Eastern equatorial Pacific warming delayed by aerosols and thermostat response to CO2

Abstract Understanding the tropical Pacific response to global warming remains a challenging problem. Here, we assess the recent and future evolution of the equatorial Pacific east-west temperature gradient, and the Walker circulation, across a range of different greenhouse warming experiments within the CMIP6 dataset. In abrupt CO2-increase scenarios many models generate an initial strengthening of this gradient resembling an ocean thermostat (OT), followed by a small weakening; other models generate an immediate weakening that becomes progressively larger establishing a pronounced eastern equatorial Pacific (EP) warming pattern. The initial response in these experiments is a very good predictor for the future EP pattern simulated in both abrupt and realistic warming scenarios, but not in historical simulations showing no multi-model trend. The likely explanation is that recent CO2-driven changes in the tropical Pacific are masked by aerosol effects, and a potential OT delay, while the EP warming pattern will emerge as greenhouse gases overcome aerosol forcing.