Emergent Constraint on Future Changes in the Tropical Atmospheric Circulation

Intensification of the hydrological cycle manifests through a global increase in precipitation at a rate lower than the increase in water vapor, and a consequent weakening in the atmospheric tropical overturning circulation (ATOC). This circulation change shapes future precipitation patterns, but is highly uncertain across Earth System Models (ESMs), complicating efforts seeking to constrain projected changes in regional precipitation. Using two ESM ensembles, we present an emergent relationship between the ATOC’s response to anthropogenic warming, and the ATOC’s variability associated with interannual temperature anomalies. Models simulating the largest future ATOC weakening per degree warming also tend to simulate the largest weakening in association with an internally-generated warm anomaly. Observational estimates of ATOC sensitivity suggest that future ATOC weakening due to climate change is likely larger than expected from a simple multimodel mean (from -1.41±1.06 %/K to -2.20±0.93 %/K). Lastly, we show how this enhanced ATOC weakening impacts regional precipitation patterns. These constrained circulation and precipitation estimates provide a better understanding of how tropical hydroclimate will respond to future warming and associated regional climate impacts.