How much will the global water cycle accelerate with global warming? In a recent study, Wentz et al.  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.