Response of Tropical Precipitation to Global Warming

Using high-resolution cloud-resolving simulations with different CO(2) concentrations, local precipitation fluxes are found to obey Clausius-Clapeyron (CC) scaling. Previous studies of the effect of CO(2) concentration on precipitation extremes have used general circulation models, which are poor platforms for studying tropical convection because convection is parameterized. In idealized cloud-resolving simulations, it is possible to identify not only the changes in local precipitation fluxes, but also the factors responsible for those changes. There are many properties of convection that can change as the atmosphere warms, each of which could produce deviations from CC scaling. These properties include the effective water-vapor gradient, cloud pressure depth, and cloud velocity. A simple theory is developed that predicts the changes in these properties consistent with CC scaling. Convection in the cloud-resolving simulations is found to change as predicted by this theory, leading to an similar to 20% increase in local precipitation fluxes when the CO(2) concentration is doubled. Overall, an increase in CO(2) leads to more vigorous convection, composed of clouds that are wider, taller, and faster.