Muted extratropical low cloud seasonal cycle is closely linked to underestimated climate sensitivity in models

Xianan Jiang; Hui Su; Jonathan H Jiang; J David Neelin; Longtao Wu; Yoko Tsushima; Gregory Elsaesser

doi:10.1038/s41467-023-41360-0

Muted extratropical low cloud seasonal cycle is closely linked to underestimated climate sensitivity in models

Nat Commun. 2023 Sep 11;14(1):5586. doi: 10.1038/s41467-023-41360-0.

Authors

Xianan Jiang^{1

2}, Hui Su^{3

4

5}, Jonathan H Jiang⁶, J David Neelin⁵, Longtao Wu⁶, Yoko Tsushima⁷, Gregory Elsaesser⁸

Affiliations

¹ Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, Los Angeles, CA, USA. xianan@ucla.edu.
² Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA. xianan@ucla.edu.
³ Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, Los Angeles, CA, USA.
⁴ Department of Civil and Environmental Engineering, Hong Kong University of Science and Technology, Hong Kong, China.
⁵ Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, Los Angeles, CA, USA.
⁶ Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA.
⁷ Met Office Hadley Centre, Exeter, UK.
⁸ NASA Goddard Institute for Space Studies, and Department of Applied Physics and Mathematics, Columbia University, New York, NY, USA.

Abstract

A large spread in model estimates of the equilibrium climate sensitivity (ECS), defined as the global mean near-surface air-temperature increase following a doubling of atmospheric CO₂ concentration, leaves us greatly disadvantaged in guiding policy-making for climate change adaptation and mitigation. In this study, we show that the projected ECS in the latest generation of climate models is highly related to seasonal variations of extratropical low-cloud fraction (LCF) in historical simulations. Marked reduction of extratropical LCF from winter to summer is found in models with ECS > 4.75 K, in accordance with the significant reduction of extratropical LCF under a warming climate in these models. In contrast, a pronounced seasonal cycle of extratropical LCF, as supported by satellite observations, is largely absent in models with ECS < 3.3 K. The distinct seasonality in extratropical LCF in climate models is ascribed to their different prevailing cloud regimes governing the extratropical LCF variability.

Abstract

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