Global precipitation response to changing forcings since 1870

Predicting and adapting to changes in the hydro- logical cycle is one of the major challenges for the 21st cen- tury. To better estimate how it will respond to future changes in climate forcings, it is crucial to understand how the hy- drological cycle has evolved in the past and why. In our study, we use an atmospheric global climate model with pre- scribed sea surface temperatures (SSTs) to investigate how, in the period 1870-2005, changing climate forcings have affected the global land temperature and precipitation. We show that between 1870 and 2005, prescribed SSTs (encap- sulating other forcings and internal variability) determine the decadal and interannual variabilities of the global land tem- perature and precipitation, mostly via their influence in the tropics (25 S-25 N). In addition, using simulations with prescribed SSTs and considering the atmospheric response alone, we find that between 1930 and 2005 increasing aerosol emissions have reduced the global land temperature and pre- cipitation by up to 0.4 C and 30 mm yr 1 , respectively, and that between about 1950 and 2005 increasing greenhouse gas concentrations have increased them by up to 0.25 C and 10 mm yr 1 , respectively. Finally, we suggest that be- tween about 1950 and 1970, increasing aerosol emissions had a larger impact on the hydrological cycle than increas- ing greenhouse gas concentrations.