Does the Last Glacial Maximum constrain climate sensitivity?

Four simulations with atmosphere-ocean climate models have been produced using identical Last Glacial Maximum ice sheets, topography and greenhouse gas concentrations. Compared to the pre-industrial, the diagnosed radiative feedback parameter ranges between - 1.30 and - 1.18 Wm(-2)K(-1), the tropical ocean sea-surface temperature decreases between 1.7 and 2.7 degrees C, and Antarctic surface air temperature decreases by 7 to 11 degrees C. These values are all compatible with observational estimates, except for a tendency to underestimate the tropical ocean cooling. On the other hand, the same models have a climate sensitivity to CO2 concentration doubling ranging between 2.1 and 3.9 K. It is therefore inappropriate to simply scale an observational estimate of LGM temperature to predict climate sensitivity. This is mainly a consequence of the non-linear character of the cloud ( mainly shortwave) feedback at low latitudes. Changes in albedo and cloud cover at mid and high latitudes are also important, but less so.