Energy & Environment

John Cook’s Leap of Faith

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Those who don’t accept absolutist and unsubstantiated claims about a scientific consensus on climate change are not in ‘denial.’

Crying “consensus” to defend absolutist assertions, climate activists are charging well beyond the threshold of what mainstream science can support. When they turn back toward the ledge to shout “denial” at anyone who has not leapt with them, the word no longer means what they think it does.

This was my argument in “Who’s The Denier Now?,” published in National Review last month. John Cook, lead author of the “97 percent consensus” studies, has responded to that piece by overstating a consensus in defense of an absolutist assertion and then accusing me of “denial.” He also objects to my citation of his work, which I will address first.

I cited Cook only to refute the claim by Senator Bernie Sanders that “97 percent of the scientists who wrote articles in peer-reviewed journals believe that human activity is the fundamental reason we are seeing climate change.” Specifically, I quoted from three studies that Cook surveyed in Environmental Research Letters, showing consensus levels of 78 percent (climate scientists), 82 percent (earth scientists), and 85 percent (scientists) for Sanders-like statements that attribute to humans a primary role in recent warming.

Cook does not question my accuracy, but instead argues that the consensus among climate scientists should be the relevant measure. Thus, for the 82 percent study, he notes that among the subsample of climate scientists the figure rises to 97 percent. For the 85 percent study, among the subsample of climate scientists the figure rises to 90 percent.

None of this changes the picture. Senator Sanders didn’t say climate scientists, he said peer-reviewed scientists. Even using Cook’s preferred subsamples, the range from 78 to 90 to 97 percent does not support an assertion of a 97 percent consensus.

Cook also misses the larger point, which is that Sanders (among others) has a habit of overstating scientific consensus. Besides the example above, I quote Sanders claiming that 97 percent of scientists conclude that climate change “is already causing devastating problems” and claiming that “the vast majority of scientists” say “there is a real question as to the quality of the planet that we are going to be leaving our children and our grandchildren.” I also quote former President Obama tweeting that 97 percent of scientists agree that climate change is “dangerous.” The documented consensus extends to none of these claims.

If Cook anywhere criticized those obvious mischaracterizations of his work as strongly as he now takes issue with my precise citation, I apologize for having missed it. [Update: In a March podcast (15:00-20:00), Cook and his colleague Peter Jacobs do note that Obama and Sanders overstate the consensus.]

He did comment approvingly on the inaccurate Obama tweet, which he said “raises the awareness of consensus” and “really helps in getting that information out into the general public.”

As for Cook’s own larger point, he seems focused less on an 85 versus 90 percent consensus than on the underlying conclusion about human responsibility for recent warming. But here things take a bizarre turn.

I fully accept mainstream science in my article. I quote the conclusion of the U.N. Intergovernmental Panel on Climate Change that it is “extremely likely that human activities caused more than half of the observed increase in [temperature] from 1951 to 2010.” I even criticize EPA Administrator Scott Pruitt for taking a contrary position:

[The Trump] administration should make clear that it works from mainstream scientific conclusions. EPA Administrator Pruitt confused matters greatly with comments to CNBC last month that went beyond his testimony about “precision” and “debate” and suggested that human activity was not the primary cause of recent warming. Pruitt had no basis for taking that position, nor does he gain anything from it; even Fox News confronted him.

Cook, on the other hand, rejects the IPCC statement as inadequate, insisting instead that “there is a consensus of evidence that human activity is causing all of recent global warming. Not some of it. Not even most of it. All of it.” None of the consensus studies in his survey even tested a statement as strong as that. Still, he concludes: “When the evidence converges on a single coherent conclusion, affirmed by a scientific consensus, we can accept the science or we can deny it.” Refusal to acknowledge this unsubstantiated “consensus” for “all of it” apparently constitutes “science denial.”

In support, he offers a chart that shows ten studies attributing at least 100 percent of recent warming to humans. But Cook has truncated the chart. In the original version on his website, there is a second set of bars for the share of warming that each study attributes to natural causes. Three of the studies show positive natural attributions, suggesting human attribution of less than 100 percent. Further, as his website notes, the bars show only best estimates and omit uncertainty ranges. So neither surveys of scientists nor their research justify the strength of Cook’s claim.

Neither surveys of scientists nor their research justify the strength of Cook’s claim.

For comparison, consider this characterization by NASA’s Gavin Schmidt: “The bottom line is that multiple studies indicate with very strong confidence that human activity is the dominant component in the warming of the last 50 to 60 years, and that our best estimates are that pretty much all of the rise is anthropogenic.” Compare, also, Cook’s bar chart to the probability distribution that Schmidt uses, which acknowledges uncertainty by showing a “best guess,” with humans entirely responsible, but also a significant chance that attribution is somewhere between 50 and 100 percent. Isn’t Schmidt’s communication both more accurate and more persuasive? Or is he in “science denial”?

All Cook accomplishes is to undermine the credibility of his other consensus-based assertions and to justify the emphasis that skeptics place on highlighting “uncertainty” and “debate.” Why emphasize, as Pruitt did in his confirmation hearing, that the “ability to measure with precision the extent of [human] impact is subject to continuing debate and dialogue”? Because of articles like Cook’s. Is agreement with the IPCC now a symptom of “denial”? Then many will suffer the condition gladly.

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