William R. L. Anderegg, James W. Prall & Jacob Harold, PNAS 107 (39), Reply to O’Neill and Boykoff: Objective classification of climate experts

Proceedings of the National Academy of Sciences, Vol. 107, No. 39, E152; published online before print August 31, 2010;  doi: 10.1073/pnas.1010824107

Reply to O’Neill and Boykoff: Objective classification of climate experts

1. William R. L. Anderegg^a,¹, 
2. James W. Prall^b, and 
3. Jacob Harold^c

1. 
   
   ^aDepartment of Biology, Stanford University, Stanford, CA 94305;
2. 
   
   ^bElectrical and Computer Engineering, University of Toronto, Toronto, ON, Canada M5S 3G4; and
3. 
   
   ^cWilliam and Flora Hewlett Foundation, Palo Alto, CA 94025

The landscape of expert perspectives on anthropogenic climate change (ACC) is a complex area, and thus, classifying individuals in terms of their perspectives is necessarily challenging (1). Although O’Neill and Boykoff (2) seek to illuminate this landscape, their semantic objection to our article does not adequately consider our methods or the background literature on denialism or climate change contrarians.

O’Neill and Boykoff (2) take issue with us including “climate denier” as one of the article’s key terms, citing its supposed moralistic tone and potential link with Holocaust denial. However, denialism has been well established in the literature as a relevant and appropriate concept and frequently applied to the ACC discourse (3–5). Furthermore, Dielthelm and McKee (3) recommend that denialism be responded to by public scrutiny and examination of denialist expertise as our article provides.

O’Neill and Boykoff (2) highlight differences between climate skepticism and contrarianism. However, their claim that our indiscriminate use of these terms and our classification of individuals into unconvinced (UE) or convinced by the evidence (CE) groups will polarize discourse does not carefully consider our methods and paper’s text. We use “skeptic/contrarian” in the article’s Introduction and conclusion in accordance with existing social science literature (e.g., refs. 4 and 6), as encouraged by our reviewers in multiple rounds of peer review. We state in the first paragraph that all three terms—skeptic, contrarian, and denier—have been used in the literature, and thus, we use these terms to place our study in context. We do not, however, use the terms indiscriminately regarding our study groups. In fact, we do not use these terms at any point in ourMaterials and Methods or Results, focusing only on the UE/CE groups.

O’Neill and Boykoff (2) fail to note that our methods cannot differentiate—and do not claim to—positions within the UE group. We agree that such differentiation would be ideal; however, the strength of our UE categorization is that it rests on the objective classification of individuals based on their publicly stated opinions, and not our subjective determination of individuals’ beliefs and/or motives as would be needed to create O’Neill and Boykoff’s distinctions. They imply that our entire UE group could be labeled as “contrarians.” We disagree. Such a priori blanket labeling could further polarize the discourse. Few would claim that statements early in the examined 1992–2009 time period were attacking a perceived “false consensus,” making the label contrarian inappropriate. Moreover, by their definition, we would need to demonstrate frequent financial support from industry or ideological motives to those in the UE group, which again would necessitate subjective judgment. By contrast, our UE group presents a categorization that is accurate, objective, inherently more neutral in tone, and makes no assumptions about individuals’ funding, ideology, or motives.

We acknowledge that our UE category may encompass climate change skeptics, deniers, and contrarians. Nonetheless, it provides an objective and useful categorization of those who challenge the consensus on ACC. O’Neill and Boykoff’s semantic objections (2) do not adequately consider our methods or alter any conclusions of the article.

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Acknowledgments

We would like to dedicate this paper and reply to Dr. Stephen H. Schneider, who passed away July 19, 2010. An inspiration for the scientific community, Dr. Schneider strove ceaselessly to communicate climate science and expertise during his 40-year career.

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• ¹Correspondence e-mail:  anderegg@stanford.edu.
• 
  
  Author contributions: W.R.L.A., J.W.P., and J.H. designed research; and W.R.L.A., J.W.P., and J.H. wrote the paper.
  
  Link:  http://www.pnas.org/content/107/39/E152.full
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