Abstract Methane is the third most significant anthropogenic driver of climate change after carbon dioxide and aerosols, contributing about one-fourth of carbon dioxide’s effective radiative forcing in the industrial era. Given the role of methane in observed and future climate change, this study compares the slow climate responses to carbon dioxide (CO 2 ) and methane (CH 4 ) radiative forcings by estimating individual climate feedbacks using radiative kernels. We use the National Centre for Atmospheric Research (NCAR) Community Atmosphere Model (CAM5) in two configurations (prescribed sea surface temperature and slab ocean) to estimate radiative forcing and climate response, respectively. These experiments show that for comparable radiative forcing, methane forcing’s efficacy in the 10XCH 4 experiment (0.90) is smaller than the efficacy of 1.35XCO 2 (unity), consistent with previous studies. This lower efficacy of the slow response for CH 4 owing to its more negative feedback (−1.08 W m −2 K −1 ) compared to CO 2 (−0.97 W m −2 K −1 ) is attributed to differences in lapse rate, water vapor, shortwave cloud, and albedo feedbacks. Despite the broadly similar meridional distributions of radiative forcing, methane’s larger longwave and shortwave forcing in tropical latitudes give rise to significant differences in lapse rate and cloud feedbacks, resulting in smaller climate sensitivity than CO 2 forcing. CH 4 also has smaller albedo feedback, owing to its atmospheric absorption of shortwave radiation.
Kumar et al. (Fri,) studied this question.