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Old 06-02-2013, 05:19 PM
Michael Reach Michael Reach is offline
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Join Date: Apr 2013
Location: Baltimore, Maryland, USA
Posts: 71
Default Re: Data snooping and science

Elroch, I was pretty resolved to stay out of discussing the actual science, since, as I said, I don't know much about it. But I am having trouble following what you're saying.
First, I'm not sure what you mean by the "complete certainty" of the physics. Probably you mean that one aspect of the physics, the amount of heating that CO2 would cause other things being equal, is simple physics. But I don't know why you think that should help Dr. Muller's statement, since other things are not equal. The tough part of the job is going to be to figure out what role all the other factors play. In the end, as you mentioned, the size of the feedbacks is a critical issue, with estimated values ranging (near as I can tell) over a factor of six or so, or maybe a factor of two from more recent work. And without the feedbacks, the basic sensitivity to CO2 would be much less concerning.
In any case, I don't think that was what Muller was saying. Obviously, if all he needs is to estimate a single parameter, that he can estimate it with one parameter isn't going to impress most skeptics very much! My impression from the video (and from some comments by his co-worker Steve Mosher elsewhere) is that they found that the best fit to the data was given by fitting the CO2 and dropping all other variables. Even volcanoes, which have an obvious immediate impact, dropped out if you look over a few years span, and he was left with no explanatory variables that helped except CO2.
Anyhow, if that's what he was saying, that's what I was asking: to what extent is he allowed to do that, and to what extent do we say that he's using a lot of hypothesis choices made by others?

"One thing that annoys me is when denialists argue against global warming on the basis of short term data." That's interesting: From a Bayesian point of view, the last decade of data shouldn't "argue against global warming", but it certainly must bring down the estimate of the climate sensitivity to CO2: that's pretty much automatic from Question 20 on the final! How much is going to be an important question. I believe there's a lot of discussion right now about a couple of papers currently submitted by Nic Lewis and some others, where he sharply lowers the sensitivity ranges based on the last decade of data - and others dispute his claims. He also has been complaining about the use of uniform priors in earlier IPCC estimates, so that part of the lecture is really very relevant!
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