Do those who doubt climate catastrophism lack scientific credibility?

Agresti, J. D. (2013, May 20). Do those who doubt climate catastrophism lack scientific credibility? Retrieved from
Agresti, James D. “Do those who doubt climate catastrophism lack scientific credibility?” Just Facts. 20 May 2013. Web. 27 March 2017.<>.
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James D. Agresti, “Do those who doubt climate catastrophism lack scientific credibility?” Just Facts. May 20, 2013.
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Agresti, James D. “Do those who doubt climate catastrophism lack scientific credibility?” Just Facts. May 20, 2013.

By James D. Agresti
May 20, 2013
Correction Appended

Heat-Trapping Gas Passes Milestone, Raising Fears,” declared a recent front page headline in the New York Times. The event that served as the catalyst for this article was the atmospheric concentration of carbon dioxide reaching 400 parts per million (ppm), up from 288 ppm or by 39% since the dawn of the industrial revolution in the mid-1800s.

Painting an ominous picture of the situation, the reporter, Justin Gillis, quoted scientists who proclaimed that:

• reaching this milestone “feels like the inevitable march toward disaster,”
• “we are quickly losing the possibility of keeping the climate below what people thought were possibly tolerable thresholds,”
• “we have failed miserably in tackling this problem,”
• “I feel like the time to do something was yesterday,” and
• “It’s scary.”

Amidst these dire assessments, Gillis quoted and quickly rebutted a lone dissenting voice to these scientists: Dana Rohrabacher, a Republican congressman from California. Simultaneously, Gillis alleged that “climate-change contrarians” have “little scientific credibility.” Based upon such reporting, one would think that no credible scientist doubts that manmade global warming is a grave threat to the future of the planet.

That narrative, however, is at odds with the fact that 3,805 scientists with degrees in atmospheric, earth, or environmental science and 9,029 Ph.D.’s in varying scientific fields have signed a petition stating, “There is no convincing scientific evidence that human release of greenhouse gasses is causing or will, in the foreseeable future, cause catastrophic heating of the Earth’s atmosphere and disruption of the Earth’s climate.”

In this article, Gillis made no attempt to support his allegation that “climate contrarians” have “little scientific credibility,” but in reply to an email from Just Facts, he referred to “the Anderegg study and several more.” These studies, however, do not substantiate his storyline. At best, they show that the most frequently published climate scientists think the earth has warmed over the past century, and human activity is responsible for most of this warming. Furthermore, even those relatively modest conclusions are undermined by significant flaws in the studies.

The Anderegg study

In 2010, the Proceedings of the National Academy of Sciences published a study by Bill Anderegg and others entitled “Expert credibility in climate change.” For this study, the authors compared the scientific expertise of 1,372 climate researchers that they labeled as either “convinced by the evidence” for manmade global warming or “unconvinced by the evidence.”

They defined “convinced” researchers as those who embrace the views that manmade “greenhouse gases have been responsible for ‘most’ of the ‘unequivocal’ warming of the Earth’s average global temperature over the second half of the 20th century.” Those words are paraphrased from a massive 2007 report on the science of climate change by the Intergovernmental Panel on Climate Change (IPCC).

The Anderegg study found that more than 90% of “convinced” researchers had at least 20 publications listed in Google Scholar under a search for the word “climate,” as compared to only 20% of “unconvinced” researchers. They also found that among those with at least 20 publications, convinced researchers had an average of 119 climate publications in Google Scholar, as compared to an average of 60 publications for unconvinced researchers.

If one uncritically accepts the results of this study, it shows clear numerical superiority in Google Scholar for convinced researchers, but this is a far cry from Gillis’ claim that “climate contrarians” have “little scientific credibility.” There are numerous Ph.D. scientists that Gillis could have cited in opposition to the scientists that he quoted, but instead, he selected a Republican congressman. This propagates a misleading narrative that all scientists are on one side of this issue, while Republican politicians are on the other side.

Moreover, the Anderegg study does not show that “convinced” researchers embrace the calamitous views of global warming quoted by Gillis. In fact, a number of the researchers categorized by the authors as “convinced” may not even embrace the more moderate views that the study ascribes to them. This is because the authors presumptuously assigned 619 researchers to the “convinced” category based solely on them being contributors to the above-mentioned 2007 IPCC report.

That methodology is questionable because being a contributor to this 996-page report does not necessitate accepting its conclusions. As the technical summary of the report states at the outset, “the material has not been subject to line-by-line discussion and agreement, but nevertheless presents a comprehensive, objective and balanced view of the subject matter.”

