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Debunking New Myths about the 97% Expert Consensus on Human-Caused Global Warming

Posted on 17 July 2013 by dana1981

This post has been incorporated into the rebuttal to the myth "97% consensus on human-caused global warming has been widely discredited and misclassified 35% of abstracts"

A survey of over 12,000 peer-reviewed climate science papers by our citizen science team at Skeptical Science found a 97% consensus among papers taking a position on the cause of global warming in the peer-reviewed literature that humans are responsible.  Not surprisingly, our results have been subject to attacks from those who would prefer to continue to deny the reality of the expert consensus on human-caused global warming.

For example, on Sunday July 14th, 2013, Andrew Neil hosted UK Energy and Climate Change Secretary Ed Davey on the BBC show Sunday Politics.  Rather than discussing politics, Neil began the show by misrepresenting our consensus paper, making several false statements about it within the first 2 minutes of the show.

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Neil has requested that people provide him with examples of the factual errors in this interview, and given that he began with errors in discussing our paper, we are happy to oblige.  Here are his erroneous comments about our study:

"That [97% consensus] survey has of course been substantially discredited ... 35 percent of the abstracts were misclassified, and they were classified to the pro-global warming side.  Professor Richard Tol ... has disassociated himself from that and said it's not reliable."

All of Neil's claims here refer to comments economist Richard Tol has made about our paper on his personal blog.  He submitted those comments to the journal that published our paper, Environmental Research Letters, whose editor promptly rejected it.  The editor noted that in addition to being "written in a rather opinionated style" and reading "more like a blog post than a scientific comment," "I do not see that the submission has identified any clear errors in the Cook et al. paper that would call its conclusions into question."

The claim that we "misclassified" 35 percent of abstracts is simply based on Tol's preference that a survey like ours be less precise and more general.  Our team read and categorized every abstract based on what it said about the causes of global warming, whereas Tol believes that every paper discussing the impacts of climate change should be placed in the 'no opinion' category.  We classified these abstracts correctly based on the categories established in our study.  Tol believes the categories should be defined differently, and he is free to repeat our study with whatever categories he would like, but the claim that we misclassified these papers is factually wrong.  Let's take one example:

"Humans are engaged in an uncontrolled experiment in planetary heating. Each decade, the concentration of CO2, methane and other greenhouse gases in the atmosphere is increasing by about 4%. All signs point toward unprecedented rates of warming and climate change." (Soule 1992)

In our survey, we classified this paper as an explicit endorsement of human-caused global warming.  According to his categorization, Tol would have to classify it as 'no opinion'.  You be the judge as to who's misclassifying abstracts.

Additionally, we didn't just rely on our abstract ratings.  In a second phase of our study, we invited the scientists to rate their own complete papers.  When we compared our abstract ratings to the author self-ratings based on the full papers, contrary to Neil's claim, we found that we had classified them more in the 'no opinion' category and less in the pro-human caused global warming categories than the authors themselves.

Histogram of Abstract Rating (expressed in percentages) minus Self-Rating. 1 = Explicit endorsement with quantification, 4 = No Expressed Position, 7 = Explicit rejection with quantification. Green bars are where self-ratings have a higher level of endorsement of AGW than the abstract rating. Red bars are where self-ratings have a lower level of endorsement of AGW than the abstract rating.

Regarding Neil's claim that Tol has disassociated himself from our study: Tol has never been associated with the analysis of our study.  He was one of 29,083 authors of articles that we examined, and one of 1,200 authors who participated in the self-rating phase. So the statement that he has disassociated himself is meaningless.  His opinions about how his own papers should be categorized are included in the 97 percent consensus in self-rated papers.

Those author self-ratings are a key component of our study and conclusions.  In both the abstract ratings and author self-ratings, we found the same 97 percent consensus result.  Tol has only criticized the abstract ratings survey; even if you disregard those results, the 97 percent self-ratings consensus remains.

consensus over time

Percentage of papers endorsing the consensus among only papers that express a position endorsing or rejecting the consensus.  From Cook et al. (2013).

This is why our results remain widely accepted.  Neil's assertion that they have been "widely discredited" is simply a repetition of baseless claims made on climate contrarian blogs.  If Neil relies on contrarian blogs for his climate information, that may explain why he is woefully misinformed on the subject.

