Cloud Responses to Abrupt Solar and CO₂ Forcing: 2. Adjustment to Forcing in Coupled Models

In this paper, we examine differences in cloud adjustments (often called rapid adjustments) that occur as a direct result of abruptly increasing the solar constant by 4% or abruptly quadrupling of atmospheric CO 2 . In doing so, we devise a novel method for calculating the cloud adjustments for the abrupt solar forcing simulations that uses differences between coupled model simulations with abrupt solar and CO 2 forcing, in combination with uncoupled, atmosphere‐only, abrupt CO 2 forced experiments that have prescribed sea‐surface temperature. Our main findings are that (a) there are substantial differences in the responses of stratocumulus and cumulus clouds to solar and CO 2 forcing, which follow the differences in the direct radiative effect that solar and CO 2 forcing have at cloud top, and (b) there are differences in the adjustment of the average optical depth of high clouds to solar and CO 2 forcing that we speculate are driven by the differences in the vertical profile of radiative heating and differences in the pattern of sea‐surface temperature change (for a fixed global mean temperature). These cloud adjustments contribute significantly to the total net cloud radiative effect, even after 150 years of simulation.