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mercredi 13 avril 2016

Encore le consensus qui refait surface

Tel un serpent de mer voici que Richard Tol réapparait à la surface en publiant quelque chose sur le "consensus", un sujet qui semble lui tenir particulièrement à cœur.

A noter que Richard Tol ne nie pas que ce consensus existe et se situe très près des 100%:
  • Richard Tol says:
    The consensus is of course in the high nineties. No one ever said it was not. We don’t need Cook’s survey to tell us that.
    Cook’s paper tries to put a precise number on something everyone knows. They failed. Their number is not very precise.
Bizarre, bizarre... Donc apparemment Richard Tol fait tout un foin parce que l'étude initiale de Cook (appelée Cook13) serait entachée d'erreurs, ce que Sou à Hotwhooper a maintes fois démonté, par exemple dans son dernier billet:
  • By far the biggest flaw in Richard's thinking is when he assumes that "no position" is the same as "it's not human activity".  When Cook13 came up with 97% consensus, it was 97% of abstracts that expressed a position on the cause of modern warming. It wasn't 97% of all papers in their larger sample. It wasn't a percentage of all scientific papers ever published on climate. It wasn't a percentage of all scientific papers in the world on any topic. No. It was a percentage of all the papers in the sample that expressed a position on the cause of warming.
  • Nowhere in Richard's paper did I see him use his wrong arithmetic on the proportion of papers that disputed the fact that humans have caused global warming. If he had, he'd have written about how only 0.7% of the larger sample disputed this fact.  You can see where I got that number from in the table above. Of all the 11,944 papers in the full sample, there were only 78 that disputed the fact that humans are causing global warming and 78/11,944 = 0.7%. Of course the proper calculation is the proportion in the sub-sample that took a position, which is 4,014. When you do the proper arithmetic: 78/4,014, you get 1.9% - still a very small number and one that Richard Tol doesn't mention in his comment.

Ce qui est marrant (et que j'ai du mal à m'expliquer) est que le même jour où Tol publie son "étude", une autre parait dans la même revue, co-signée par Cook, Oreskes, Lewandowsky, entre autres.

Comparons les deux résumés.

Celui de Tol:
  • Cook et al's highly influential consensus study (2013 Environ. Res. Lett. 8 024024) finds different results than previous studies in the consensus literature. It omits tests for systematic differences between raters. Many abstracts are unaccounted for. The paper does not discuss the procedures used to ensure independence between the raters, to ensure that raters did not use additional information, and to ensure that later ratings were not influenced by earlier results. Clarifying these issues would further strengthen the paper, and establish it as our best estimate of the consensus.
Celui de Cook16:
  • The consensus that humans are causing recent global warming is shared by 90%–100% of publishing climate scientists according to six independent studies by co-authors of this paper. Those results are consistent with the 97% consensus reported by Cook et al (Environ. Res. Lett. 8 024024) based on 11 944 abstracts of research papers, of which 4014 took a position on the cause of recent global warming. A survey of authors of those papers (N = 2412 papers) also supported a 97% consensus. Tol (2016 Environ. Res. Lett. 11 048001) comes to a different conclusion using results from surveys of non-experts such as economic geologists and a self-selected group of those who reject the consensus. We demonstrate that this outcome is not unexpected because the level of consensus correlates with expertise in climate science. At one point, Tol also reduces the apparent consensus by assuming that abstracts that do not explicitly state the cause of global warming ('no position') represent non-endorsement, an approach that if applied elsewhere would reject consensus on well-established theories such as plate tectonics. We examine the available studies and conclude that the finding of 97% consensus in published climate research is robust and consistent with other surveys of climate scientists and peer-reviewed studies.
J'ai le sentiment que chacun "accuse" l'autre de cherry-picking, quoi qu'il en soit le consensus n'est pas en lui-même vraiment remis en cause par Richard Tol, non seulement il le reconnaît himself dans un commentaire comme on l'a vu plus haut, mais dans son récent opus il se contente finalement de dire que "Clarifying these issues would further strengthen the paper, and establish it as our best estimate of the consensus."

Bref il ne fait rien d'autre que jeter le doute sur les études de Cook et al sans vraiment apporter de l'eau à son moulin.

Au fait, comme le rappelle Sou:
  • Richard Tol is not an "independent" researcher. He is one of the advisers to the anti-mitigation lobby group the Global Warming Policy Foundation in the UK, which is an activist lobby group for more, not less, global warming. Whether Richard is trying to prove his worth to the GWPF, or whether he is only driven by an obsession with trying to find a flaw in Cook13, we'll probably never know. He is obsessed to the extreme, there's plenty of evidence for that even here at HotWhopper - see here and here.

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