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‘But aren’t 97 per cent of climate scientists sure that humans are causing global warming?’

By Don Aitkin - posted Friday, 22 April 2016


One of the most frequently used rhetorical devices to avoid answering the questions of the critics of the AGC scare is the proposition that there is a astonishing scientific ‘consensus’ on the point: some 97 per cent of climate scientists are said to agree. By implication, the other 3 per cent are simply ignorant, mavericks or troublemakers, to be lumped in with other people who fall into the category ‘climate deniers’. We are thus asked to accept the authority of the consensus, and to cease and desist from questioning anything about global warming or ‘climate change’.

To deal with this part of the debate we need to go back to the beginning. The AGW scare is built around three core propositions: that the earth is warming, that the warming is caused by human activities, especially the burning of fossil fuels, and that the warming is dangerous. It is said, or implied, that 97 per cent of ‘climate scientists’ agree with this triad. In fact President Obama’s office tweeted exactly this statement in 2015: Ninety-seven percent of scientists agree: #climate change is real, man-made and dangerous.

Science is rarely a matter of consensus, and where it is so what we are usually talking about is the material that goes into textbooks, for beginning students need to have some understanding of what is generally agreed to be the case (some of what I learned in high school science is now generally agreed to be wrong or irrelevant). As students get to be more senior, they are exposed to argument, and taught to explore and test the hypotheses and evidence that lie behind what has been published. In experimental science, consensus is simply current opinion, and it can be quite wrong. As Einstein said, when a group of scientists in 1931 published a book Hundert Autoren gegen Einstein (‘One hundred authors against Einstein’), ‘Why one hundred? If I were wrong, then one would be enough!’ That one would have conducted the experiment whose results showed conclusively that Einstein’s hypothesis must be wrong, but none of the hundred had done that. They were simply expressing their separate opinions.

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Now, what do ‘climate scientists’ actually say? I’ve put inverted commas around the term because there is no agreed meaning for it. Most of the leading figures in this sub-field have degrees in other disciplines, whatever the title of their current chair. The ’97 per cent’ figure is supported by three different published articles, with a forerunner by Naomi Oreskes, about whom I wrote a little while ago. In 2004 she looked at 928 abstracts of articles in the climate science field. According to her, 75 per cent supported the view that human activities were responsible for most of the warming in the last fifty years. Now we should stop for a moment to observe that the scientists themselves had said nothing. She had not interviewed them. Instead, she had looked at the abstracts of their articles, and come to a view about what their authors must have thought. Why those 928? Well, they were the papers in the ISI database from 1993 to 2003 that had the words ‘climate change’ as a tag. Ms Oreskes seemed somehow to have excluded articles by scientists such as Christy, Lindzen, Michaels and Idso, all of them sceptics, and somewhat to their surprise. What was the method of evaluation? She divided the papers into six groups and found that 75 per cent of them either explicitly or implicitly accepted the ‘consensus view’. What was that? In her words: the evidence for human modification of climate is compelling. Is that a bad thing? That seems not to have been part of her survey, but one might infer that for her the outcome must be bad. You’ll have noticed that she looked only at abstracts, and did not read the full articles in question.

We move on. In 2009 Zimmerman and Doran asked scientists two questions: did they think that temperatures had risen and whether humans were significantly responsible. Again, no mention of dangerous consequences, but at least the authors did actually ask some scientists what they thought. But then the methodology gets very sloppy, and I’ll summarise it like this. They used an online survey of 10,257 members of the American Geophysical Union, whose membership is around 60,000. The respondents seemed to be the right ones to interview, given their fields of interest, but only 3,146 actually replied. Now they excluded nearly all of those who had replied, for one reason and another, to produce 79 scientists who said they were climate scientists and had published more than half of their work on ‘climate change’. Of them 77 both thought that temperatures had risen and that humans were significantly responsible. The fraction 77/79 gives you 97 per cent, and I think that’s the first occasion the figure came up. Consensus had been found! I say no more. Some methodology is just so bad you can’t credit that a responsible journal would publish it. Alas, even worse is to come.

