Hydrologic Cycle Weakening in Hothouse Climates

TL;DR

This study uses climate models to show that in hothouse climates, the hydrologic cycle initially intensifies with warming but weakens beyond a certain temperature, affecting planetary climate evolution.

Contribution

It reveals a non-monotonic response of the hydrologic cycle to extreme warming, a phenomenon robust across various model configurations and planetary conditions.

Findings

Precipitation increases then decreases with temperature in models.

Weakening linked to limits on outgoing longwave radiation and water vapor absorption.

Implications for Earth's future and exoplanet habitability.

Abstract

The hydrologic cycle has wide impacts on the ocean salinity and circulation, carbon and nitrogen cycles, and the ecosystem. Under anthropogenic global warming, previous studies showed that the intensification of the hydrologic cycle is a robust feature. Whether this trend persists in hothouse climates, however, is unknown. Here we show in climate models that mean precipitation first increases with rising surface temperature, but the precipitation trend reverses when the surface is hotter than ~320-330 K. This non-monotonic phenomenon is robust to the cause of warming, convection scheme, ocean dynamics, atmospheric mass, planetary rotation, gravity, and stellar spectrum. The weakening occurs because of the existence of an upper limitation of outgoing longwave emission and the continuously increasing shortwave absorption by H2O, and is consistent with atmospheric dynamics featuring the strong increase of atmospheric stratification and dramatic reduction of convective mass flux. These results have wide implications for the climate evolutions of Earth, Venus, and potentially habitable exoplanets.