• Open Access

Tropical precipitation and convection changes in the Max Planck Institute Earth system model (MPI-ESM) in response to CO2 forcing


Corresponding author: T. Crueger, Max Planck Institute for Meteorology, Bundesstrasse 53, D-20146 Hamburg, Germany. (traute.crueger@zmaw.de)


[1] In this study, the sensitivity of tropical precipitation and convection to CO2 forcing is examined. In order to test the robustness of the response, two simulations with idealized CO2 forcings following CMIP5, one with a smooth and one with an abrupt CO2 increase, are analyzed. The simulations are performed with the Max Planck Institute Earth system model (MPI-ESM). Beyond investigating the mean precipitation response, high-frequency (30 min) direct output of the convection scheme is considered to better assess the ability of the convection scheme to reproduce results from cloud-resolving simulations or physical argumentation. Over the tropics, precipitation increases by 1.7% K−1 almost independently of the CO2 forcing. Over land, the response under transient CO2 forcing is also positive, but negative under an abrupt CO2 increase. In both cases precipitation tends to follow evaporation, but the latter reacts differently due to land surface processes. The Madden-Julian oscillation also shows different sensitivities for the two CO2 forced climates. As the climate warms, deep convection gets more intense, less frequent, and deeper. The cloud top temperatures remain constant, whereas cumulus congestus and shallow clouds warm. As such, the MPI-ESM and its convection scheme hold for the fixed-anvil temperature hypothesis. This implies an enhancement of the deep convective cloud height by 3–4% K−1. Changes in precipitation intensity and convective cloud base properties scale with the Clausius-Clapeyron equation, whereas the energy constraint determines changes in precipitation frequency. This is true over the tropics considered as a whole and over the tropical oceans, but breaks down over land.