Yet more problems with Anderegg et al “denier black list” paper

Blog, Energy, Tom Harris

In “Climate scientists’ “consensus” based on a myth” I described how one of the sources of the idea that 97% of climate experts agree there is a human-induced climate crisis—“Examining the Scientific Consensus on Climate Change” by Doran and Zimmerman—was not a meaningful indicator of  expert opinion.

The other major source of the consensus myth isExpert credibility in climate change”, the 2010 paper in the Proceedings of the National Academy of Sciences of the United States by Anderegg et al.  On December 5, the CBC cited this poll, writing:

“In 2010, a survey of more than 1,000 of the most cited and published climate scientists found that 97 per cent of them believe climate change is very likely caused by the burning of fossil fuels.”

What the network don’t know, or chose to not tell readers about, is that many articles have taken this study apart. Here are some:

One of the major problems with the Anderegg et al study has not, to my knowledge, been discussed, namely the way it selects scientists to represent the two sides of the debate.

As has already been discussed by the authors of the above articles, dividing scientists into merely two groups makes no sense in such a complex field. Many scientists agree with some elements of the climate scare while disagreeing with others. Many scientists support the idea that, while humanity’s greenhouse gas (GHG, the one most discussed being carbon dioxide) emissions are causing some warming, it is not enough to be dangerous. Other experts dispute even the existence of the “greenhouse effect”.  Many scientists, perhaps the majority of experts in the field, simply say they do not know the degree to which our GHG emissions affect climate (“Ask me in ten years!” is a common answer).

But let’s examine the way Anderegg et al derive their lists of scientists in the fictitious two camps to see if it makes sense.

  1. The “convinced of the evidence”, or “CE” camp: Anderegg et al write in their paper. “We defined CE researchers as those who signed statements broadly agreeing with or directly endorsing the primary tenets of the IPCC Fourth Assessment Report that it is “very likely” that anthropogenic greenhouse gases have been responsible for “most” of the “unequivocal” warming of the Earth’s average global temperature [sic] in the second half of the 20th century. We compiled these CE researchers comprehensively from the lists of IPCC AR4 Working Group I Contributors and four prominent scientific statements endorsing the IPCC (n = 903).”
  2. The “unconvinced of the evidence” or “UE”, camp: from the paper, “We defined UE researchers as those who have signed statements strongly dissenting from the views of the IPCC. We compiled UE names comprehensively from 12 [it was really 13] of the most prominent statements criticizing the IPCC conclusions (n = 472).”

Of course, the issue they are examining is wrong. Of concern is not whether “anthropogenic greenhouse gases have been responsible for “most” of the “unequivocal” warming of the Earth’s average global temperature [sic] in the second half of the 20th century”. The public concern is whether scientists agree that we are due for dangerous warming and other problematic climate change due to continued GHG emissions. The past is past. It is the future we should be concerned about. Several authors point out that the Anderegg et al is therefore not helpful to today’s debate.

Regardless, let’s continue with analyzing whether the Anderegg et al study accomplished what it says it did, or if it was even possible, given the populations of scientists they chose to assess.

Applying dubious filtering methods, Anderegg et al counted the number of research papers by scientists in each of the two groups (which reflects the relative climate expertise, they say), as well as the number of times they were referenced in the literature (reflecting the scientific prominence of the researchers, Anderegg et al claim). This approach showed how much more qualified CE researchers supposedly are than those in the UE camp, according to the paper authors. They did not poll anyone to get their results, it is just counting papers and citations.

As other authors have pointed out, assuming that all of the contributors to the IPCC AR4 Working Group I report (coordinating lead authors, lead authors, and contributing authors for a total of 619 names), agree with the statement in question is not substantiated. Very few of the IPCC authors would have said anything at all about the causes of the so-called ““unequivocal” warming of the Earth’s average global temperature in the second half of the 20th century”. They commented about their own specialties only, everything from sea level to ice cover to urban heat islands to the impact of aerosols on clouds. As ICSC Policy Advisory Board member John McLean of Australia and I showed in our articles (here is one), IPCC contributors’ opinions about “the primary tenets of the IPCC Fourth Assessment Report” is known for only a very small fraction of them. So assuming they are all CE scientists seriously inflates that camp’s numbers.

