Note: the discussion of the Cook et al. (2013) study in this post is adapted from a CERES-science post and was co-written with our colleague, Dr. Willie Soon, who was a co-author of the Legates et al. (2015) study mentioned.
Introduction
Since the 1990s, it has been insisted by advocates for major and urgent “climate action”, i.e., the urgent reduction in carbon dioxide (CO2) emissions, that the scientific community agrees with them. From a public relations perspective, it is understandable that they would try to make this claim. If you are trying to convince the public to radically change societies and economies because of a scientific hypothesis, then it is extra hard if the hypothesis is disputed by many scientists with relevant expertise.
However, anybody can make a claim. It doesn’t make it true.
While some people were happy to accept the claim without any evidence, many in the public (and the scientific community) complained that the claim was just an assertion.
For that reason, there has been a lot of effort made to support the claim with various studies and declarations that seem impressively convincing.
These efforts seem to have worked in that many people now believe that something like 95% or 97% of scientists agree with the “climate action” advocates. As a result, anybody who disagrees is automatically assumed to be an outlier who can probably be dismissed.
However, as we will discuss in this post, each of these claims involves either (a) “loosening” the definition of what “agreeing” means and/or (b) the deliberate exclusion or suppression of dissenting opinions.
To clarify, there definitely are a lot of scientists who believe that recent climate change is mostly human-caused. And quite a few of those agree with the advocates that major and urgent “climate action” is necessary. But, there are also a lot of scientists who believe that recent climate change is mostly natural or that it has been a mixture of human and natural factors. Similarly, quite a few of these would completely disagree with the advocates. That is, there is a wide range of scientific opinions on what the causes of recent climate change are.
This is important because the claims that major “climate action” is urgently required explicitly assume that recent climate change is mostly (or entirely) human-caused from greenhouse gas emissions. And that future climate change will become catastrophic unless greenhouse gas emissions are dramatically curtailed.
The idea that there could be such a range of different scientific opinions on a subject like this may be surprising to many people, especially those without scientific training. Many non-scientists assume that the scientific process is a linear one, and is always moving forward. That is, once scientists come up with an answer, their job is done and they can move on to the next problem. The reality is a lot messier. Unlike common sense, science is non-intuitive. Scientists analyzing the same data often come to different conclusions. Also, as we get new data and insights, we are constantly revising our previous understanding.
If you want to learn more about why different scientists have different views on the causes of recent climate change, you might find our earlier post, “Is there a scientific consensus on global warming?” helpful.
However, in this section, we will dig into the various “95% of scientists” claims and see what they actually say about scientific opinion on climate change.
A short note on the use of 95%, 96%, 97% and similar numbers
As we discussed in Section 4 of our 2018 “Analysis of Greenpeace’s business model & philosophy” report (pdf here), numbers in the range 90% to 98% are very effective from a campaigning perspective.
If the number is greater than 90%, most people think, “basically everyone”. But, because it is less than 100%, e.g., 97%, then it allows you the wriggle room that if somebody voices an objection, they can be dismissed as, “they’re probably just in the 3% outliers”.
Therefore, the studies and declarations which seem the most popular tend to be ones that include percentages in the range of 90-98% as part of their claim. However, as we will see for the various climate change “95%” claims, this is typically achieved by misrepresentation of the real data.
The various “95% scientific certainty” claims
The various claims that there is 95% agreement among scientists on climate change can be broadly divided into 4 types:
- 90-95% of scientists agree on climate change
- 97% of scientific papers agree on climate change
- The UN IPCC is 95% confident that recent climate change is mostly human-caused.
- Prestigious scientific academies and societies agree on climate change.
Below, we will look at each of these types in turn.
Claim 1: “90-95% of scientists agree on climate change”
In recent years, a number of studies have found that 90-95% of scientists agree that the climate changes and/or that global temperatures are warmer now than in the late 19th century. This result seems to be quite well replicated.
For the record, we also agree with both of those statements. That is, as we mentioned in the title of this post, “95% of scientists, including us, agree that the climate is changing”.
However, these same studies are widely misinterpreted by political activists and advocacy groups to imply that 90-95% of scientists also agree with the specific claim that recent climate change is mostly human-caused, and that anybody who questions this claim is anti-science.
This has worrying implications for the scientific community, as it actively discourages scientific inquiry into the important scientific problem of “climate change attribution”.
However, as we will see, a careful inspection of the results of these surveys reveals that it is false.
Below are some of the main surveys of scientific communities on their opinions on climate change:
- Brown et al. (2008) [Survey published as guest post on Prof. Pielke Sr.’s blog here]
- Doran and Zimmerman (2009) [Open access].
- Farnsworth and Lichter (2012) [Abstract; Google Scholar].
