Interdecadal Variability of Rainfall on a Warming Planet

How much will the global water cycle accelerate with global warming? In a recent study, Wentz et al. 2007 used satellite observations to show that global mean precipitation increased by 7% per °C increase in global mean surface temperature over the period between July 1987 and August 2006. This yields an absolute precipitation increase of 13.2±4.8 millimeters per year per decade, a rate of increase that is 2–3 times greater than that simulated by general circulation models (GCMs). Century‐long integrations of GCMs also yield much smaller global precipitation increases of about 1–3% per °C of global warming Held and Soden , 2006. Nonetheless, Wentz et al. 2007, p. 235 argue that the recent 20‐year period may “be long enough to indicate that the observed scaling relations e.g., between precipitation and temperature will continue on a longer time scale,” implying significant errors in climate model predictions.