Changes in the sea surface temperature threshold for tropical convection

Deep convection over tropical oceans is observed generally above a threshold for sea surface temperatures(1-4), which falls in the vicinity of 26-28 degrees C. High-resolution models suggest that the related sea surface temperature threshold for tropical cyclones rises in a warming climate(5,6). Some observations for the past few decades, however, show that tropical tropospheric warming has been nearly uniform vertically(7,8), suggesting that the troposphere may have become less stable and casting doubts on the possibility that the sea surface temperature threshold increases substantially with global warming. Here we turn to satellite observations of rainfall for the past 30 years. We detect significant covariability between tropical mean sea surface temperatures and the convective threshold on interannual and longer timescales. In addition, we find a parallel upward trend of approximately 0.1 degrees C/decade over the past 30 years in both the convective threshold and tropical mean sea surface temperatures. We conclude that, in contrast with some observational indications, the tropical troposphere has warmed in a way that is consistent with moist-adiabatic adjustment, in agreement with global climate model simulations.