Pedro DiNezio, University of Miami/RSMAS
Abstract: I will present a theory for tropical Pacific climate change and apply it to interpret climate model experiments of future anthropogenic global warming (AGW) and the Last Glacial Maximum (LGM). The response of the tropical-mean hydrological cycle to warming (cooling) constrains the Walker circulation to weaken (strengthen) consistently in all models. However, unlike during El Niño or La Niña events, when the ocean amplifies changes in the Walker circulation; during climate change, ocean dynamics oppose the changes in the atmospheric circulation. This occurs because the on longer time scales the response of the equatorial thermocline to changes in the winds decouples the positive feedback loop between winds and SST, i.e. the Bjerknes feedback. In both AGW and LGM experiments, the response results from several opposing mechanisms, explaining why the tropical Pacific does not become either El Niño- or La Niña-like, but also suggesting that the tropical Pacific is more stable to external forcing than proposed by previous theories. To conclude, I will present ideas for detection and attribution of these mechanisms in observations and proxies.