Note: Neil made a number of other false and misleading statements about global warming during this show.  For a comprehensive debunking of these, see Climate Consensus  – the 97%.

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Comments 1 to 14:

  1. Heidi Cullen points out in "The Weather of the Future" that the use of the word irreversible and uniquivocal, by the top scientists outlining our future, were accepted and expected. The situation is that serious; the right scientists know it (where does an economist learn his climate science?)*, and have given us working material to avoid disaster.


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  2. "Neil has requested that people provide him with examples of the factual errors in this interview."  How very polite of him. Yet his request is hosted on twitter which is perhaps indicative of the level of detail at which he deals with climate change. And due to the restriction to 140 characters or less, I'm unable to link to a graphical example of his "factual errors" because of the infeasibly long URLs used by google.

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  3. MA Roger: tell him about URL shorteners.

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  4. Neil refers to a study by Hans Von Storch and also quotes him. Can anyone enlighten me as to who Hans Von Storch is? Thanks.

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  5. It's amazing how many times in this interview Ed points out in the simple words that climate sicence is not only about land temperatures but Andrew goes back to his imaginary "plateau" in XXI century because it's very "intriguing". Every time, he denies every point he hears.

    Ed would heve done better job saying that we know the physical mechanisms behind the "plateaus" such as the XXi century's one (recal the SkS's escalator to prove there were many of those) with ElNino/LaNina episodes acting as heat exchangers between Ocean (the main heat energy reservoir  - 90%) and Athmosphere (which holds only small fraction of heat enrgy - therefore the exchange resulting in wider swings of temperature). But I don't think that argument would make any impression on Andrew: like all other arguments, he would simply ignore it.

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  6. Being from the U.S. I am unfamiliar with Andrew Neil,but I have to say that I am very put off by his type of interview style,which has become so common these days,where he asks a question,and then proceeds to step on the answer given,in mid-sentence,and then refuses to let the interviewee complete their thought.Also the agressive bulldozing assertion of 'facts' without giving the other side a chance to rebut without,again,interrupting is both rude and frustrating for those whom actually want to hear what the person has to say.

    The whole process is clearly being proffered more as a sort of boxing match to be won,rather than a forum to enlighten,educate,and discuss one of the most important issues that mankind has ever faced.That is truly shameful,cynical,and disgusting!

    By the way,Ed Davey did  remarkably well  under the circumstances,and he seemed spot on with his facts,so good job to him!

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  7. Zen @4, Hans von Storch is a german climate scientist who has an unfortunate tendency to portray differences of opinion with other scientists as to just how harmful global warming will be in terms of the other scientists "over selling" the dangers. He, along with Dennis Bray, he has published the most interesting and detailed survey of climate scientist's opinions on climate science.

    Unfortunately, the survey has (at least) one major technical flaw. Many of the questions are phrased as "How convinced are you that ...", which choices listed from "not at all convinced" (1) to "very much convinced". Technically, anybody who is a little convinced that the statement is not true, or has no opinion on the matter would be "not at all convinced" under this scheme. Thus, anybody responding "2" or higher at least thinks the statement is more likely true than not. Certainly somebody responding "4", ie, that they are moderately convinced are not epistemically neutral on that issue.

    Bray and von Storch, and likely most respondents have interpreted questions with that format as representing a range of opinion from complete disagreement to complete agreement with "4" representing a neutral response. They have done this based on normal conventions in survey responses which tend to over ride strict interpretation of questions. The result is that the survey response is, IMO, biased against agreement on various issues.

    Despite this, on the crucial questions, "20. How convinced are you that climate change, whether natural or anthropogenic, is occurring now?", and "21. How convinced are you that most of recent or near future climate change is, or will be, a result of anthropogenic causes?" (both on page 46), climate scientists overwhelmingly support the consensus responses. In the first case, the mean response is 6.4 with a standard deviation of approximately 1, and a total of 93.8% "agreeing", ie, having a response of "5" or higher. In the second case, the mean response is 5.7 (st dev = 1.4), with 83.5% "agreeing".

