Observed Diurnal Cycle Change of Tropical Deep Convection Amplifies Surface Warming

Climate feedbacks from changes in the diurnal cycle of clouds have received limited attention. However, recent storm-resolving aquaplanet simulations predict a partial shift of tropical deep convection from daytime to nighttime in response to surface warming, producing a positive feedback of similar magnitude as other cloud feedbacks. Here, we use satellite observations of ice water path to test whether such a feedback exists. We use the internal variability within 24 years of observations to regress the diurnal cycle of cloud fraction against surface temperature. We find that clouds produced by deep convection partly shift from daytime to nighttime with increasing surface temperature, over both land and ocean. This increases the amount of solar radiation absorbed by the surface and hence constitutes a positive climate feedback. We derive a global feedback value of 0.12 ± 0.02 W m^-2 K^-1 for this diurnal-cycle feedback, which adds to previous estimates of the cloud feedback, implying a higher climate sensitivity.