The evidence is overwhelming. Different records show that the Earth is warming fast, and that all the heat-trapping emissions we release into the atmosphere from burning fossil fuels is changing our climate.
The time to act is now. But, many powerful industry interests have hindered action and have, largely through surrogates, spread dangerous myths about climate change.
One of the preferred tactics these groups use to sow confusion is to promote studies that either ignore or misrepresent the evidence of thousands of articles published in well-established and well-respected scientific journals, which show that global warming is happening and that it is caused by humans.
No matter how much contrarians try to cloak reality, the evidence is not going away.
Widespread scientific consensus
Scientists worldwide agree that global warming is happening, and that human activity causes it.
The IPCC Fifth Assessment Report (AR5), written by a panel of hundreds of climate experts and scientists from member countries of the World Meteorological Organization the United Nations Environmental Programme, plus a team of external reviewers, states unambiguously:
Human influence on the climate system is clear, and recent anthropogenic emissions of green-house gases are the highest in history. […] Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia.
The scientific consensus is clear. Building on two previousstudies, a landmark 2013 peer-reviewed study evaluated 10,306 scientists to confirm that over 97 percent climate scientists agree, and over 97 percent of scientific articles find that global warming is real and largely caused by humans.
A more recent peer-reviewed paper examined existing studies on consensus in climate research, and concluded that the 97 percent estimate is robust.
This level of consensus is equivalent to the level of agreement among scientists that smoking causes cancer – a statement that very few people, if any, contest today.
The American public also increasingly agrees that global warming is happening. A 2016 poll from Yale found that 70 percent of Americans believe global warming is happening, while record low number of Americans (12 percent) say the opposite.
A Gallup poll from 2017 showed that the number of Americans who worry “a great deal” about global warming has increased from 37 percent in 2016 to 45 percent in 2017. The acceptance of human-caused emissions as the cause of warming is not keeping pace with those that believe it is happening, but it is at 53 percent.
There is no shortage of published research on the consensus of climate scientists and climate science when it comes to human-caused global warming. In addition to the references above, you can read about how the discussion on consensus developed over time in thesestudies.
Many different scientific societies in the United States and numerous national academies of science from around the world have also issued statements that verify the scientific claims about human-caused warming (see below).
Consensus and scientific uncertainty
Climate skeptics and deniers often misrepresent “scientific uncertainty” to undermine climate science findings. Therefore, when it comes to scientific consensus on global warming, it is important to clarify what type of uncertainty exists, and what type does not: there is strong certainty on the types of impacts that global warming is causing (or would be likely to cause under a given scenario for emissions), but less certainty on the exact timing and intensity of these impacts.
For instance, on the issue of sea level rise, we know with certainty that it will happen – it is already happening – and projections under different scenarios give us a range of possible rise. We don’t know an exact value, however, for future sea level rise, because in large part it is dependent on the rate of future emissions, which is unknown.
If emissions continue in a “business as usual” fashion, the sea level rise will be closer to the higher range of projections. But if we significantly reduce emissions, the rise will be closer to the lower levels of projections.
The same is true for how much warming will actually happen, or how much land-based ice and glaciers will melt. All these things are already happening, but future rates are not known because they, too, depend on the rate of future emissions. What scientists can calculate quite confidently is a narrow range of outcomes within a given scenario—meaning the likely highest and lowest values if we continue on a certain path of emissions. This information is critical to making smart collective choices and for planning for the future.
Uncertainties are not a reason to delay action on climate change. Quite the contrary: those uncertainties are really a consequence of our collective choices, and a risk we must prepare for.
You can think about it like car insurance: everyone hopes they won’t be in a car accident but have accident insurance anyway, even though the likelihood is very low.
Climate adaptation and climate risk reduction are “insurance” against the effects of climate change, which in contrast are NOT low-probability events, but highly likely and predicted with high levels of certainty under specific conditions. Being prepared for these scenarios is simply smart planning. Nobody wants to be caught unaware and unprepared.
Many scientific societies and academies have released statements and studies that highlight the overwhelming consensus on climate change science.
