Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Gavin's proclamation that the earth's sensitivity lies around 3.3 degrees C, discussion about that figure is far from over.

Err, no ... what he actually wrote was (reply to comment #1 at link to RealClimate):

We can even go one step further - what climate sensitivity would have given a perfect forecast given the actual (as opposed to projected) forcings? The answer is 3.3 deg C for a doubling of CO2.

So the 3.3 deg C is a retrospective determination of the value that would have (does) give the best agreement between the 1988 model and the current observations. As such, discussion about that precise figure is over. It is a cold, hard mathematical fact (unless he made an error in running the calculation). Even future measurements do not change this value, because it is specifically an evaluation of an old model against the data available as of early 2011.

A more appropriate comment regarding current opinion on the value for climate sensitivity is in the body of the post:

... and the old GISS model had a climate sensitivity that was a little higher (4.2ºC for a doubling of CO2) than the best estimate (~3ºC).

"best estimate" and "~" acknowledge uncertainty and do not indicate a belief that discussion is over.

by det on Tue Feb 8th, 2011 at 03:42:16 AM EST
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