Georgia Tech climatologist Judith Curry dealt a serious blow to the appeal to consensus on climate change in her paper “Climate Change: No Consensus on Consensus,” three years ago. She pointed out (among lots of other valuable things) that, whatever value consensus might have in science (as opposed to politics), consensus is significant only if it arises spontaneously, but the alleged consensus on climate change had been assiduously manufactured by the IPCC.

She’s followed the subject a good deal more in the intervening time, and yesterday she posted a new piece that administers a well-deserved spanking to John Cook, Dana Nucitelli, et al., for their latest bit of nonsense on consensus (linking some of the better critiques of Cook et al.’s earlier bit of nonsense), and then goes on to point out that when properly defined and measured, consensus on climate change turns out to be much less than the 97% Cook et al. (and President Obama parroting them) claim. She gives good reasons to think the real consensus might instead be around 47%—and then shows that even that would be an exaggeration by pointing out that only a small fraction of the scholars surveyed to arrive at that conclusion are actual scholars on the crucial point in question: detection and attribution. Here’s that section:

Who’s opinion ‘counts’?

Surveys of actual climate scientists is [sic] a much better way to elicit the actual opinions of scientist on this issue. But surveys raise the issue as to exactly who are the experts on the issue of attribution of climate change?  The Verheggan et al. study was criticized in a published comment by Duarte, in terms of the basis for selecting participants to respond to the survey:

“There is a deeper problem. Inclusion of mitigation and impacts papers – even from physical sciences or engineering – creates a structural bias that will inflate estimates of consensus, because these categories have no symmetric disconfirming counterparts. These researchers have simply imported a consensus in global warming. They then proceed to their area of expertise. [These papers] do not carry any data or epistemic information about climate change or its causes, and the authors are unlikely to be experts on the subject, since it is not their field.

Increased public interest in any topic will reliably draw scholars from various fields. However, their endorsement (or rejection) of human-caused warming does not represent knowledge or independent assessments. Their votes are not quanta of consnsensus, but simply artifacts of career choices, and the changing political climate. Their inclusion will artificially inflate sample sizes, and will likely bias the results.”

Roy Spencer also addresses this issue in his Senate testimony (cited above):

“(R)elatively few researchers in the world – probably not much more than a dozen – have researched how sensitive today’s climate system is based upon actual measurements. This is why popular surveys of climate scientists and their beliefs regarding global warming have little meaning: very few of them have actually worked on the details involved in determining exactly how much warming might result from anthropogenic greenhouse gas emissions.”

The number of real experts on the detection and attribution of climate change is small, only a fraction of the respondents to these surveys.  I raised this same issue in the pre-Climate Etc. days in response to the Anderegg et al. paper, in a comment at Collide-a-Scape (referenced by Columbia Journalism Review):

The scientific litmus test for the paper is the AR4 statement: “anthropogenic greenhouse gases have been responsible for “most” of the “unequivocal” warming of the Earth’s average global temperature over the second half of the 20th century”.

The climate experts with credibility in evaluating this statement are those scientists that are active in the area of detection and attribution. “Climate” scientists whose research areas is ecosystems, carbon cycle, economics, etc speak with no more authority on this subject than say Freeman Dyson.

I define the 20th century detection and attribution field to include those that create datasets, climate dynamicists that interpret the variability, radiative forcing, climate modeling, sensitivity analysis, feedback analysis. With this definition, 75% of the names on the list disappear. If you further eliminate people that create datasets but don’t interpret the datasets, you have less than 20% of the original list.

Apart from Anderegg’s classification of the likes of Freeman Dyson as not a ‘climate expert’ (since he didn’t have 20 peer reviewed publications that they classed as ‘climate papers’), they also did not include solar – climate experts such as Syun Akasofu (since apparently Akasofu’s solar papers do not count as ‘climate’).

But perhaps the most important point is that of the scientists who are skeptical of the IPCC consensus, a disproportionately large number of these skeptical scientists are experts on climate change detection/attribution.  Think Spencer, Christy, Lindzen, etc. etc.

Bottom line:  inflating the numbers of ‘climate scientists’ in such surveys attempts to hide that there is a serious scientific debate about the detection and attribution of recent warming, and that scientists who are skeptical of the IPCC consensus conclusion are disproportionately expert in the area of climate change detection and attribution. [Emphasis added.]

Little by little, bit by bit, CAGW’s house of cards is collapsing. Judith Curry, whose courage led her first actually to dare to interact seriously with CAGW skeptics (beginning with Steve McIntyre, Ross McKitrick, and others at ClimateAudit.org) and then, on seeing that their data were excellent and arguments strong, to adjust her own views, bit by bit, from warmist to lukewarmist to now one of the most prominent skeptics, deserves considerable credit and honor.

 

 

Featured image courtesy of ClimateDepot.com.