There is a debate about climate sensitivity (CS) over on the blog of James Annan, an excellent climatologist. He has been agreeing that recent work makes it less likely that the highest values of climate sensitivity (i.e the notion that a doubling of CO2 levels will lead to temperature increases of more than 4C, going right up to 10C in some studies) are to be expected.
James' statement has caused great excitement in the climate sceptics' camp. On the other hand, I am pleased at the convergence of lower CS from climatologists, and a realisation on the part of "lukewarmer" climate skeptics that they must put forward a figure for CS. Because their figure overlaps with the climatologists' figure, and the point of overlap is highly significant in terms of policy.
Here is the comment I put up (number 100 in the comments, which began 4 days ago):
Could it be that we are missing something very important in this debate on the minutiae of the CS figure, and that is, that the climate controversy is now over, as far as policy is concerned?
By this, I mean that luke-warmers, when pressed for a 90% confidence figure for CS will usually give a value between 1.2C and 2.4C.
In giving this, they are stating that it is likely that if we continue business as usual up to 2050, the planet is going to cross the 2C increase threshold at some point in the future, and that 2C threshold has been set as something to be avoided.
Of course, some lukewarmers will then begin to argue that the effects of a 2C increase have been wrongly forecast on the alarmist side, or that the precautionary principle can be set aside.
On the other hand, other lukewarmers may well agree that we should continue with the decarbonisation programme that is already started in many enlightened countries and localities.
This is not to call an end to the fun for the climatologists. There is still plenty to argue about, as this comment list demonstrates, but as far as policy goes, someone should tell the policy makers the good news that the reasonable climate skeptics are now on side.