- Lefsrud & Meyer (2012) [Open access]
- Bray & von Storch (2014) [HZG REPORT 2014-4]
- Stenhouse et al. (2014) [Open access]
- Verheggen et al. (2014) [Open access]
As can be seen from the figure below, of those surveys that asked whether “climate changes” and/or that there has been some “global warming”, all of them confirmed that at least 90-95% of scientists agree:
Indeed, of the small percentage who didn’t answer “Yes”, a substantial fraction replied “Don’t know”. So, it is true that there is an overwhelming scientific consensus, “that there has been recent climate change/global warming”.
But, when the respondents are asked on whether this climate change/global warming is mostly human-caused or mostly natural, there are a wide range of opinions. See the figure below for the exact breakdown:
This breakdown is the exact opposite of a “scientific consensus”. Therefore, some people have applied “spin techniques” in order to re-create the claims of greater than 90% agreement.
For example, by excluding the “don’t knows” and by grouping together all of the categories except for “entirely natural”, then you can make it seem like there is a “scientific consensus”.
E.g., for Farnsworth & Lichter (2012), you could technically claim, “Of U.S. climate scientists who expressed an opinion, 95% agreed that human activities played a role in recent climate change”.
However, this is misleading. You could equally as well apply the reverse logic and claim, “Of U.S. climate scientists who expressed an opinion, 75% agreed that natural factors played a role in recent climate change”.
The more honest and informative description of the data would be to say, “while 90-95% of scientists agree that there has been recent climate change/global warming, there is a wide range of opinions among the scientific community as to how much has been due to natural factors and how much was human-caused”.
Claim 2: “97% of scientific publications agree global warming is human-caused”
The Cook et al. (2013) [Open access] study was not a survey of the scientific community. But, it has also been widely cited as proof of a “97% scientific consensus” that recent global warming is “mostly human-caused”.
In the Cook et al. (2013) study, the authors examined nearly 12,000 abstracts of papers containing the keywords “global climate change” or “global warming”. The “abstract” of a scientific paper is a short summary (typically 200-300 words) of the key findings of the paper. It is provided at the start of the paper and allows scientists to quickly decide whether it is worth reading the entire paper.
Cook et al. sorted the abstracts into 7 categories depending on what position the abstract implied on the human contribution.
Cook et al. (2013) implied that 97.1% of the abstracts agreed “that human activity is very likely causing most of the current [global warming]”.
The claims of this particular study gained huge traction around the world. It seemed to provide definitive evidence once and for all that there is a single scientific consensus that climate change is mostly human-caused, and due to greenhouse gas emissions, chiefly carbon dioxide (CO2).
A number of science communicators who believe in this claim have put a huge effort into convincing the public that they are right, and that any scientist who disagrees is untrustworthy. This mission of convincing the public that 97% of scientists agree on climate change is often referred to as “Climate Change Communication”. Indeed, the lead author of that study, John Cook, currently works at the Center for Climate Change Communication at George Mason University.
If you believe this claim, then it can make you very confident and assertive in your views. This confidence can make your arguments seem very compelling.
However, let us look in detail at what the Cook et al. (2013) study actually found.
In 2015, Legates et al. (2015) [Abstract; Google Scholar] re-analysed the Cook et al. (2013) results. They showed that Cook et al. had only found 0.5% of the abstracts to have explicitly made that claim.
They had found that two thirds of the abstracts had provided no position on whether global warming is mostly human-caused or mostly natural, and only 8% of the abstracts had explicitly stated any opinion on this issue. See the figure below for the exact breakdown:
When you think about it, this is not really too surprising. Most studies looking at climate change are looking at some particular aspect of climate change, and so they aren’t going to mention anything about the causes of climate change in the short 200-300 word abstract. Instead, the abstract will focus on the key findings of the paper.
Indeed, Cook et al. conceded in their paper that 67% of the abstracts “expressed no position”.
Nonetheless, they still insisted that most of the rest agreed with their claim that global warming is human-caused (“anthropogenic”).
However, of the 8% of abstracts which made an explicit claim on the human contribution, the vast majority (91%) apparently did not offer any opinion on whether recent global warming is mostly human-caused or mostly natural. Instead, they just stated that at least some of the global warming is human-caused.
According to the Cook et al. (2013) results, only 88 of the 11,944 abstracts explicitly stated whether global warming was mostly human-caused or mostly natural. 64 claimed it was mostly human-caused and 24 claimed it was mostly natural. See below for the exact breakdown:
Moreover, when Legates et al. (2015) re-analysed the abstracts themselves they found that even these figures were unreliable. They found that only 41 of the 64 abstracts which Cook et al. had rated as “mostly human” had explicitly made that claim. They also identified several abstracts which Cook et al. had mistakenly not included in the “mostly natural” categories.
