Increasing Potential for Intense Tropical and Subtropical Thunderstorms Under Global Warming

Climate models project large future increases in the summertime-mean convective available potential energy (CAPE) in most tropical and subtropical regions. However, the physical mechanisms leading to such increases, and the implications for thunderstorm activity, remain uncertain. Here, we focus on high percentiles of the CAPE distribution (CAPE extremes) as a measure of thunderstorm potential, and we show that CAPE extremes also increase robustly with warming across the tropics and subtropics in an ensemble of state-of-the-art global climate models (GCMs) and in a ``superparameterized'' GCM that includes an explicit representation of convection within each model grid column.

The simulated CAPE increases are consistent with a recently-proposed theory which states that CAPE is determined by the effect of convective entrainment on the tropospheric lapse rate. We demonstrate the importance of this effect for simulated CAPE extremes using a GCM in which the convective entrainment rate is varied. Furthermore, we show that the theory accounts for the climatological relationship between CAPE and a measure of lower-tropospheric humidity in simulations and in observations. Our results suggest a physical basis on which to understand projected increases in tropical and subtropical thunderstorm potential, and they provide evidence that an important mechanism that contributes to such increases is present in Earth's atmosphere.