Muted Radiative Feedback of Stratospheric Water Vapor Found in a Multimodel Assessment

Abstract The strength of stratospheric water vapor (SWV) radiative feedback has been debated, primarily due to the compensating radiative effects of the associated stratospheric and tropospheric temperature adjustments, which are primarily triggered by radiation process. In this study, we calculate the SWV radiative feedback in the CMIP6 model ensemble in a quadrupling CO 2 experiment. Specifically, we compare the results of two quantifications: one accounting for the radiatively driven temperature adjustment in the stratosphere only and the other in the entire atmospheric column including both the stratosphere and the troposphere. The stratosphere‐adjusted feedback is found to be , but it reduces to with the full atmosphere adjustment, indicating the radiation process alone may lead to a muted overall SWV radiative effect, due to the stratospheric cooling and tropospheric warming simultaneously driven by the SWV radiative perturbation. This suggests that the radiative forcing of SWV is subject to an intrinsic and robust limiting effect. In addition, we analyze the intermodel spreads in the temperature adjustment and its radiative effect, and find the spreads primarily arise from the differences in SWV responses projected by GCMs, rather than the differences in their climatological states.