For example, John Christy, one of the authors of this report, has explicitly rejected the view that the Anderegg study attributed to the report’s contributors. As Christy explained, the IPCC report “says we are 90 percent certain that most of the warming in the last 50 years was due to human effects. I don’t agree with that. I think things are much more ambiguous.”

In addition to the IPCC report, Anderegg and company compiled their list of “convinced” researchers from four public statements about global warming that expressed clear positions on this issue. These statements were signed by 499 researchers (including duplicates). Why the authors felt the need to go beyond these people and incorporate all contributors to the 2007 IPCC report does not bode well for the study’s credibility. In short, it is highly dubious to assign views to scientists that they have not expressed.

The Anderegg study is also plagued by other issues, but this one alone is enough to call the results into question. And again, even if one blindly accepts the results, the study does not show that all credible scientists see global warming as a serious risk, which is the clear message of Gillis’ article.

The Doran study

Another frequently cited study about scientists’ views on global warming was published in Eos, “the premier international newspaper of the Earth and space sciences.” This article is entitled “Examining the Scientific Consensus on Climate Change” and was written by Peter Doran and Maggie Zimmerman of the University of Illinois. This study purports to show that “an unbiased survey of a large and broad group of Earth scientists” found that:

• 90% think average global temperatures “have generally risen” since the 1800s.
• 82% think “human activity is a significant contributing factor in changing mean global temperatures.”

The study also categorized a subgroup of respondents as “the most specialized and knowledgeable” if they reported that climate science was “their area of expertise,” and “more than 50% of their recent peer-reviewed papers” were about this subject. These stringent criteria restricted this subgroup to 2.5% of all respondents and less than 1% of the scientists who were sent the survey. Among these individuals, 96% and 97% agreed with the statements above.

Tacitly referring to this study, Gillis wrote in an April 2012 article that “polls say 97 percent of working climate scientists now see global warming as a serious risk.” As with his recent claim about “little scientific credibility,” he provided no link to substantiate this assertion. Nonetheless, this clearly references the Doran study, as evidenced by the “97 percent” figure and the prominence of this study.

Once again, Gillis stretched his reporting far beyond the study’s findings. The Doran study says absolutely nothing about global warming being a “serious risk.” Also, Gillis labeled every scientist not categorized by this study as “the most specialized and knowledgeable” as not being “working climate scientists.” In other words, he used a capricious definition of “working climate scientists” that includes only 2.5% of the scientists who responded to the survey.

This is especially problematic given that 8.5% of the scientists who responded to the survey indicated that “more than 50% of their peer-reviewed publications in the past 5 years have been on the subject of climate change.” Furthermore, there is no rational basis to assert that scientists don’t qualify as “working climate scientists” unless more than half of their papers are about climate change. It is not uncommon for scientists to have multiple areas of expertise and to be highly knowledgeable on a wide range of associated topics.

Beyond this, the Doran study has a major flaw, which is that the results are based on an internet survey that yielded a 31% response rate. The authors point out that this is “a typical response rate for Web-based surveys,” but this has no bearing upon whether the poll is credible. The issue is not how the Doran survey compares to other internet surveys but whether internet surveys are even reliable. As it turns out, internet and mail surveys often suffer from a phenomenon called selection bias or nonresponse bias, which frequently makes them untrustworthy.

Selection bias can take different forms, but for the type of poll used for the Doran study, it typically occurs because certain people are more likely to respond, specifically those who are opinionated or not very busy. As explained in the textbook Mind on Statistics, “Surveys that simply use those who respond voluntarily are sure to be biased in favor of those with strong opinions or with time on their hands.” Suitably, after stating this, the textbook analyzes a poll of scientists that had a 34% response rate, and it explains that “with only about a third of those contacted responding, it is inappropriate to generalize these findings” to most scientists.


In his recent article about CO2 levels reaching the numeric milestone of 400 ppm, New York Times environmental reporter Justin Gillis painted a picture of impending doom and casted all who differ as lacking in scientific credibility. However, thousands of Ph.D. scientists have explicitly stated there is “no convincing scientific evidence” that manmade greenhouse gases will “cause catastrophic heating of the Earth’s atmosphere and disruption of the Earth’s climate.”