American Association for the Advancement of Science: AAAS Reaffirms the Reality of Human-Caused Climate Change
“Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research concludes that the greenhouse gases emitted by human activities are the primary driver. This conclusion is based on multiple independent lines of evidence and the vast body of peer-reviewed science.” (June 2016)
American Chemical Society: Statement on Global Climate Change
“The Earth’s climate is changing in response to increasing concentrations of greenhouse gases (GHGs) and particulate matter in the atmosphere, largely as the result of human activities. … Unmitigated climate change will lead to increases in extreme weather events and will cause significant sea level rise, causing property damage and population displacement. It also will continue to degrade ecosystems and natural resources, affecting food and water availability and human health, further burdening economies and societies. Continued uncontrolled GHG emissions will accelerate and compound the effects and risks of climate change well into the future.” (2016)
American Geophysical Union: Human-induced Climate Change Requires Urgent Action.
"Extensive, independent observations confirm the reality of global warming. These observations show large-scale increases in air and sea temperatures, sea level, and atmospheric water vapor; they document decreases in the extent of mountain glaciers, snow cover, permafrost, and Arctic sea ice. These changes are broadly consistent with long-understood physics and predictions of how the climate system is expected to respond to human-caused increases in greenhouse gases. The changes are inconsistent with explanations of climate change that rely on known natural influences.”(December 2003, revised and reaffirmed December 2007, February 2012, August 2013)
American Meteorological Society:Climate Change: An Information Statement of the American Meteorological Society
"It is clear from extensive scientific evidence that the dominant cause of the rapid change in climate of the past half century is human-induced increases in the amount of atmospheric greenhouse gases, including carbon dioxide (CO2), chlorofluorocarbons, methane, and nitrous oxide.” (August 2012)
American Physical Society: Statement on Earth’s Changing Climate
"While natural sources of climate variability are significant, multiple lines of evidence indicate that human influences have had an increasingly dominant effect on global climate warming observed since the mid-twentieth century. Although the magnitudes of future effects are uncertain, human influences on the climate are growing." (November 2015)
Geological Society of America: Position Statement on Climate Change
"Scientific advances have greatly reduced previous uncertainties about recent global warming. Ground-station measurements have shown a warming trend of ~0.85 °C since 1880, a trend consistent with (1) retreat of northern hemisphere snow and Arctic sea ice; (2) greater heat storage in the ocean; (3) retreat of most mountain glaciers; (4) an ongoing rise in global sea level; and (5) proxy reconstructions of temperature change over past centuries from archives that include ice cores, tree rings, lake sediments, boreholes, cave deposits, and corals." (October 2006; revised April 2010, March 2013, April 2015).
Intergovernmental Panel on Climate Change:Synthesis Report Summary for Policymakers
“Human influence on the climate system is clear, and recent anthropogenic emissions of green-house gases are the highest in history. Recent climate changes have had widespread impacts on human and natural systems. “Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, and sea level has risen.” (2014)
International academies joint statement:Global response to climate change
"Climate change is real. There will always be uncertainty in understanding a system as complex as the world’s climate. However, there is now strong evidence that significant global warming is occurring." (2005, national academies of science of Brazil, China, France, Germany, India, Italy, Japan, Russia, United Kingdom, United States)
U.S. Global Change Research Program: Highlights of the Findings of the U.S. Global Change Research Program Climate Science Special Report
“Based on extensive evidence, … it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence.
“In addition to warming, many other aspects of global climate are changing, primarily in response to human activities. Thousands of studies conducted by researchers around the world have documented changes in surface, atmospheric, and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapor.” (November 2017)
U.S. National Academy of Sciences: Understanding and Responding to Climate Change
"The scientific understanding of climate change is now sufficiently clear to begin taking steps to prepare for climate change and to slow it." (2008)
Image: IPCC AR5
Image: IPCC Assesment Report 5 Cover
Scientific consensus on climate change.
Illustration: John Cook
Yale Program on Climate Communication
Image: David Harp
The 97% consensus on global warming
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What the science says...
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That humans are causing global warming is the position of the Academies of Science from 80 countries plus many scientific organizations that study climate science. More specifically, around 95% of active climate researchers actively publishing climate papers endorse the consensus position.
