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Abstract
Equilibrium climate sensitivity (ECS) and hydrological sensitivity describe the global mean surface temperature and precipitation responses to a doubling of atmospheric CO2. Despite their connection via the Earth’s energy budget, the physical linkage between these two metrics remains controversial. Here, using a global climate model with a perturbed mean hydrological cycle, we show that ECS and hydrological sensitivity per unit warming are anti-correlated owing to the low-cloud response to surface warming. When the amount of low clouds decreases, ECS is enhanced through reductions in the reflection of shortwave radiation. In contrast, hydrological sensitivity is suppressed through weakening of atmospheric longwave cooling, necessitating weakened condensational heating by precipitation. These compensating cloud effects are also robustly found in a multi-model ensemble, and further constrained using satellite observations. Our estimates, combined with an existing constraint to clear-sky shortwave absorption, suggest that hydrological sensitivity could be lower by 30% than raw estimates from global climate models.
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; Kamae, Youichi 2
; Shiogama, Hideo 3
; DeAngelis, Anthony M 4 ; Suzuki, Kentaroh 1 1 Atmosphere and Ocean Research Institute, University of Tokyo, Tokyo, Japan
2 Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan; Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, USA
3 Center for Global Environmental Research, National Institute for Environmental Studies, Tsukuba, Japan
4 Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD, USA; Science Systems and Applications, Lanham, MD, USA