Instantaneous heating rate forcing differentiates tropical high-cloud adjustments across greenhouse gases

Abstract

Tropical high clouds are central to large-scale circulation and the hydrological cycle. The consensus expectation is that they rise and contract under surface warming, but their fast adjustment to greenhouse gas (GHG) concentrations is diverse. All GHGs reduce atmospheric longwave cooling, yet tropical high clouds can increase or decrease depending on the gas. Using a model hierarchy with unchanged sea surface temperature, we find increased tropical high cloud for CO2 and decreased tropical high cloud for CH4 and N2O. These diverging responses are primarily driven by changes in the vertical structure of upper-tropospheric radiative heating, with stratification changes playing a secondary role. This study reveals that instantaneous radiative forcing dominates upper tropospheric heating change, establishing a mechanistic link between the spectroscopy of specific GHGs and their cloud adjustments. These results highlight the importance of the vertical structure of radiative forcing beyond the conventional top-of-atmosphere metrics.