A year later Anderegg et al explored the work of 200 of the most prolific writers on ‘climate change’ and argued that 97% to 98% of the 200 most prolific writers on climate change believe “anthropogenic greenhouse gases have been responsible for ‘most’ of the ‘unequivocal’ warming.” So they too got a 97 per cent figure. Again, no mention of any danger from warming. Again, no one was asked anything. The authors started with 1372 scientists whom they assessed to be the leading ones in the field, and winnowed them down to 200 of the really top. Then they just read, and made a decision from their reading. The 97 per cent were well published and agreed with the orthodox position; the 3 per cent were well published and did not agree.

The crème de la crème  comes with the work (if that is right term for it) of John Cook, occasionally aided by Stefan Lewandowsky. I’ve written about their ‘contribution’ to science more than once, as here, for example. In 2013 Cook et al and a team of volunteers looked at more than 12,000 abstracts, rated them according to whether or not they implicitly or explicitly endorsed the view that human activity had caused (wait for it) some of the warming, and again found the magic 97 per cent. See — it’s true! Surely those three separate ratings of 97 per cent have something going for them.

On the face of it, no. Unfortunately for Cook, Legates and others later in the same year published a rebuttal. They found that only 41 papers – 0.3% of all 11,944 abstracts or 1.0% of the 4,014 expressing an opinion, and not 97.1% – had been found to endorse the claim that human activity is causing most of the current warming. Elsewhere, Craig Idso, Nicola Scafetta, Nir J. Shaviv and Nils-Axel Morner and other climate scientists protested that Mr. Cook ignored or misrepresented their work. Cook has been trying to defend his results ever since, but more and more scorn has, in my view quite rightly, been poured on the work. You can read some of the objections here, here and here, for starters. As I have said before, this is terrible stuff methodologically, the worst I’ve ever seen in a peer-reviewed journal.

Let’s summarise. Point one: none of these papers asked whether or not AGW was dangerous to humanity or anything else. So none of them is evidence for the Obama tweet set out at the beginning of this essay. As a self-styled lukewarmer, I have no difficulty in nodding about propositions that the earth has warmed over the last 150 years, or that human activity has made some contribution to that warming. With the evidence available, it seems to me unlikely that the human contribution has been crucial, for two reasons. First, there was a decided hiatus over 18 years, when global temperature anomalies went up and down with little average change, while carbon dioxide accumulations kept on rising steadily. The end of the hiatus came not with a burst of CO2, but with a powerful el Nino, already subsiding quickly. Second, there are plainly other factors at work, and if they were at work in the past, why are they not generally at work?

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Point two: the belief that global warming is bad for everything and everyone comes from two notions. The first is that simple linear extrapolations from the period 1975 to 1998 made it it look as though warming would go on and on, and that was the fear at the end of the 20th century. As we know, that didn’t happen. Second, the GCMs on which the IPCC based its projections or scenarios for the 21st century tell us that it must happen, in part because they are built on the notion that carbon dioxide accumulations must rise and rise, and bring on large increases of temperature caused by the notion of strongly positive climate sensitivity. I dealt with that in the #7 essay.

If there is anything like a consensus, given what I have read over the past ten years, it would be around the lukewarm position: the planet is warmer than it was 150 years ago, though not in an unprecedented way, and that human activity in burning fossil fuels, clearing land and making cement has had something to do with that warming. More than that is simply contestable, and more contestable now than it was thirty years ago.

And that people keep referring to the magic 97 per cent figure, as though it means something, is to me a sign of a closed mind and a quasi-religious belief in the scare. Such people seem to me intellectually lost souls.

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This article was first published on Don Aitkin.



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About the Author

Don Aitkin has been an academic and vice-chancellor. His latest book, Moving On, was published in 2016.

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