Rapid Adjustments of Cloud and Hydrological Cycle to Increasing CO2: a Review

Abstract

Rapid cloud response to instantaneous radiative perturbation in the troposphere due to change in CO2 concentration is called cloud adjustment. Cloud adjustment develops on a short timescale because it is separated from surface temperature-mediated changes in cloud. Adjustments in cloud and tropospheric properties including the hydrological cycle have attracted considerable attention because of their importance in the interpretation of mechanisms of climate change and the identification of sources of uncertainty in climate sensitivity. Modeling studies have clearly revealed that major aspects of the tropospheric adjustment including the warming and drying of the troposphere, associated reduction of low cloud and increasing shortwave cloud radiative forcing, downward shift of the low-cloud layer, and slowdown of the global hydrological cycle, are common among many climate model simulations. Combinations of model simulations with realistic and idealized aqua-planet settings have helped demonstrate the roles of land and robust aspects of the tropospheric adjustment.