Cloud Feedbacks, Rapid Adjustments, and the Forcing-Response Relationship in a Transient CO2Reversibility Scenario

AbstractThe Hadley Centre Global Environment Model, version 2–Earth System (HadGEM2-ES) climate model is forced by a 1% yr−1 compound increase in atmospheric CO2 for 140 years, followed by a 1% yr−1 CO2 decrease back to the starting level. Analogous atmosphere-only simulations are performed to diagnose the component of change associated with the effective radiative forcing and rapid adjustments. The residual change is associated with radiative feedbacks that are shown to be linearly related to changes in global-mean surface air temperature and are found to be reversible under this experimental design, even for regional cloud feedback changes. The cloud adjustment is related to changes in cloud amount, with little indication of any large-scale changes in cloud optical depth. Plant physiological forcing plays a significant role in determining the cloud adjustment in this model and is the dominant contribution to the low-level cloud changes over land. Low-level cloud adjustments are associated with changes i...

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