Global Warming, Climate Variability and Atlantic Hurricanes

Atlantic hurricane activity is influenced by global warming and natural climate phenomena in the Pacific, Indian and Atlantic Oceans. Here we use observational data to show that global warming of the sea surface is associated with a secular increase of tropospheric vertical wind shear in the main development region (MDR) for Atlantic hurricanes. The increased wind shear coincides with a downward trend in U.S. landfalling hurricanes, a reliable measure of hurricanes over the long term. Warmings in the tropical Pacific/Indian and North Atlantic Oceans produce opposite effects upon vertical wind shear; That is, warming in the Pacific/Indian Oceans increases vertical wind shear, while warming in the North Atlantic decreases vertical wind shear. Overall, however, warming in the Pacific/Indian Oceans is of greater impact and produces increased levels of vertical wind shear which disfavors U.S. landfalling hurricanes. The relative role induced by secular warmings over the tropical oceans is key to determining whether future global warming will increase the vertical wind shear in the MDR for Atlantic hurricanes. The impact of ENSO events is that El Nino (La Nina) decreases (increases) Atlantic hurricane activity. The influence of the Atlantic multidecadal oscillation on Atlantic hurricanes is to operate through the mechanism of the atmospheric changes induced by the Atlantic warm pool (AWP). The AWP-induced changes related to Atlantic hurricanes include a dynamical parameter of vertical wind shear and a thermodynamical parameter of convective instability. A large (small) AWP reduces (enhances) the vertical wind shear in the MDR and increases (decreases) the moist static instability of the troposphere, both of which favor (disfavor) Atlantic hurricane activity.