Distinct Changes in Tropical Cyclone Seasons Between the Western North Pacific and North Atlantic Under High‐Level Carbon Dioxide Climate Simulations

Abstract

Abstract

Abstract The tropical cyclone (TC) season, defined by the timing of storm genesis within the year, is an important but still uncertain aspect of the TC response to climate forcing, especially across different ocean basins. Here we examine changes in Northern Hemisphere TC genesis timing using statistically downscaled tropical cyclone data sets derived from large‐scale environmental fields in three idealized carbon dioxide climate states. We focus on basin‐dependent responses in the western North Pacific (WNP) and North Atlantic (NA) and evaluate the contributions of vertical wind shear (VWS), potential intensity, and the thermodynamic parameter to seasonal asymmetry. Under moderate warming, the NA season lengthens, whereas the WNP shows a modest overall contraction that reflects opposing seasonal changes in its northern and southern subregions. Seasonal‐asymmetry diagnostics show that the controls on TC seasonality are basin‐dependent under moderate warming, with VWS providing the leading contribution in most basins. In the warmest climate state, treated here as an idealized end‐member sensitivity experiment, these regional contrasts become more pronounced, with the NA becoming later and shorter and the WNP exhibiting a longer season with subregional differences. Overall, TC seasonal responses are basin‐dependent and nonmonotonic, and their dominant environmental controls differ across climate states.