James Annan has a must-read post on climate sensitivity today, picking up on the Norwegian study, Nic Lewis's work and the contents of the leaked IPCC report. Here are some choice excerpts:
As I said to Andy Revkin (and he published on his blog), the additional decade of temperature data from 2000 onwards (even the AR4 estimates typically ignored the post-2000 years) can only work to reduce estimates of sensitivity, and that's before we even consider the reduction in estimates of negative aerosol forcing, and additional forcing from black carbon (the latter being very new, is not included in any calculations AIUI). It's increasingly difficult to reconcile a high climate sensitivity (say over 4C) with the observational evidence for the planetary energy balance over the industrial era.
Since the IPCC can no longer defend their old analyses in any meaningful manner, it seems they have to resort to an unsupported "this is what we think, because we asked our pals". It's essentially the Lindzen strategy in reverse: having firmly wedded themselves to their politically convenient long tail of high values, their response to new evidence is little more than sticking their fingers in their ears and singing "la la la I can't hear you".
The paper I refer to as a "small private opinion poll" is of course the Zickfeld et al PNAS paper. The list of pollees in the Zickfeld paper are largely the self-same people responsible for the largely bogus analyses that I've criticised over recent years, and which even if they were valid then, are certainly outdated now. Interestingly, one of them stated quite openly in a meeting I attended a few years ago that he deliberately lied in these sort of elicitation exercises (i.e. exaggerating the probability of high sensitivity) in order to help motivate political action. Of course, there may be others who lie in the other direction, which is why it seems bizarre that the IPCC appeared to rely so heavily on this paper to justify their choice, rather than relying on published quantitative analyses of observational data.
This comment submitted by Annan to the Fifth Assessment report process is fun too:
It seems very odd to portray our work as an outlier here. Sokolov et al 2009, Urban and Keller 2010, Olson et al (in press JGR) have also recently presented similar results (and there may be more as yet unpublished, eg Aldrin at the INI meeting back in 2010). Such "observationally constrained pdfs" were all the rage a few years ago and featured heavily in the last IPCC report, there is no clear explanation for your sudden dismissal of them in favour of what seems to be a small private opinion poll.
And there are some interesting comments on Nic Lewis's work too. Great fun. Read the whole thing.