JA is bored with climate sensitivity – because he knows the answer, 3 oC, and he may well be right. But other people don’t seem to have realised. And (via James again, I think) I ran across Tung and Camp on climate sensitivity, and Knutti et al.. They too think its 3 oC (well 2.8 +/- 0.9; and about 3). K et al. are doing this via CP.Net in J Climate; T&C via ERBE data in, they hope, Nature.
K et al. use the plausible idea that there could well be a relationship between the size of the seasonal cycle and the climate sensitivity of the model. And so they use 2500 perturbed-physics ensembles from the CP.Net experiment to derive a relation between seasonal cycle and sensitivity, and then say that predicts such-and-such given that we know the real cycle. Its interesting; not being my speciality I don’t really judge it, but I notice that: models with the wrong seasonal cycle are… wrong. Its not clear that you can usefully judge stuff from them. Another point on the same lines is that one criticism of the original CP.Net stuff was that they used a very thin set of model-reliability criteria, and it was suspected that including seasonal cycle might well filter out some of the very high (implauibly high) sensitivities. That now looks like being true. Secondly, this is all in HadSM3 perturbed. Secondly, if you look at their fig 2 then it seems that the relation is rather different amongst the different AR4 runs.
T&C use ERBE data, and some kind of fit to discriminate which bits of the sfc T is due to solar. I haven’t read it all yet; presumably this also gives you how much of the sfc T is solar, if you believe it, which would be interesting in itself. JA appears to promise his opinion in due course, so I may wait for that. Or I may perhaps find time and brain to read it myself.
Exercise (for the reader? for JA?): redo JA’s latest estimates, including the independant C&T values.
[A reader complains about excessive abbreviations. Sorry. I have excuses… anyway: CP.Net is climate prediction .net. ERBE is earths radiation budget experiment – a satellite (series). JA is James Annan. HadSM3 is the Hadley Centre climate model, version 3, slab version. sfc T is surface temperature. Wikipedia should expand those if you need more -W]