From the pie chart above, we can see that, yes, according to Cook et al.’s analysis, only 3% of the 922 abstracts that explicitly offered an opinion on the causes of global warming stated that it was “mostly natural”. Therefore, if you wanted to be misleading, you could subtract this 3% from 100% and (misleadingly!) imply that the remaining “97% of abstracts agree that global warming is human-caused”.
But, by the same logic, you could equally (misleadingly!) claim, “94% of abstracts agree that global warming is natural”.
Both claims are misleading.
A more scientific description of Cook et al. (2013)’s findings is:
- Only 88 of the 11,944 abstracts (0.7%) explicitly stated whether global warming was mostly human-caused or mostly natural. Of those, 73% chose “mostly human-caused” while 27% chose “mostly natural”.
- Meanwhile, if Legates et al. (2015)’s re-analysis is correct, then only 65 of the 11,944 abstracts (0.5%) explicitly stated whether global warming was mostly human-caused or mostly natural. Of those, 63% chose “mostly human-caused” while 37% chose “mostly natural”.
At any rate, Cook et al. (2013)’s widely-cited claims of “a 97% scientific consensus” on climate change attribution are completely unjustified.
Claim 3: “The UN IPCC is more than 95% confident that recent climate change is mostly human-caused”
We have written elsewhere on this website about the problems with the UN Intergovernmental Panel on Climate Change (IPCC)’s “attribution” statement that, “It is extremely likely [more than 95% likely] that human influence has been the dominant cause of the observed warming since the mid-20th century.”
Therefore, we won’t discuss the problems with this claim in detail here. However, if you are interested in this particular claim, we recommend reading two of our earlier posts.
- In our 2014 post, “What does the IPCC say?”, we show that, although technically 1000s of scientists are involved in the writing of the IPCC reports, the IPCC structure is very hierarchical and designed to ensure that only a small minority of the authors can pick and choose which studies and arguments will make it into the final report. The contributions of any IPCC scientists who disagree with these lead authors are routinely downplayed or even deleted.
- In our 2021 post (originally published on Medium.com in 2019), “How the UN’s climate change panel created a “scientific consensus” on global warming” we focused specifically on the various “attribution” statements of each report. We showed how the scientific arguments made by each IPCC report to support their “attribution” statement were directly contradicted by published scientific studies, and quietly dropped and replaced with completely different arguments in the subsequent reports.
Claim 4: “Many prestigious scientific societies and academies agree on climate change”
Over the years, a number of highly respected and well-established scientific societies, academies and organisations have issued statements on climate change that appear to endorse the claim that recent climate change is mostly (or entirely) human-caused; due to CO2 emissions; and that urgent “climate action” is required.
The societies will typically focus on a particular branch of science, e.g., geology or physics or meteorology. Often these societies include tens of thousands of members and their membership includes many of the most influential scientists in that branch of science. Meanwhile the academies are often multi-disciplinary but have more of a national nature, e.g., the USA’s National Academy of Sciences. They will include many of the top scientists from or working in that country.
In either case, the membership of these organisations often includes some of the most well-respected scientists in the field.
For this reason, when the organisation issues a definitive statement on climate change, many people might initially think that the statement is representative of the views of the members of the organisation. This can seem very compelling, especially when you look through the memberships of the society/academy in question.
However, invariably, when you try to find out how the membership was consulted to find out their views, it transpires that they weren’t! Instead, typically a handful of the members get together and decide between themselves that they will issue a statement on behalf of their members. Usually this is done with zero attempt to consult the membership for their actual views. Below, we will consider five examples of this.
The American Geophysical Union (AGU)’s statements
In 2013, the American Geophysical Union (AGU) issued a statement on climate change that appeared to agree with the climate action advocates. The AGU consists of more than 60,000 scientists from 144 countries. So, this initially sounds remarkably impressive. However, these 60,000+ scientists were not consulted in the drafting of the statement. Instead, the statement was written by a panel of just 14 scientists. Moreover, one of the 14 scientists later described how the panel were pressured to produce a one-sided statement and discussion of dissenting scientific opinions was discouraged:
“… [W]e were tasked to report on the most important aspects of climate change. This was incompletely done in the Statement, where they inaccurately, in my view, discuss a view of climate change that is dominated by the emission of CO2 and a few other greenhouse gases. Indeed, the Committee, under the direction of Jerry North, with the report writing subgroup led by Susan Hassol, was clearly motivated to produce a Statement of this one particular view. Under his leadership, other views were never given an adequate opportunity to be discussed.” – Prof. Roger Pielke Sr., one of the 14 scientists involved in the drafting of the AGU’s 2013 position on climate change describing the process (May 10, 2013)
The American Meteorological Society (AMS)’s statements
The American Meteorological Society (AMS) issued a statement on climate change in 2012, asserting that global warming was mostly human-caused, due to greenhouse gas emissions (see here). Since the AMS has nearly 12,000 members, this initially sounds like an impressive endorsement of the claims of the “climate action” advocates.
