From http://www.columbia.edu/~jeh1/mailings/2011/20110415_EnergyImbalancePaper.pdf. The email that pointed me at it said “Sincere apologies — I am very sorry that I did not have time to write a shorter paper” and I think he is correct to apologise. It also says “Climate sensitivity section probably belongs in the paleo paper still under review” which also seems correct – to devote 15 pages (more than 1/4 of the paper!) to saying that Climate Sensitivity is ~ 3 oC is to confess that your prose is too prolix – and he doesn’t even quote JA (which brings up another topic: he spends far too much time quoting himself. The entire thing is far too inward looking).
I did some minor due diligence before writing this, to see who else had written about it. Predictably enough Curry wrote a post – but also predictably enough she didn’t actually bother read, let alone analyse, the paper; and the long tedious discussion thread there appears to be totally worthless.
Speaking of which, there is some irritating twee nonsense in Hansen’s paper about Sophie and Connor’s estimes or aerosol forcing. Apparently they are Hansens grandchildren. Why their opinion matters is a total mystery. But I don’t put my cat in scientific papers and Hansen should leave his grandchildren out, if he is writing science. If he is writing propaganda, then fine, he can be photographed kissing babies all he likes.
The next issue is the degree of heat mixing into the deep ocean. Hansen would like his model (GISS modelE-R) to over-estimate it;, for reasons that will become clear when we discuss section 7, below. Why does he believe this? First, the ocean model mixes too rapidly into the deep Southern Ocean, as judged by comparison to observed transient tracers such as chlorofluorocarbons (CFCs) (Romanou and Marshall, private communication, paper in preparation). Second, the ocean thermocline at lower latitudes is driven too deep by excessive downward transport of heat, as judged by comparison with observed ocean temperature (Levitus and Boyer, 1994). Third, the model’s second-order finite differencing scheme and parameterizations for turbulent mixing are excessively diffusive, as judged by comparison with relevant observations and LES (large eddy simulation) models (Canuto et al., 2010). Notice what *isn’t* there – comparison with other models. Like I said, this is too navel-gazing. Does Hansen never talk to other modelling groups? (well, I’m being a bit unfair; perhaps his paper is just badly edited, because later on there is some (slightly non-systematic) comparison against some other modelling groups. But that is rather post-hoc). Of his 3 reasons: the first is unpublished. The second appears to be an ad-hoc comment he has just made here, rather than what you’d expect (a paper discussing that issue). The third is possible; I haven’t read Canuto so can’t judge. But 1 out of 3 isn’t great, and his solution: for the time being, we estimate alternative climate response functions based on intuition tempered by evidence of the degree to which the model tracer transports differ from observations in the Southern Ocean and the deepening of the thermocline at lower latitudes isn’t going to play well with anyone who doesn’t already believe him. I can’t see how this could get published.
Weirdly, page 22 claims that the Hadley Centre model (which one?) has a sensitivity of 10 oC to 2*CO2, which doesn’t sound at all plausible. Implicitly, he is talking about HadCM3, in which case he is simply wrong.
Then (section 7) Hansen goes on to say, if the models mix heat down too fast, yet roughly reproduce the observed T over the last century, this must be because they have overestimated the forcing; which he proposes is because they have underestimated the aerosol cooling. In which case – ta da – we’ll be in trouble later on, because the warming will be faster than we expect. And who knows? He could be correct. Certainly there is room for much uncertainty in the aerosol forcing.
Um, well, there you go. There was some other stuff too, but it was less exciting.