A113-0006
Cloud Feedbacks from CanESM2 to CanESM5 and their Influence on Climate Sensitivity

Friday, 11 December 2020
Poster
John Virgin1, Christopher G Fletcher1, Jason N Cole2, Knut von Salzen3 and Toni Mitovski4, (1)University of Waterloo, Waterloo, ON, Canada, (2)Environment Canada Toronto, Toronto, ON, Canada, (3)CCCma, Environment and Climate Change Canada, Victoria, BC, Canada, (4)Environment Canada Toronto, Climate Research Division, Toronto, ON, Canada
Abstract:
The newest iteration of the Canadian Earth System Model (CanESM5) has an effective climate sensitivity (ECS) of 5.65 kelvin, which is a 54% increase relative to the model's previous version (CanESM2 - 3.67K), and the highest sensitivity of all current models participating in the sixth generation of the coupled model inter-comparison project (CMIP6). Here, we explore the underlying causes and model developments behind CanESM5's increased ECS via comparison of forcing and feedbacks between CanESM2 and CanESM5. Through the use of cloud area fraction output and radiative kernels, we find that more positive shortwave cloud feedbacks- particularly with regards to low cloud amount over eastern ocean basins and subtropical high cloud optical depth- are the dominant contributors to CanESM5's increased climate sensitivity. We attribute the change in shortwave cloud feedbacks, at least in part, to a new autoconversion parametrization scheme that has been implemented in CanESM5 in order to improve the model's representation of aerosol-cloud interactions. Our results highlight the recent trend of CMIP6 models with high ECS and their respective causes being tied to improved physical representation of clouds.
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