On the Correspondence Between Atmosphere‐Only and Coupled Simulations for Radiative Feedbacks and Forcing From CO 2

Abstract Atmosphere‐only experiments are widely used to investigate climate feedbacks simulated in more computationally expensive fully coupled global climate model simulations. We confirm that this remains a valid approach by comparing the radiative feedbacks and forcing between coupled and atmosphere‐only simulations for the latest models taking part in the 6th phase of the Coupled Model Intercomparison Project (CMIP6). For global‐mean cloud feedbacks, we find a better than previously known correspondence between these experiments, which applies even to the response of individual cloud properties (amount, altitude, and optical depth) and holds even when considering atmosphere‐only simulations of only 1 yr duration. For regional cloud feedbacks, the correspondence between the two experiments is generally present at every geographic location except for the tropical Pacific but takes longer experiments to reveal. For the lapse rate and surface albedo feedbacks, the correspondence between the two experiments is weaker due to the non‐uniform warming pattern and loss of sea ice in the coupled experiment. For the across‐model relationship between 4xCO 2 effective radiative forcing and feedback, we find a different behavior across experiments in CMIP6 than in CMIP5, casting doubt on the physical significance of previous results that highlighted an anti‐correlation between the two quantities. Overall, these results confirm the utility of atmosphere‐only experiments particularly to study cloud feedbacks, which are the dominant source of inter‐model spread in climate sensitivity.