Comments On The PNAS Article “Expert Credibility In Climate Change” By Anderegg Et Al 2010

An article has appeared in the Proceedings of the National Academy of Sciences:

William R. L. Anderegg, James W. Prall, Jacob Harold, and Stephen H. Schneider:, 2010: Expert credibility in climate change. Proceedings of the National Academy of Sciences. June 21, 2010, doi: 10.1073/pnas.1003187107.

The abstract of the paper reads

Although preliminary estimates from published literature and expert surveys suggest striking agreement among climate scientists on the tenets of anthropogenic climate change (ACC), the American public expresses substantial doubt about both the anthropogenic cause and the level of scientific agreement underpinning ACC. A broad analysis of the climate scientist community itself, the distribution of credibility of dissenting researchers relative to agreeing researchers, and the level of agreement among top climate experts has not been conducted and would inform future ACC discussions. Here, we use an extensive dataset of 1,372 climate researchers and their publication and citation data to show that (i) 97–98% of the climate researchers most actively publishing in the field support the tenets of ACC outlined by the Intergovernmental Panel on Climate Change, and (ii) the relative climate expertise and scientific prominence of the researchers unconvinced of ACC are substantially below that of the convinced researchers.

This paper is yet another example of the attempt to marginalize and “bin” scientists who differ from the IPCC perspective (except for those such as Jim Hansen who are more alarmist in their viewpoint) as my son has posted on in A New Black List.

There is an insightful well-balanced news article on the Anderegg et al PNAS  paper by Eli Kintisch titled

Scientists ‘Convinced’ of Climate Consensus More Prominent Than Opponents, Says Paper

I recommend readers of my weblog read Eli’s article. His news article includes an interesting statement by one of the authors of the PNAS article. It reads

Prall agrees that the system may not be perfect, but he thinks it’s good enough. “It’s conceivable that some people have formed a fixed point of view,” he says. “But the editors of journals, if they have formed a resistance to outside points of view, they have done so after years of seeing all the good, bad, and in-between papers. They know the field better than anyone else.”

I have served as Editors of several professional journals (e.g. Chief Editor of the Monthly Weather Review; Co-Chief Editor of the Journal of Atmospheric Science) and can categorically state that any Editors who have “formed a resistance to outside points of view” should not serve in the capacity of an Editor. This is a clear example of the type of prejudice that needs to be avoided in order to preserve the integrity of the scientific process.

John Christy is correct in his statement in the news article that there is “black listing” and my son’s post effectively summarizes this issue.

The blacklisting occurs in the review process of papers as John and Pat Michaels describe, in proposals for funding (e.g. see) and in the IPCC and CCSP assessment process (e.g. see).  This “black listing has even occurred in surveys as we found out when Fergus Brown, James Annan and I sought to publish a survey of climate scientists in the American Geophysical Union publication EOS; see

An Obvious Double Standard Adopted By The AGU Publication EOS

Weblogs By My Coauthors Of Our Rejected EOS Forum Article

My e-mail to Eli with respect to the PNAS article reads

 My son is 100% correct that I am not a “climate skeptic”.   Indeed, the IPCC is much too conservative at examining other human climate forcings that appear to have at least as large, or even larger effect, on the weather and other climate features that affect society and the environment.

Several of my colleagues (all AGU Fellows) recently published an article in EOS on our view.

The article is

Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R.
Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W.
Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,
J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate
change: The need to consider human forcings besides greenhouse gases.
Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American
Geophysical Union.

In this article we summarize evidence of three hypotheses

Hypothesis 1: Human influence on climate variability and change is of minimal importance, and natural causes dominate climate variations and changes on all time scales. In coming decades, the human influence will continue to be minimal.

Hypothesis 2a: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and involve a diverse range of first order climate forcings, including, but not limited to, the human input of carbon dioxide (CO2). Most, if not all, of these human influences on regional and global climate will continue to be of concern  during the coming decades.

Hypothesis 2b: Although the natural causes of climate variations and changes are undoubtedly important, the human influences are significant and are dominated by the emissions into the atmosphere of greenhouse gases, the most important of which is CO2. The adverse impact of these gases on regional and global climate constitutes the primary climate issue for the coming decades.

Only one of these hypotheses can be true.

Much of the climate science debate so far has been between hypothesis 1 (the “skeptic view”) and hypothesis 2b (the “IPCC view”). We present evidence in our paper, however, that these two hypotheses should be rejected (and there is much more on our broader view; e.g. see the 2005 NRC report –

We wrote in our EOS article, for example,

“In addition to greenhouse gas emissions, other first order human climate forcings are important to understanding the future behavior of Earth’s climate. These forcings are spatially heterogeneous and include the effect of aerosols on clouds and associated precipitation [e.g., Rosenfeld et al., 2008], the influence of aerosol deposition (e.g., black carbon (soot) [Flanner et al. 2007] and reactive nitrogen [Galloway et al., 2004]), and the role of changes in land use/land cover [e.g., Takata et al., 2009]. Among their effects is their role in altering atmospheric and ocean circulation features away from what they would be in the natural climate system [NRC, 2005]. As with CO2, the lengths of time that they affect the climate are estimated to be on multidecadal time scales and longer.”


“We recommend that the next assessment phase of the IPCC (and other such assessments) broaden its perspective to include all of the human climate forcings. It should also adopt a complementary and precautionary resource based assessment of the vulnerability of critical resources (those affecting water, food, energy, and human and ecosystem health) to environmental variability and change of all types. This should include, but not be limited to, the effects due to all of the natural and human caused climate variations and changes.”

Among our conclusions in the EOS article are

“The evidence predominantly suggests that humans are significantly altering the global environment, and thus climate, in a variety of diverse ways beyond the effects of human emissions of greenhouse gases, including CO2. Unfortunately, the 2007 Intergovernmental Panel on Climate Change (IPCC) assessment did not sufficiently acknowledge the importance of these other human climate forcings in altering regional and global climate and their effects on predictability at the regional scale. It also placed too much emphasis on average global forcing from a limited set of human climate forcings. Further, it devised a mitigation strategy based on global model predictions…..Because global climate models do not accurately simulate (or even include) several of these other first order human climate forcings, policy makers must be made aware of the inability of the current generation of models to accurately forecast regional climate risks to resources on multidecadal time scales.”

There has been little discussion, unfortunately, on our broader perspective of the role of humans in the climate system, which I hope you can help change.

Best Regards

Roger Sr.

The Anderegg et al  paper is another in a set of advocacy articles in the Proceedings of the National Academy of Sciences (see and see). This paper illustrates more generally how far we have gone from the appropriate scientific process.

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