Gillis has cited at least two popular studies to support his claim, but these studies don’t prove what he asserts. Instead, they show near-universal support among the most frequently published climate scientists for the more moderate views that the earth has warmed over the past century and human activity has contributed significantly to this. However, these studies have substantial flaws that cast doubt on their credibility, and thus, it is misleading to cite them without qualification.

Correction (3/10/17): The original version of this article incorrectly stated that “9,029 Ph.D. scientists, including 3,805 atmospheric, earth, and environmental scientists” signed the above-mentioned petition.” As shown in the current article, the figure of 3,805 scientists is independent of the figure of 9,029 Ph.D.’s, not a subset of it.

Additional reading:
Will global warming flood the coasts of the United States?
Activists and journalists mislead the public about carbon pollution

The Associated Press on greenhouse gases, the United States, and the Kyoto Protocol

15 thoughts on “Do those who doubt climate catastrophism lack scientific credibility?

  1. This analysis is not really fair and doesn’t take into account the latest study on the subject.

    First, interpretation of polls is a social science question, not a physical science question. The answers are never going to be absolute. At best in this case it is a proxy measurement of what scientists actually believe.

    Second, the Oregon Petition project has always had major problems. See Skeptical Science article about the Petition project..

    Third, I am somewhat familiar with the methodology of the 2009 Doran and Zimmerman study. In fact, I even wrote an article about it . I don’t think anyone would say that this survey was the final word on the subject, but it’s important to mention that the study was published in a peer reviewed journal and its methodology was explained in detail and checked by other people in the field. Not the best or most conclusive methodology, but I don’t think it claimed to be such.

    Fourth, I’m not particularly familiar with the Anderegg study, but I am very surprised you didn’t discuss the Cook/Nuccitelli survey which just came out on April, 2013. I think it made an attempt to deal with the self-selection issues you mentioned . Here’s the abstract:

    We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11 944 climate abstracts from 1991–2011 matching the topics ‘global climate change’ or ‘global warming’. We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming. In a second phase of this study, we invited authors to rate their own papers. Compared to abstract ratings, a smaller percentage of self-rated papers expressed no position on AGW (35.5%). Among self-rated papers expressing a position on AGW, 97.2% endorsed the consensus. For both abstract ratings and authors’ self-ratings, the percentage of endorsements among papers expressing a position on AGW marginally increased over time. Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research.

    What’s significant here is that three studies using separate methodologies seemed to reach similar conclusions about consensus.

    I’m sure there are scientists who deny the scientific consensus, but it’s not clear that these people are knowledgeable about climate science. From my perspective (as a layman), I think the debate has moved past the consensus question but the climate sensitivity issue — as well as the feedback loops at the poles, and the aerosol questions. And of course, the policy questions.

    As far as I am convinced, whether 97% or 85% or 60% accept that AGW exists and is a problem doesn’t really change the policy implications. If 60% or 85% or 97% say that cigarettes cause cancer, I don’t think that would imply that people shouldn’t seriously consider giving up smoking.

    • First, your link to the critique of the Oregon Petition is not credible. It was posted/updated (the website is not even clear on this) by someone who only identified himself/herself as “gpwayne.” Moreover, it is rife with blatant non sequiturs and half-truths.

      Second, the article you wrote about the Doran study begins with two patent falsehoods:

      I saw an interesting statement in the comment section of “97% of climate scientists agree that climate change is real, it’s happening now, it’s man made, and it has grave consequences.”

      This statement seemed plausible, but was unsourced, so I asked for evidence. Turns out there is recent poll data on that, and I’ll try to summarize the results.

      As documented in my article, the Doran study says absolutely nothing about climate change having “grave consequences,” and the “97%” figure does not apply to “climate scientists.” Yet, you began your article by quoting these untruths and never challenged them.

      Third, you wrote that the Doran study “was published in a peer reviewed journal and its methodology was explained in detail and checked by other people in the field.” In fact, the Doran study is a non-peer-reviewed article, not a peer-reviewed paper. This is evidenced by the format of the piece and the fact that the authors’ names appear at the end of it. This is the standard practice for non-peer-reviewed articles that appear in journals.

      Fourth, the Cook/Nuccitelli study did not come out in April as you claim. It was approved for publication in April but was not published until May 15th, which is five days after the Gillis article was published and after the bulk of my article was written. I plan to examine this study in the future.

      Finally, your entire critique misses the central point of my article: It is a provable falsehood to claim that those who doubt climate catastrophism lack scientific credibility. Nothing you wrote changes that.