Consensus on Consensus - Cook et al. (2016)
Authors of seven climate consensus studies — including Naomi Oreskes, Peter Doran, William Anderegg, Bart Verheggen, Ed Maibach, J. Stuart Carlton, and John Cook — co-authored a paper that should settle the expert climate consensus question once and for all. The two key conclusions from the paper are:
1) Depending on exactly how you measure the expert consensus, it’s somewhere between 90% and 100% that agree humans are responsible for climate change, with most of our studies finding 97% consensus among publishing climate scientists.
2) The greater the climate expertise among those surveyed, the higher the consensus on human-caused global warming.
Expert consensus results on the question of human-caused global warming among the previous studies published by the co-authors of Cook et al. (2016). Illustration: John Cook. Available on the SkS Graphics page
Scientific consensus on human-caused global warming as compared to the expertise of the surveyed sample. There’s a strong correlation between consensus and climate science expertise. Illustration: John Cook. Available on the SkS Graphics page
Expert consensus is a powerful thing. People know we don’t have the time or capacity to learn about everything, and so we frequently defer to the conclusions of experts. It’s why we visit doctors when we’re ill. The same is true of climate change: most people defer to the expert consensus of climate scientists. Crucially, as we note in our paper:
Public perception of the scientific consensus has been found to be a gateway belief, affecting other climate beliefs and attitudes including policy support.
That’s why those who oppose taking action to curb climate change have engaged in a misinformation campaign to deny the existence of the expert consensus. They’ve been largely successful, as the public badly underestimate the expert consensus, in what we call the “consensus gap.” Only 16% of Americans realize that the consensus is above 90%.
Lead author John Cook explaining the team’s 2016 consensus paper.
Skeptical Science's 2013 'The Consensus Project'
Scientists need to back up their opinions with research and data that survive the peer-review process. A Skeptical Science peer-reviewed survey of all (over 12,000) peer-reviewed abstracts on the subject 'global climate change' and 'global warming' published between 1991 and 2011 (Cook et al. 2013) found that over 97% of the papers taking a position on the subject agreed with the consensus position that humans are causing global warming. In a second phase of the project, the scientist authors were emailed and rated over 2,000 of their own papers. Once again, over 97% of the papers taking a position on the cause of global warming agreed that humans are causing it.
Lead author John Cook created a short video abstract summarizing the study:
Oreskes 2004 and Peiser
A survey of all peer-reviewed abstracts on the subject 'global climate change' published between 1993 and 2003 shows that not a single paper rejected the consensus position that global warming is man caused (Oreskes 2004). 75% of the papers agreed with the consensus position while 25% made no comment either way (focused on methods or paleoclimate analysis).
Benny Peiser, a climate contrarian, repeated Oreskes' survey and claimed to have found 34 peer reviewed studies rejecting the consensus. However, an inspection of each of the 34 studies reveals most of them don't reject the consensus at all. The remaining articles in Peiser's list are editorials or letters, not peer-reviewed studies. Peiser has since retracted his criticism of Oreskes survey:
"Only [a] few abstracts explicitly reject or doubt the AGW (anthropogenic global warming) consensus which is why I have publicly withdrawn this point of my critique. [snip] I do not think anyone is questioning that we are in a period of global warming. Neither do I doubt that the overwhelming majority of climatologists is agreed that the current warming period is mostly due to human impact."
Subsequent research has confirmed this result. A survey of 3146 earth scientists asked the question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (Doran 2009). More than 90% of participants had Ph.D.s, and 7% had master’s degrees. Overall, 82% of the scientists answered yes. However, what are most interesting are responses compared to the level of expertise in climate science. Of scientists who were non-climatologists and didn't publish research, 77% answered yes. In contrast, 97.5% of climatologists who actively publish research on climate change responded yes. As the level of active research and specialization in climate science increases, so does agreement that humans are significantly changing global temperatures.
Figure 1: Response to the survey question "Do you think human activity is a significant contributing factor in changing mean global temperatures?" (Doran 2009)General public data come from a 2008 Gallup poll.
