Future Impact of Differential Interbasin Ocean Warming on Atlantic Hurricanes

Global climate model simulations forced by future greenhouse warming project that the tropical North Atlantic (TNA) warms at a slower rate than the tropical Indo-Pacific in the twenty-first century, consistent with their projections of a weakened Atlantic thermohaline circulation. Here, an atmospheric general circulation model is used to advance a consistent physical rationale that the suppressed warming of the TNA increases the vertical wind shear and static stability aloft in the main development region (MDR) for Atlantic hurricanes, and thus decreases overall Atlantic hurricane activity in the twenty-first century. A carefully designed suite of model experiments illustrates that the preferential warming of the tropical Indo-Pacific induces a global average warming of the tropical troposphere, via a tropical teleconnection mechanism, and thus increases atmospheric static stability and decreases convection over the suppressed warming region of the TNA. The anomalous diabatic cooling, in turn, forces the formation of a stationary baroclinic Rossby wave northwest of the forcing region, consistent with Gill’s simple model of tropical atmospheric circulations, in such a way as to induce a secular increase of the MDR vertical wind shear. However, a further analysis indicates that the net effect of future greenhouse warming on the MDR vertical wind shear is less than the observed multidecadal swing of the MDR vertical wind shear in the twentieth century. Thus, it is likely that the Atlantic multidecadal oscillation will still play a decisive role over the greenhouse warming in the fate of Atlantic hurricane activity throughout the twenty-first century under the assumption that the twenty-first-century changes in interbasin SST difference, projected by the global climate model simulations, are accurate.