Saturday, September 08, 2007

Pile on!

It seems like everyone is having a go at Steven Schwartz these days: based on the links to my earlier post - and the "lurkers who support me via email" :-) - my commentary on his recent climate sensitivity estimate met with general approval (more on that later), but this post is about his own commentary on the IPCC report that I noticed previously in Nature (available here).

I didn't want to distract myself before by fisking it in detail, but it seems largely misguided. His opening sentence "The latest report from the Intergovernmental Panel on Climate Change assesses the skill of climate models by their ability to reproduce warming over the twentieth century..." is obviously wrong and the article does not improve much from there. There is a whole chapter (number 8) explicitly dedicated to assessing model performance, there is another chapter (6) on paleoclimate, and large parts of chapters 9 and 10 are also concerned with how we gain confidence in projections/probabilistic predictions. While 20th century climate change detection and attribution does get (IMO) a slightly unhealthy prominence in the report as a whole, it is hardly the whole story - indeed it has long been known that merely matching the general temperature trend is a rather weak test of model performance at least for the longer term (one detail that is worth noting is that all plausible models indicate a roughly linear trend over say 1980-2030, which does contribute to our confidence in a continuation of the recent warming trend).

A response from several IPCC authors has just appeared here, together with a brief rebuttal from Schwartz. The IPCC authors point out a number of reasons why Schwartz is wrong, and in his final rebuttal all he does is repeat his original erroneous claim that "in assessing the skill of climate models by their ability to reproduce warming over the twentieth century, the latest report from the IPCC may give a false sense of their predictive capability". It's just not true.

Coming soon: more on Schwartz and that sensitivity estimate.

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