Tuesday, November 01, 2011

Judith Curry, Detection and Attribution and the IAC report

I was going to snark about the BEST (by which I mean funniest, there is clearly not much real science to speak of) climate science kerfuffle in a long time, but everyone else has beaten me to it, and I've nothing particularly witty to say about it (what do you mean, "no change there then"?) Have a look at Stoat for some links.

But while having a scan of the relevant blogs, I came across something else that struck me as worth mentioning.

It concerns La Curry's criticism of the IPCC, particularly the statement of WG1 that "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic GHG concentrations". Curry (and Webster) apparently don't like this statement. If they left it at that, then fmdidgad might be the most natural response, but rather than leaving it at that, they double down on it by asserting here that the IAC supports their view.

The relevant section of the IAC report is here, and it can be readily checked that their criticism which C&W quote was in fact aimed at the far more vague statements frequently made in WG2, and was clearly not intended to be applied to the WG1 statement at all. In fact, the WG1 statement is not imprecise in this sense at all, it is simply a one-sided probability statement of the general form "The probability of x > y is p". In this case x is the warming caused by anthropogenic effects, y is ~0.3C (being half the observed trend of ~0.6C) and p is 90%. Another IPCC statement of logically equivalent form is that the equilibrium climate sensitivity is very likely to be greater than 1.5C. If the IAC had intended their criticism to apply to the huge number of similarly-structured probabilistic statements in WG1, it is surely inconceivable that they would not have mentioned this criticism anywhere in the section where they actually address the treatment of probability in WG1. Indeed, the only place in that chapter where the IAC mention this issue of "imprecise statements, made without reference to the time period under consideration or to a climate scenario under which the conclusions would be true" is in that one section and even page where they are quite explicitly and specifically addressing WG2. There is, of course, nothing significantly ambiguous about the time period under consideration or the scenario under consideration in the statement that C&W object to.

I invite either of Curry and Webster to explain why they believe that the IAC intended this criticism, so clearly aimed at WG2, to apply to that D&A-based statement in WG1. Or alternatively, they could abandon their patently untenable claim that the IAC "shares their concerns" over this statement. Of course, I've been looking forward to Curry explaining her "Italian flag" blether for a long time now, to no effect. So I'm not holding my breath.


Steve Bloom said...

I point to Curry's Italian flag, and I point to Italy's pending bankruptcy.

wv says it's only logical (and I promise I'm not making this up): "spock"

Lazar said...

The logic eludes me, how detection of anthropogenic climate change is precluded by the variance of those spectral density estimates...

"X et al. object to our statement in the original manuscript: “Figure 9.4 of the IPCC AR4 shows that all models underestimate the amplitude of variability of periods of 40-70 years” on the basis that we do not consider the uncertainties presented in the chapter. Figure 9.4 is presented on a log-log scale, and the magnitudes of the uncertainties for both the model simulations and the observations are approximately a decade (factor of 10). Accounting for uncertainty, a more accurate statement would have been: The large uncertainties in both the observations and model simulations of the spectral amplitude of natural variability precludes a confident detection of anthropogenically forced climate change against the background of natural internal climate variability."

... the non-admission of undisputable error... a belief that the spectral density is of natural variability alone... and the post kicks off with annoying irrelevant comments about the reply somehow 'spouting' an 'IPCC party line' whatever that means... yuck.

James Annan said...

In my copy of the IPCC report, fig 9.4 is something entirely different, but assuming she means 9.7, she is clutching at straws if she thinks there is a substantial discrepancy there!

Martin Vermeer said...

James, seems your copy somehow landed on the Internet