Higher precipitation in East Asia and western United States expected with future Southern Ocean warming

Precipitation over East Asia and the western United States is projected to increase as a result of global warming, although substantial uncertainties persist regarding the magnitude. A key factor driving these uncertainties is the tropical surface warming pattern, yet the mechanisms behind both this warming pattern and the resulting regional precipitation changes remain elusive. Here we use a set of climate model experiments to argue that these changes are partly driven by global teleconnection from the Southern Ocean, which rapidly absorbs anthropogenic heat but releases it with a delay of decades to a century. We show that the delayed Southern Ocean warming contributes to broad tropical ocean warming with an El Niño-like pattern, enhancing precipitation during summer in East Asia and winter in the western United States. The atmospheric teleconnections from the tropical ocean link the Southern Ocean warming to the Northern Hemisphere regional wetting. Southern Hemisphere low clouds are a key regulator of this teleconnection, partly explaining the projected uncertainty of regional precipitation. The documented teleconnection has practical implications: even if climate mitigation reduces carbon dioxide levels, the delayed Southern Ocean warming will sustain a wetter East Asia and western United States for decades to centuries.