Present-Day Methane Shortwave Absorption Mutes Surface Warming and Wetting Relative to Preindustrial Conditions

Abstract. Recent analyses show the importance of methane shortwave absorption, which many climate models lack. In particular, Allen et al. (2023) used idealized climate model simulations to show that methane shortwave absorption mutes up to 30 % of the surface warming and 60 % of the precipitation increase associated with its longwave radiative effects. Here, we explicitly quantify the radiative and climate impacts due to shortwave absorption of the present-day methane perturbation using the Community Earth System Model version 2. Our results corroborate that present-day methane shortwave absorption mutes the warming and wetting effects of longwave absorption. For example, the global mean cooling in response to the present-day methane shortwave absorption is -0.10 ± 0.04 K, which offsets 29 % of the surface warming associated with present-day methane longwave radiative effects. Similarly, we explicitly estimate 66 % of the precipitation increase associated with the longwave radiative effects of the present-day methane perturbation is offset by shortwave absorption. Unlike other solar absorbers (i.e., black carbon), the decrease in global mean precipitation under methane shortwave absorption is driven by both fast (atmospheric absorption) and slow (surface temperature cooling) responses. Finally, we show that the present-day methane shortwave radiative effects, relative to its longwave radiative effects, are about five times larger as compared to those under idealized carbon dioxide perturbations. The unique responses to methane shortwave absorption are related to its vertical atmospheric solar heating profile. Methane remains a potent greenhouse gas and continued endeavors to decrease methane emissions are necessary to stay below the 1.5 °C global warming threshold.