      • If these studies claimed that those who doubted climate catastrophism lacked scientific credibility, then you would be correct. But the studies did not do that. They merely claimed (I’m generalizing) a strong correlation between advanced knowledge in this field and a tendency to accept the AGW thesis.

        • It was Justin Gillis of the New York Times that made that claim. This was explained several times in the article. Your comment reveals that you either don’t understand the article or are deliberately misrepresenting it.

    • The Cook/Nuccitelli survey is a joke!
      That study is subjective, and suspect to the confirmation bias of the volunteers categorizing papers they selected using a biased method. Contradicting the study’s claim, these surveyors were not independently making their conclusions either. They were discussing their findings, and changing their results.

      About the only thing this survey has shown is that 2/3rds of the papers they choose contain no position on the AGW hypothesis.

      Worse still, a follow up with some of the scientists who authored the papers categorized in the study as supporting AGW completely disagreed with that categorization. They rejected the claim their paper supported AGW! Who are we to believe? This biased study or the actual scientists?

  2. Mr. Agresti,

    The support for your conclusion is very weak, especially considering the fact that you relied primarily on a petition that was produced by an organization that has an agenda to discredit the idea that human-caused global warming is happening. I have read the Doran survey and the process for disseminating it to scientists and fully believe that it is the most effective survey that has been done so far. We need many more though. Would you start an effort to do this?

    To better support your idea, why not find some other ways to positively support your idea that these scientists ARE credible, rather than trying to discredit those who are researching and reporting on the human-caused global warming hypothesis. I must emphasize to readers that this is a common tactic of those without much material to support their view.

  3. Oddly enough, a few years ago, National Geographic published a timeline of ice core samples tested for CO2 levels corresponding to atmospheric CO2 at the time the ice was laid down. Although they were trying to emphasize human contributions to increasing global temperatures, they did have the intellectual honesty to include all the data. This showed higher CO2 levels 10,000 years ago than now. Hmmmm, not alot of internal combustion engines and Chinese coal-fired electricity plants back then. Just an observation.

  4. J. Vogus. You didn’t cite a study, and I think your timeline is wrong anyway. Perhaps the National Geographic research was referring to a local (not a global) condition.

    The last time global CO2 levels were what they are today was about 3-4 million years ago. The 2nd chart on this blogpost shows CO2 levels 10,000 years ago.

    But just because CO2 levels were higher in the past doesn’t refute the AGW thesis; in many ways historical records confirm it –see this explanation

    • Robert said, “But just because CO2 levels were higher in the past doesn’t refute the AGW thesis”

      Conversely, higher levels of CO2 today do not prove the AGW hypothesis. This is circular reasoning. The assumption is that CO2 is driving temperature. Therefore one cannot then state higher levels of CO2 are the proof of this. There is a correlation of the two, but there are a number of other significant correlations as well. One must prove the causative relationship, and the relative degree (since there are many factors contributing to global temperatures). Most importantly we must first refute the null hypothesis (natural causes).

      Before we can consider CO2 we have to first determine if the current temperatures changes in the relatively minute time frame of the past few decades are natural. Yet we’ve seen temperatures higher than today within the past 2000 years, and we’ve gone through faster warming periods too.

  5. The phrase “Climate Change” seems to have been highjacked by those believing in Anthropogenic Global Warming. The attempted merging of the two terms by global warming fanatics demonstrates their lack of interest in careful examination of the facts.

    Climate Change has been happening for ever, the world has had glacial periods and the river Thames in London used to freeze in winter several hundred years ago,

    The pretty successful supression of the fact-filled rebuttal – the Inconvenient Truth about the Inconvenient Truth – to the serious flaws of the original Inconvenient Truth film demonstrate the refusal to allow people to judge the facts and make up their own mind. The Inconvenient Truth film was declared as having serious scientific flaws by a British high court Judge. One is that it assigns colors to the CO2 levels and Temperature, which are then swopped around to mislead about which comes first. Such egregious manipulation seems typical of those attempting to equate AGW with natural, ongoing Climate Change which has been occurring for millions of years.

  6. I saw a program on the Smithonian channel that some scientists claimed the earth wobbles. Not wobbles real fast but on a 14000 year cycle. At one end of the wobble the the northern hemisphere is farther away from the the sun and after about 14000 years the northern hemisphere is closer to the sun. The program went on to say that this time frame would account for the ice ages the earth has experienced. Man may have something to do with a little warming but if these scientists findings are true let’s just get on with living because we can’t do anything about the wobble. Makes sense to me.
    Will Swoboda

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