planning to deployment. 

Information Architect

An Information Architect Is a professional who helps organizations collect, manage, and convert their data into usable information. He/she also provides this information to business analysts and data scientists for future predictions. The main objective of this role is to make data accessible to improve the performance of an organization.

Test Analyst

Test Analyst Job Description: A Test Analyst is responsible for ensuring functionality of computer software and hardware equipment, or other products depending on the industry before setting them into the market. His or her role involves designing, developing and administering a series of tests and evaluating them. The role demands to identify potential issues with the product. 

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academic essay on climate change

Climate Change Essay

500+ words essay on climate change.

Climate change is the shift of weather patterns and conditions. We are experiencing rapid change in the climate due to various factors. Needless to say, our earth is experiencing rising global temperatures. Do you think it is a matter of concern? Well yes, you might have heard about the melting glaciers which is resulting in rising sea levels. There has been a drastic change in the climate due to hazardous factors such as pollution, burning coals, industrial waste disposal in the air, etc. All this will result in affecting the environment and its resources. To overcome the issue of climate change, you need to bring social awareness along with stringent measures to protect and preserve the environment. In this climate change essay, we are going to discuss the factors and how to prevent climate change. 

What is Climate Change? 

Climate change is the change in the average weather conditions. We can say that climate change is responsible for change in the normal climatic conditions. These changes result in heavy storms, heat waves, floods, melting glaciers, etc. Our earth is going through a lot of changes with respect to climate, which is impacting the livelihood of people and other living things. Global warming is one aspect of climate change. Due to these factors, carbon dioxide and greenhouse gases are released in the atmosphere. Check out the following causes of climate change given below. 

Climate Change Factors Essay 

Nowadays, we experience extreme weather conditions whether it is cold, heat or rain. Some of the forces or factors that contribute to climate change are greenhouse gas emission, burning of coal, deforestation, air pollution, industrial gas, etc. These factors lead to major climatic change in the earth. Did you know that climate change leads to disastrous events? Yes, it affects the livelihood, health and the resources. It also impacts the water, air and the land we live in. It leads to extreme weather conditions such as droughts, heavy rain, floods, storms, heat waves, forest fires, etc. Moreover, it reduces the quality of drinking water, damages property, pollutes the air and also leads to loss of life. Additionally, it is impacting the life of flora and fauna around us. We need to take extreme measures to prevent climate change. 

Also explore: Learn more about the environment and climate change with Environment essay and Global warming Essay .

How To Prevent Climate Change Essay 

As climate change is hampering the lives and resources of our earth, we need to look out for extreme measures to prevent climate change. Now, what can we do to prevent this? Is it possible for all of us to join and preserve nature? Yes, we can if appropriate strategies are implemented to combat climate change. The different ways to reduce climate change are mentioned below:

  • Make policies and agreements on climate change.
  • Implement projects on clean energy.
  • Create social awareness on climate change. 
  • Prohibit deforestation and cutting down trees.
  • Conduct capacity building programs on climate change. 
  • Keep the surroundings clean. 
  • Avoid use of chemical fertilizers.
  • Reduce wastage of water and other natural resources. 
  • Protect the flora and fauna. 
  • Buy energy efficient products and appliances. 
  • Plant more trees in the neighbourhood and surrounding areas. 
  • Respect the environment and protect its resources. 
  • Reduce the consumption of energy.

These are the ways to reduce climate change. If not implemented, you might see an increase in the weather conditions, shortage of drinking water, agricultural yields, and impact on livelihood. Therefore, you must focus on reducing anthropogenic activities so that you can breathe fresh air and drink clean water. These are the small steps to protect the environment and its resources.

We hope this climate change essay was useful to you. Check Osmo’s essays for kids to explore more essays on a wide variety of topics. 

Frequently Asked Questions On Climate Change Essay

What is a climate change essay.

The climate change essay is information on changing weather conditions and its impact on the environment.

How to start a climate change essay?

You can start a climate change essay with an introduction, factors, and the ways to prevent climate change.

What are the main causes of climate change?

The main causes of climate change are deforestation, burning oils, chemical fertilizers, pollution and release of industrial waste in the air, etc.

To find more information, explore related articles such as technology essay and essay on internet . 


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