The data source Anderegg et al used for the skeptics, the UE population, and their codes for each source, is as follows:

  1. APS09: 2009 letter to the American Physical Society, 61 signers: Skeptics letter to the APS (Google cache)
  2. NIPCC09: 2009 Heartland Institute document, Climate Change Reconsidered: 2009 Report of the Nongovernmental Panel on Climate Change (NIPCC), Craig Idso and S. Fred Singer, eds.; 36 contributors listed: NIPCC 2009 full report – front matter listing contributors
  3. Cato09: 2009 Cato Institute newspaper ad campaign letter; 115 signers: Text of 2009 Cato climate ad
  4. MHND2008 ‘Manhattan Declaration’ – list of 206 signers identified as qualified experts (endorsements from non-experts, listed separately, are not addressed by Anderegg et al) Manhattan Declaration
  5. NIPCC08: 2008 SEPP/Heartland Institute document Nature, Not Human Activity, Rules the Climate: Summary for Policymakers of the Report of the Nongovernmental International Panel on Climate Change, ed. S. Fred Singer, 24 listed contributors: NIPCC 2008 S.P.M.
  6. UN07: 2007 letter to UN Secretary General Ban Ki-Moon, 100 signers: climate skeptics letter to Ban Ki-Moon
  7. ISPM07: 2007 “Independent Summary for Policymakers” questioning the IPCC AR4: list of 10 authors
  8. TGGWS: 2007 Martin Durkin film The Great Global Warming Swindle – list of 17 interviewees
  9. CA06: 2006 open letter to Canadian PM Stephen Harper, 61 signers: 2006 skeptics letter to Cdn. PM Harper
  10. CA03: 2003 open letter to Canadian PM Paul Martin, 46 signers: 2003 skeptics letter to Cdn. PM Martin
  11. CA02: 2002 letter to Canadian PM Jean Chretien, 30 signers: 2002 skeptics letter to Cdn. PM Chretien. In the absence of an online copy of the original, here is a cached copy of the list of signers, with their affiliations, as given in the letter.
  12. LZ95: 1995 Leipzig Declaration, 80 signers all listed (additional 25 TV weather reporters not counted): Leipzig Declaration
  13. SEPP92: 1992 SEPP Statement by Atmospheric Scientists on Greenhouse Warming, 47 signers (all listed): SEPP 1992 statement on greenhouse warming

One of the Anderegg et al co-authors, James W. Prall of the Electrical and Computer Engineering at the University of Toronto writes on his Website:

“I assert that this [the above list] yields a broadly inclusive list that captures the great majority of those contrarians presenting themselves as qualified experts or specialists in climate science or related disciplines.”

As a participant in the writing and endorser collection for about half of the above documents from the UE crowd, I have first hand experience of how un-inclusive these lists actually are. It is not that we refused to include qualified scientists who wanted to endorse the lists. It’s that, every project I was involved in had strict, and usually very short, time-lines during which endorsers had to be collected. Most often, there was some important climate-related event underway that dictated when the open letters or other documents had to be published. How many scientists would have signed many of the above UE documents were there no time constraints is unknown.

A good example is ICSC’s November 29, 2012 open letter to UN Secretary General, Ban Ki-moon. As I explained in my December 4, 2012 FCPP OpEd, “Behind the scenes – preparing the open letter to the U.N. Secretary General on his climate science mistakes”:

  • “Some scientists said they agreed with the letter but did not want to sign because of job security concerns.
  • “Several of the people we most often hear about in media coverage of skeptics never sign these sorts of open letters no matter what the letter’s contents.
  • “Other did not sign up simply because they did not see the invitation in time (endorsements were collected in less than three days).
  • “Some said that, since their views are so well known, they wanted other climate realists to take the lead for a change.
  • “Some did not want to endorse anything that covered topics outside of pure science.”

The same problems collecting endorsers would have been experienced by the organizers of all the open letters listed above for the UE camp (i.e., not including ISPM07, TGGWS and the NIPCC which were not attempting to get large numbers of participants). To think that, these documents “capture the great majority of those contrarians presenting themselves as qualified experts or specialists in climate science or related disciplines” is irrational.

While some of these problems would also affect the endorser collection process for the CE camp, being on the political correct side makes it much more easier for CE scientists to endorse public statements of this nature (for more on this, see the end of my December 4 article).

Anderegg et al write concerning their work:

  • “Such expert analysis can illuminate public and policy discussions about ACC [anthropogenic climate change] and the extent of consensus in the expert scientific community.”
  • “…we have likely compiled the strongest and most credentialed researchers in CE and UE groups.”
  • “We provide a large-scale quantitative assessment of the relative level of agreement, expertise, and prominence in the climate researcher community.”
  • “…we provide a useful, conservative, and reasonable approach….”
  • “Based on the arguments presented here, we believe our findings capture the differential climate science credentials of the two groups.”

Obviously, none of these statements are even remotely credible. Yet, Anderegg et al is cited by Professor Peter Doran (co-author of the Doran and Zimmerman paper), as evidence to help substantiate their equally flawed work.

Dr. Spencer Weart, past Director of the Center for History of Physics of the American Institute of Physics and author of The History of Global Warming, summed up the feeling of many in the scientific community when he said that there were so many defects in Anderegg et al that the paper should never have been published.

Expert credibility in climate change”, the 2010 paper in the Proceedings of the National Academy of Sciences does make one contribution to the climate debate, however. It demonstrates that even peer reviewed papers in prestigious journals can be complete bollocks.


Tom Harris is Executive Director of the International Climate Science Coalition – and an advisor to the Frontier Centre for Public Policy in Winnipeg, Manitoba, Canada.