Hysteresis of global atmospheric rivers to carbon dioxide removal

Atmospheric rivers (ARs) are key agents regulating global hydroclimate and extreme precipitation. Climate models project the increase and intensification of ARs in a warming climate, but their responses to CO₂ mitigation remain unclear. Based on large-ensemble climate model experiments in which CO₂ concentrations are systematically increased and then decreased to the present-day levels, we show that AR frequency and intensity do not fully return to their present-day states when CO₂ concentrations are reduced. Instead ARs are projected to become more frequent and intense after CO₂ removal, particularly along the western coasts of North America, Europe and South America, in East Asia, and along the Antarctic coast, leading to increased extreme precipitation in the midlatitudes and potential threat to Antarctic ice shelf stability. These hysteretic responses of ARs are attributed to both thermodynamic and dynamic changes that manifest differently by region but are closely related to the delayed recovery of the Atlantic meridional overturning circulation and the Southern Ocean temperature.