The tropics and subtropics are home to some of the most intense thunderstorms on Earth. Such storms produce lightning, heavy precipitation, and, under certain conditions, damaging winds and hail. Understanding how intense thunderstorms may change in a future warmer climate is therefore crucial for assessing the likely impacts of climate change on human society. In this talk, I will show that a measure of the energy available to thunderstorms, the convective available potential energy (CAPE), increases robustly with warming across the tropics and subtropics in an ensemble of state-of-the-art climate models. Such increases in CAPE imply a greater frequency of environments conducive to damaging thunderstorms in future climate projections. To understand the physical mechanisms that lead to increased CAPE, I introduce a simple theoretical model for CAPE that incorporates the influence of entrainment on the tropospheric lapse rate. The theoretical model is consistent with the behaviour of CAPE in idealised cloud-resolving simulations and in climate-model simulations in which the convective entrainment rate is artificially varied. Furthermore, the theoretical model is able to account for the climatological relationship between CAPE and a measure of lower-tropospheric humidity in both simulations and in observations. The results suggest a physical basis on which to understand projected future increases in the potential for intense thunderstorms, and they provide evidence that an important mechanism that contributes to such increases is present in Earth’s atmosphere.
Intense tropical & subtropical thunderstorms in a warmer climate
The tropics and subtropics are home to some of the most intense thunderstorms on Earth. Such storms produce lightning, heavy precipitation, and, under certain conditions, damaging winds and hail. Understanding how intense thunderstorms may change in a future warmer climate is therefore crucial for assessing the likely impacts of climate change on human society. In this talk, I will show that a measure of the energy available to thunderstorms, the convective available potential energy (CAPE), increases robustly with warming across the tropics and subtropics in an ensemble of state-of-the-art climate models. Such increases in CAPE imply a greater frequency of environments conducive to damaging thunderstorms in future climate projections. To understand the physical mechanisms that lead to increased CAPE, I introduce a simple theoretical model for CAPE that incorporates the influence of entrainment on the tropospheric lapse rate. The theoretical model is consistent with the behaviour of CAPE in idealised cloud-resolving simulations and in climate-model simulations in which the convective entrainment rate is artificially varied. Furthermore, the theoretical model is able to account for the climatological relationship between CAPE and a measure of lower-tropospheric humidity in both simulations and in observations. The results suggest a physical basis on which to understand projected future increases in the potential for intense thunderstorms, and they provide evidence that an important mechanism that contributes to such increases is present in Earth’s atmosphere.