Saturday, October 29, 2005

New paper

Those who keep a close eye on my work page (yeah, right) will have noticed a new preprint appeared there recently: Efficiently constraining climate sensitivity with paleoclimate simulations. SOLA Vol 1 pages 181-184 2005. It's only a short 4-page summary in a rapid response journal (just right for sneaking inside the IPCC deadlines) but breaks new ground in 3 ways which I hope will help to point the way forward for climate prediction.
  • We use an efficient multivariate parameter estimation method with a state-of-the-art GCM for the first time. This is many many orders of magnitude more efficient than multifactorial sampling, and several people have told us over the last couple of years that it couldn't be done. (I won't deny it has some potential drawbacks, though - but we haven't found any show-stoppers).
  • We have tried to take some account of model inadequacy - by which I mean the fact that there are no "correct" parameters for which the model actually looks just like the real world, so the standard "perfect model assumption" is wrong.
  • We have used out-of-sample data (in this example, a simulation of the Last Glacial Maximum) to attempt to improve the rigour with which predictive skill is assessed. Merely managing to fit a set of data doesn't automatically mean that the model will skillfully predict climate under a different forcing!
All of these 3 aspects are approached in a rather simplistic manner, and all can (and no doubt will) be improved, eventually by us if no-one else does it first. But it's good to have a benchmark, if only a rather low one, to shoot for in subsequent work.

Oh, by the way, we didn't really learn anything startling about climate sensitivity. But we all know that's about 3C anyway :-)

4 comments:

crandles said...

Interesting.

Dave Stainforth has asked me to hassle him again in December to write something for the the CP board on sampling strategy.

When I do so, should I ask him to comment on this paper?

When we discussed it in the past, I did to a certain extent challenge whether it was justified to say: "comprehensive multiple-perturbed parameter ensembles appear to be necessary for robust probabilistic analyses".

That was before I read up about your ensenble Kalman filters work. Had I known about this then, I might have been a little more robust.

James Annan said...

Chris,

Well, I started to write a rant about cpdn but deleted it...because by December I predict that this recent paper will be well down the list of topics of interest. We have some much more exciting news which I cannot mention quite yet...watch this space!

Lumo said...

Hi James, can you solve this conundrum? ;-)

James Annan said...

Lubos,

Yes of course I can. It is genuinely sad to see talent go to waste in such a manner. I suspect that he does not want to make a positive contribution to actually expanding our knowledge precisely because he knows where an honest open-minded investigatin will inevitably lead. I won't suggest that Kolmogorov's comment applies also in this case, as clearly the subject of your post is a entirely different calibre of human to you.

Changing the subject entirely :-) I may be tempted to post my own opinions on the hockey stick issue, although I'm not entirely convinced that it is worth wasting that many electrons on...I do look forward to the response to Roger Pielke's challenge.