Most striking is the divide between expert climate scientists (97.4%) and the general public (58%). The paper concludes:
"It seems that the debate on the authenticity of global warming and the role played by human activity is largely nonexistent among those who understand the nuances and scientific basis of long-term climate processes. The challenge, rather, appears to be how to effectively communicate this fact to policy makers and to a public that continues to mistakenly perceive debate among scientists."
This overwhelming consensus among climate experts is confirmed by an independent study that surveys all climate scientists who have publicly signed declarations supporting or rejecting the consensus. They find between 97% to 98% of climate experts support the consensus (Anderegg 2010). Moreover, they examine the number of publications by each scientist as a measure of expertise in climate science. They find the average number of publications by unconvinced scientists (eg - skeptics) is around half the number by scientists convinced by the evidence. Not only is there a vast difference in the number of convinced versus unconvinced scientists, there is also a considerable gap in expertise between the two groups.
Figure 2: Distribution of the number of researchers convinced by the evidence of anthropogenic climate change and unconvinced by the evidence with a given number of total climate publications (Anderegg 2010).
The Vision Prize is an online poll of scientists about climate risk. It is an impartial and independent research platform for incentivized polling of experts on important scientific issues that are relevant to policymakers. In addition to assessing the views of scientists, Vision Prize asked its expert participants to predict the views of their scientific colleagues. The participant affiliations and fields are illustrated in Figure 3.
Figure 3: Vision Prize participant affiliations and fields
As this figure shows, the majority (~85%) of participants are academics, and approximately half of all participants are Earth Scientists. Thus the average climate science expertise of the participants is quite good.
Approximately 90% of participants responded that human activity has had a primary influence over global temperatures over the past 250 years, with the other 10% answering that it has been a secondary cause, and none answering either that humans have had no influence or that temperatures have not increased. Note also that the participants expected less than 80% to peg humans as the primary cause, and a few percent to say humans have no influence - the consensus was significantly better than the participants anticipated (Figure 4).
Figure 4: Vision Prize answers and expected distribution to the question "What influence has human activity had on global average ocean temperatures in the last 250 years?"
Scientific organizations endorsing the consensus
The following scientific organizations endorse the consensus position that "most of the global warming in recent decades can be attributed to human activities":
The Academies of Science from 80 different countries all endorse the consensus.
13 countries have signed a joint statement endorsing the consensus position:
- Academia Brasiliera de Ciencias (Brazil)
- Royal Society of Canada
- Chinese Academy of Sciences
- Academie des Sciences (France)
- Deutsche Akademie der Naturforscher Leopoldina (Germany)
- Indian National Science Academy
- Accademia dei Lincei (Italy)
- Science Council of Japan
- Academia Mexicana de Ciencias (Mexico)
- Russian Academy of Sciences
- Academy of Science of South Africa
- Royal Society (United Kingdom)
- National Academy of Sciences (USA) (12 Mar 2009 news release)
A letter from 18 scientific organizations to US Congress states:
"Observations throughout the world make it clear that climate change is occurring, and rigorous scientific research demonstrates that the greenhouse gases emitted by human activities are the primary driver. These conclusions are based on multiple independent lines of evidence, and contrary assertions are inconsistent with an objective assessment of the vast body of peer-reviewed science."
The consensus is also endorsed by a Joint statement by the Network of African Science Academies (NASAC), including the following bodies:
African Academy of Sciences
Cameroon Academy of Sciences
Ghana Academy of Arts and Sciences
Kenya National Academy of Sciences
Madagascar's National Academy of Arts, Letters and Sciences
Nigerian Academy of Sciences
l'Académie des Sciences et Techniques du Sénégal
Uganda National Academy of Sciences
Academy of Science of South Africa
Tanzania Academy of Sciences
Zimbabwe Academy of Sciences
Zambia Academy of Sciences
Sudan Academy of Sciences
Other Academies of Sciences that endorse the consensus:
Update January 28, 2017:
Some broken links were updated in the rebuttal. In addition, please check out the recent article Joint Statements on Climate Change from National Academies of Science Around the World published by Peter Gleick on his Significant Figures blog.
Last updated on 29 January 2017 by dana1981. View Archives
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