Abstract
Climate sensitivity peaks around 310K in a wide variety of climate
models, ranging from idealized single column models to fully
comprehensive climate models. Although an explanation for this peak has
been developed using single column models with fixed relative humidity
and line-by-line radiation, the relevance of this theory for explaining
the peak in comprehensive climate models is unclear. In this paper we
increase CO2 using a clear-sky 3-dimensional climate model with a
radiation scheme that maintains accuracy for high CO2 and temperature
levels. The Equilibrium Climate Sensitivity (ECS) of our model shows a
plateau around 310K with the moistening of the subtropical regions
caused by a slowdown in atmospheric circulation increasing the ECS at
very high CO2 values. Though the changes in CO2 and temperature
presented here are extreme, this study shows the potential importance of
changes in atmospheric circulation and relative humidity in quantitative
assessments of climate sensitivity.