Tropospheric adjustment: The response of two general circulation models to a change in insolation

The responses of the HadSM3 and NCAR CCM3 general circulation models to a change in solar insolation are compared to their responses to a doubling of CO 2 concentration. In both models, it is found that the important difference is a rapid adjustment of the troposphere in the solar case that reduces the value of effective radiative forcing by about 25%. Clear‐sky warming appears to make the major contribution. Subsequent warming of the coupled troposphere, land‐surface, ocean mixed‐layer system occurs with a very similar sensitivity to that expected under a CO 2 forcing of the reduced value. Because of adjustment, the overall precipitation response to solar forcing is similar to, or less than the response to CO 2 forcing, despite being smaller per unit temperature change.