Global impacts of recent Southern Ocean cooling

Since the beginning of the satellite era, Southern Ocean sea surface temperatures (SSTs) have cooled, despite global warming. While observed Southern Ocean cooling has pre-viously been reported to have minimal impact on the tropical Pacific, the efficiency of this teleconnection has recently shown to be mediated by subtropical cloud feedbacks that are highly model-dependent. Here, we conduct a coupled model intercomparison of paired ensemble simulations under historical radiative forcing: one with freely evolving SSTs and the other with Southern Ocean SST anomalies constrained to follow observa-tions. We reveal a global impact of observed Southern Ocean cooling in the model with stronger (and more realistic) cloud feedbacks, including Antarctic sea-ice expansion, southeastern tropical Pacific cooling, northward-shifted Hadley circulation, Aleutian low weakening, and North Pacific warming. Our results therefore suggest that observed Southern Ocean SST decrease might have contributed to cooler conditions in the eastern tropical Pacific in recent decades.

Automated summary

Since the satellite era, Southern Ocean sea surface temperatures (SSTs) have been cooling despite global warming. Recent studies have shown that the impact of Southern Ocean cooling on the tropical Pacific is mediated by subtropical cloud feedbacks, which depend on the model used. In our study, we conduct a coupled model intercomparison and reveal a global impact of observed Southern Ocean cooling, including sea-ice expansion in Antarctica, cooling in the southeastern tropical Pacific, northward shift of the Hadley circulation, weakening of the Aleutian low, and warming in the North Pacific. These findings suggest that the observed Southern Ocean cooling may have contributed to cooler conditions in the eastern tropical Pacific in recent decades.