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Old 06-04-2013, 11:09 AM
Michael Reach Michael Reach is offline
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Join Date: Apr 2013
Location: Baltimore, Maryland, USA
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Default Re: Data snooping and science

Elroch, I think you are mistaken. Certainly the wikipedia article doesn't discuss the point. Here's a place that does
"Tuning the climate of a global model"
http://onlinelibrary.wiley.com/doi/1...12MS000154/pdf
Note that the paper says that this model didn't need much tuning (still had some, though) because it was based on an earlier model that was carefully tuned to fit the 20th century data. This quote:
"Climate models ability to simulate the 20th century temperature increase with fidelity has become something of a show-stopper as a model unable to reproduce the 20th century would probably not see publication, and as such it has effectively lost its purpose as a model quality measure."

I think it is clear that none of the models are "purely physical" in the sense you mean. There are many models, and they make many choices, and they are constrained ("tuned") by the requirement that they must fit 20th century data. All those choices lead to different predictions and different sensitivities to CO2. I don't understand how one can claim that the choices are minor, when they lead to a range of several degrees C in their predictions (Figure 1 is very striking), as the paper points out. As such, overfitting is a potential issue, and Bayesian statistics should be usable to decide between them afterwards.
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