Abstract

Abstract Equilibrium climate sensitivity, the global surface temperature response to CO doubling, has been persistently uncertain. Recent consensus places it likely within 1.5–4.5 K. Global climate models (GCMs), which attempt to represent all relevant physical processes, provide the most direct means of estimating climate sensitivity via CO quadrupling experiments. Here we show that the closely related effective climate sensitivity has increased substantially in Coupled Model Intercomparison Project phase 6 (CMIP6), with values spanning 1.8–5.6 K across 27 GCMs and exceeding 4.5 K in 10 of them. This (statistically insignificant) increase is primarily due to stronger positive cloud feedbacks from decreasing extratropical low cloud coverage and albedo. Both of these are tied to the physical representation of clouds which in CMIP6 models lead to weaker responses of extratropical low cloud cover and water content to unforced variations in surface temperature. Establishing the plausibility of these higher sensitivity models is imperative given their implied societal ramifications.

Keywords

Coupled model intercomparison projectExtratropical cycloneClimate sensitivityClimatologyClimate modelCloud feedbackEnvironmental scienceCloud coverAlbedo (alchemy)Sensitivity (control systems)Atmospheric sciencesClimate changeMeteorologyCloud computingGeologyComputer scienceGeography

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Publication Info

Year
2020
Type
article
Volume
47
Issue
1
Citations
1678
Access
Closed

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Mark D. Zelinka, Timothy A. Myers, Daniel T. McCoy et al. (2020). Causes of Higher Climate Sensitivity in CMIP6 Models. Geophysical Research Letters , 47 (1) . https://doi.org/10.1029/2019gl085782

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DOI
10.1029/2019gl085782

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Data completeness: 81%