• climate change;
  • rainfall;
  • SST;
  • tropics

Mechanisms behind regional tropical rainfall responses to CO2 forcing are examined in idealized climate model experiments, traceable to transient forcing scenarios. As previously shown, the pattern of the first-year response of dynamical precipitation change to an abrupt CO2 increase is similar to the century-scale response. It is demonstrated here that this similarity is driven by surface temperature pattern change, not a direct atmospheric circulation response to CO2. This confirms the “Warmer get Wetter” hypothesis, which emphasizes the role of sea surface temperature pattern change in driving regional tropical precipitation change. Future regional rainfall changes should thus be studied primarily in coupled ocean-atmosphere models.