Present-day methane shortwave absorption mutes surface warming relative to preindustrial conditions

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http://eprints.org/relation/isVersionOf https://pure.iiasa.ac.at/id/document/107763 http://eprints.org/relation/isVolatileVersionOf https://pure.iiasa.ac.at/id/document/107763 http://eprints.org/relation/issmallThumbnailVersionOf https://pure.iiasa.ac.at/id/document/107763 archive 353 disk0/00/02/00/66 2024-10-23 07:09:43 2024-10-23 07:39:00 2024-10-23 07:09:43 article show Allen R.J. Zhao X. Randles C.A. Kramer R.J. Samset B.H. Smith C. 9291 0000-0003-0599-4633 Present-day methane shortwave absorption mutes surface warming relative to preindustrial conditions pub ECE IACC 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. Our results corroborate the hypothesis that present-day methane shortwave absorption mutes the warming effects of longwave absorption. For example, the global mean cooling in response to the present-day methane shortwave absorption is -0.10±0.07 K, which offsets 28 % (7 %-55 %) of the surface warming associated with present-day methane longwave radiative effects. The precipitation increase associated with the longwave radiative effects of the present-day methane perturbation (0.012±0.006 mm d-1) is also muted by shortwave absorption but not significantly so (-0.008±0.009 mm d-1). The unique responses to methane shortwave absorption are related to its negative top-of-the-atmosphere effective radiative forcing but positive atmospheric heating and in part to methane's distinctive vertical atmospheric solar heating profile. We also find that the present-day methane shortwave radiative effects, relative to its longwave radiative effects, are about 5 times larger than those under idealized carbon dioxide perturbations. Additional analyses show consistent but non-significant differences between the longwave versus shortwave radiative effects for both methane and carbon dioxide, including a stronger (negative) climate feedback when shortwave radiative effects are included (particularly for methane). We conclude by reiterating that methane remains a potent greenhouse gas. 2024-10-09 published European Geosciences Union (EGU) doi:10.5194/acp-24-11207-2024 3162 public Atmospheric Chemistry and Physics 24 19 11207-11226 TRUE 1680-7324 no info:eu-repo/semantics/article