The role of oceanic feedback and air-sea interaction in the climate response to greenhouse gas warming

Two suites of partial coupling experiments are devised with the upper ocean dynamics version (UOM) of the CCSM3 to isolate the effects of the feedbacks from the changed wind-driven ocean circuation and air-sea interaction in the global climate response to the forcing of doubling CO2. The partial coupling is achieved by implementing a so-called overriding technique, which helps quantitatively partition the total response in the fully coupled model to the feedback component in question and the response to external forcing in the absence of the former. By overriding the wind stress that is the momentum driving for the ocean and the wind speed used in the bulk formula for evaportaion, the experiments help to reveal (i) the weakened tropical Pacific wind may not be responsible for the El Niño-like SST warming as previously speculated from the thermocline and Bjerknes feedback; (ii) the wind-evaporation-SST (WES) feedback is the main formation mechanism for the tropical SST pattern under the CO2 forcing, verifying the hypothesis proposed by Xie et al. (2010); (iii) WES is also the leading mechanism for shaping the tropical precipitation response in the ocean; (iv) Both the wind-driven ocean dynamical feedback and the WES feedback act to increase the persistence of the Southern Annular mode (SAM), and the increased time scale of the SAM due to these feedbacks manifests itself in the response of the jet shift to an identical CO2 forcing, in a manner conforming to the fluctuation-dissipation theorem.