Global anthropogenic aerosol effects on convective clouds in ECHAM5-HAM

Aerosols affect the climate system by changing cloud characteristics in many ways. They act as cloud condensation and ice nuclei and may have an influence on the hydrological cycle. Here we investigate aerosol effects on convective clouds by extending the double moment cloud microphysics scheme developed for stratiform clouds to convective clouds in the ECHAM5 general circulation model. This increases the liquid water path in the tropics and reduces the sensitivity of the liquid water path with increasing aerosol optical depth in better agreement with observations and large-eddy simulation studies. In simulations in which greenhouse gases and aerosols emissions are increased since pre-industrial times, accounting for microphysics in convective clouds matches most closely the observed increase in precipitation. The total anthropogenic aerosol effect since pre-industrial time is slightly reduced from 1.6 to 1.9 W m 2 when microphysics are only included in stratiform clouds to 1.5 W m 2 when microphysics are included both in stratiform and convective clouds.