    The discrepancy between the 83.5% figure from Bray and van Storch (2010) and Cook et al 2013 is partly due to the bias discussed above, and partly because they survey different things. Specifically, Cook et al survey the proportion of scientific papers endorsing the consensus while Bray and von Storch directly survey the opinions of scientists. From Anderegg et al, we know that scientists "convinced by the evidence" in favour of the consensus have, on average, published twice as many peer reviewed articles as those who are "unconvinced by the evidence". On that basis alone, even accepting Bray and Von Storch as accurate, we would expect 91% of papers to endorse the consensus. Further, the evidence simply does support the consensus. Consequently those who are less convinced, if accurately reporting the evidence, will less frequently be able to find results that actually endorse their beliefs. There will be a tension between their beliefs, and the evidence that will be reflected in the literature.

    Given this, Bray and von Storch (2010) does not rebut, or call into question the results of Cook et al (2013). What it does do, or should do, is put a brake on the misinterpretation of Cook et al as showing that 97% of climate scientists endorse the consensus. Cook et al does not show that, and cannot show that because it is a survey of the literature, not of scientists opinions.

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  8. But Neil has repeated the "skeptic" mantra of climate science being "discredited".  The people who want to believe this will accept it uncritically.  Some members of the the public will be influenced as well.

    But the "skeptics" continued bleating will in the end discredit them.

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  9. Andrew Neil was once editor of Britain's Sunday Times, with proprietor one Rupert Murdoch. Neil owed his big break to Murdoch, and it was the start of his "distringuished" media career.

    Enough said?

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  10. Tom - Thanks for the info.

    I was wondering what peolple think about the quote from Von Storch where he states that, if things continue as they are for another 5 years, then climate scientists will have to fundamentally acknowledge there is something wrong with their models?

    I have complained to the BBC about the way Neil conducted the interview; here is a link for anyone who wishes to do the same.

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  11. Zen @10, I prefer to not comment on quotes from climate scientists unless I can see the full quote in context, with a link to the original source.

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  12. Tom and Zen, the quote is from an interview in Der Spiegel.

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  13. Ian Forrester @12, thank you.  I had in fact found that interview already, but do not consider it sufficient context.  In particular, von Storch bases his views on a series of model runs he performed at the University of Hamburg.  He does not indicate of the research has been published so that there is, on public record, sufficient information to critically examine his claims.

    He does not indicate whether his results were based on a HadCRUT4 mask, so that it did not include data from rapidly warming Arctic regions that are excluded from HadCRUT4. 

    He does not indicate wether or not the model he used generates ENSO like fluctuations in the Pacific, and so whether or not it incorporates the major source of natural short term variability.  I took the data for the Southern Oscillation Index, inverted it and normalized it to the HadCURT4 temperature record, thus giving a reasonable prediction of what global temperatures would be doing absent any forcing.  The resulting trend was -0.05 C equivalent per decade.  Adjusting the HadCRUT4 data to eliminate that negative trend results in a warming trend of 0.139 C per decade which is statistically significant.  The point here is without accounting for the effects of the ENSO oscilation it is impossible to understand the current "pause" in temperature increases, and no model that does not emulate those oscilations can hope to correctly assess the probability of 15 year "pauses".  

    Nor does he indicate which set of forcings he uses.  For example, the lates GISS forcing data shows a near zero trend in forcings over the early twentieth century, in large part due to a transition from a solar maximum to a solar minimum:

    Does the Hamburg model really only show 15 year "pauses" in warming only 2% of the time during periods in which there is a 15 year "pause" in the increase in forcings?  Or have they merely used forcing data that does not accurately reflect actual forcings over the last decade?

    Finally, he does not even indicate whether they defined "stagnation" as zero trend, or a trend statistically indistinguishable from zero.  The current "pause" in temperature increase exhibits the later, but not the former.  If it is defined as the former, he has misrepresented the applicability of his research to the current temperature data.  If the later, again I find it incredible that they would only find a trend of 0.12 C per decade or less just 2% of the time.

    There may be more substance to von Storch's claims than I would credit given the background knowledge I have.  It looks, however, unlikely.  The research may be quite fine and above board, and totally inapplicable because it does not model appropriate conditions.  Or the research may simply be very shoddy, coming up with incredible results.  Or I may have something to learn here.  But until the research is released I do not have enough context to say.

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  14. “For example, on Sunday July 14th, 2013, Andrew Neil hosted UK Energy and Climate Change Secretary Ed Davey on the BBC show Sunday Politics”.

    This interview was disgusting. Andrew Neil refused to “discuss” the issues. He simply pushed his opinions. He reminded me of the saying “America right or wrong.” This was simply propaganda blindly forced and ignorantly proposed: journalism at its worst.

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