It is time to stop quivering in our boots in pointless fear of the future and just roll up our sleeves and build it.
- Ray Pierrehumbert

Friday, April 13, 2007

Annan vs Hegerl goes Nuclear in a Hurry

Strange day.

I just returned from a day that included a talk by Gabrielle Hegerl to discover that James Annan has a poster criticizing an aspect of her work.

In fact, the point that James makes, was, in essence, covered in her talk. She said the data alone was insufficient to remove the long tail, but she was clear that the long tail was almost certainly an artifact of
the way the problem was set up. I believe that James' approach amounts to begging the question: if you assert a prior where there are no tails, you can't say the data has constrained the tail. This seems to me like hair-splitting, though I expect James will disagree.

OK, fine, here I am at Bayesian central, I suppose seeing some technical battles between my virtual friends and my real-world acquaintances is to be expected in the rough and tumble world of science, but it's a bit of an odd coincidence.

So to see if there is some ongoing longer feud between these two, I googled "Annan Hegerl", and who should pop up but Lubos Motl! My God, this article was uploaded tomorrow (dateline artifacts). It appears negativeland is already all abuzz with the fact that a climate scientist would dare to criticize another!

(We are damned if we criticize each other and dmaned if we don't, but still, this is ridiculous.)

And see this on the SEPP site (with similar comments from Motl):

Three weeks ago, Hegerl et al. published a text in Nature that claims that the 95 percent confidence interval for the climate sensitivity is between 1.5 and 6.2 Celsius degrees. James Annan decided to publish a reply (with J.C. Hargreaves). As you might know, James Annan - who likes to gamble and to make bets about global warming - is

an alarmist who believes all kinds of crazy things about the dangerous global warming;

a weird advocate of the Bayesian probabilistic reasoning".

However, he decided to publish a reply that

the actual sensitivity is about 5 times smaller than the Hegerl et al. upper bound which means that the warming from the carbon dioxide won't be too interesting;

Now, leaving aside how weird it is for anyone, let alone the ever-rigorous James, to be called "a weird advocate of the Bayesian probabilistic reasoning" (!!!!) doesn't this read like weird Bayesian James has become almost Lindzenite, putting an upper bound on the sensitivity at 6.2/5 or about 1.25 C?

No. Weird Bayesian James advocates using 20/5 or 4 C as an upper bound. Elsewhere he comes up with 3 C as a best estimate. Which is higher than Gabi's!!!

I assure you Hegerl knows the long tail is an artifact; that the higher the cutoff the longer the tail; that it tells us nothing.

The only question is how to handle it. It can easily be misinterpreted either way you approach it. James' approach can be seen as begging the question. Can you really put your hypothesis in as your prior?

And how (to get back to my blog theme) do we go about explaining any of this to the general public now that the engines of apoplectic confusion are gearing up to make a case out of this?

Note to the lay reader; James will correct me if I am wrong, but I am pretty sure he does not claim that the sensitivity is certain to be less than 1.3 C.

Anyone care to make a bet?

[Update: apparently all this denialist noise was from last year. Still...]

1 comment:

Steve Bloom said...

I sure was getting a feeling of deja vu reading this post. I'm glad to hear it's all behind us.

IMHO this shows that science disagreements are hard for the noise machine to do much of anything with if average people cannot understand the subject matter.