However, again, the statement was not obtained by consulting the members. In fact, a survey of 1812 AMS members the same year revealed that they were split roughly 50:50 on whether global warming was mostly human-caused or not (see here).
The UK’s Royal Society’s statements
The UK’s Royal Society describes itself as “a self-governing Fellowship made up of the most eminent scientists, engineers and technologists from the UK and the Commonwealth”. A maximum of only 52 new Fellows can be appointed each year, and these new members have to be elected by the existing Fellowship.
In 2007, they issued a pamphlet, called “Climate change controversies”, which insisted that eight specific scientific arguments that had been made by scientists disagreeing with parts of the IPCC reports were all “misleading”. Further, they claimed that scientists who were making those arguments were “seek[ing] to distort and undermine the science of climate change and deny the seriousness of the potential consequences of global warming”.
The pamphlet appears to have been written to undermine some of the arguments that had been made in a popular documentary that had aired in the UK that year called, “The Great Global Warming Swindle”:
The documentary was clearly polemical, but openly so. The makers of the program were arguing that media coverage of climate change was selectively only presenting one side of the science, and it was important to let the public know that there were many scientists who disagreed with the media’s narrative. It included interviews with multiple scientists who were making scientific arguments (including the eight which the pamphlet claimed to have disproved).
But, if the Royal Society had collectively “debunked” those arguments, this would have convinced many in the UK to dismiss the arguments made by the scientists in that documentary as misleading and distortion. Therefore, the pamphlet was a great boon for those who disagreed with the documentary.
However, again, the vast majority of the fellows in the society were not consulted. Instead, the entire pamphlet was written by a small panel that was apparently co-ordinated to use the prestige of the Royal Society to discredit the documentary.
Indeed, in 2010, 43 Fellows of the Royal Society signed an open letter complaining that the pamphlet did not reflect their views (see here).
The Geological Society of London’s statements
The Geological Society of London (GSL) was founded in 1807 and is the oldest geological society in the world, with more than 12,000 members.
So, when they issued a position statement in 2010 (updated in 2013) that concluded that, “CO2 is a major modifier of the climate system, and that human activities are responsible for recent warming.” (see here), it might have appeared that the GSL as a whole agreed that recent climate change is mostly (or even entirely) due to human-caused CO2 emissions.
But, again, this statement was not written by consulting the GSL members. Rather, it was written by a panel of just 10 members. A few years later, in 2018, when the position statement came under renewed discussion on the internet, it prompted a group of 33 current and former fellows of the Geological Society of London (GSL) to write an open letter to their president criticising the fact that this 2010/2013 statement did not reflect their scientific views on climate change (see here)
The American Physical Society (APS)’s statements
The American Physical Society (APS) has issued several position statements on climate change which were so strongly opposed by some that they prompted several high profile resignations from long-term members, e.g., Hal Lewis or Nobel Laureate, Ivar Giaver, and open criticism from other members (e.g., see here), including a member of the Executive Committee of the APS’ “Topical Group on the Physics of Climate” (see here).
Conclusions
The popular perception of science among non-scientists seems to be that if you are a scientist and you “do science” to answer a scientific question, then a single “scientific answer” is revealed. This fits into the “Hollywood” notion of scientists that we see in movies and TV series. That is, when the heroes in the story need a scientific answer, “the scientists” don their white lab coats and go into the lab to “do science”. After spending hours or days looking under the microscope or using some fancy expensive technology, they find “the scientific answer”.
The implication is that when scientists study a problem they all find the same answer.
However, science doesn’t actually work like that. Different scientists can come to different conclusions even from analysing the same data. And when it comes to a challenging subject like understanding the causes of climate change, there are many different types of data that a scientist might choose to analyse.
Photo of a scientist using a microscope by “Stesoares” (27 April 2018). Taken from Wikimedia Commons, CC-BY-SA-4.0.
Nonetheless, advocates for urgent climate action have taken advantage of this public perception that for every scientific question there is only one scientific answer and all other answers are non-scientific. They have then insisted that, when it comes to climate change, there is an overwhelming scientific consensus of 90-95% of scientists. And this alleged scientific consensus is that recent climate change/global warming is mostly human-caused, and specifically due to greenhouse gas emissions – chiefly, carbon dioxide (CO2).
But, as we showed in this post, this assertion is false.
- It is true that 90-95% of scientists agree that there has been recent climate change/global warming. We would be included in that 90-95% of scientists.
- However, there is a wide range of opinions among the scientific community as to how much of that climate change was natural or human-caused in origin.
