Indian Ocean Warming Trend Reduces Pacific Warming Response to Anthropogenic Greenhouse Gases: An Interbasin Thermostat Mechanism
A greater warming trend of sea surface temperature (SST) in the tropical Indian Ocean than that in the tropical Pacific is a robust feature found in various observational datasets. Yet, this interbasin warming contrast is not present in climate models. Here we investigate the impact of tropical Indian Ocean warming on the tropical Pacific response to anthropogenic greenhouse gas (GHG) warming by analyzing results from coupled model pacemaker experiments. We find that warming in the Indian Ocean induces local negative sea level pressure (SLP) anomalies, which extend to the western tropical Pacific, strengthening the zonal SLP gradient and easterly trades in the tropical Pacific. The enhanced trade winds reduce SST in the eastern tropical Pacific by increasing equatorial upwelling and evaporative cooling, which offset the GHG warming. This result suggests an interbasin thermostat mechanism, through which the Indian Ocean exerts its influence on the Pacific response to anthropogenic GHG warming.