Clear-sky control of anvils in response to increased CO2 or surface warming or volcanic eruptions

Abstract

Anvil clouds produced by deep convection cover extensive areas of the tropics, and their response to external perturbations matters for the Earth’s climate sensitivity. It has been suggested that variations in the height and spatial extent of these clouds can be understood from basic physical arguments related to the conservation of mass and energy in the clear-sky areas of the tropics. Based on satellite observations, meteorological reanalyses, and climate model simulations, we show that these arguments can be used to interpret the response of anvil cloud fraction to a range of perturbations in the current climate and under climate change. This includes the response to interannual and long-term surface temperature changes, to the direct effect of carbon dioxide, and the decrease of anvil cloud fraction after explosive volcanic eruptions. Therefore, the control of tropical anvils by clear-sky radiative cooling and static stability in the upper troposphere can explain a large diversity of the responses of anvil cloud fraction to natural and anthropogenic perturbations. These findings should also be considered when assessing the impacts of geo-engineering techniques.