Recent Results on Hurricanes and Climate
Suzana J. Camargo
Lamont-Doherty Earth Observatory
Columbia University

In this talk I will discuss recent results from 2 different studies on hurricanes and climate. In the first one, we analyzed tropical cyclone genesis indices (TCGIs), which are functions of the large-scale environment that are designed to be proxies for the probability of tropical cyclone (TC) genesis. While the performance of TCGIs in the current climate can be assessed by direct comparison to TC observations, their ability to represent future TC activity based on projections of the large-scale environment cannot. We examined the performance of TCGIs in high-resolution atmospheric model simulations forced with sea surface temperatures (SST) of future, warmer climate scenarios, using a perfect model framework. We investigated whether the TCGIs derived for the present climate can, when computed from large-scale fields taken from future climate simulations, capture the simulated global mean decreases in TC frequency projected by this model. The TCGIs differ in their choice of environmental predictors, and several choices of predictors perform well in the present climate. However, some TCGIs that perform well in the present climate do not accurately reproduce the simulated future decrease in TC frequency.

In a second study, the impact of the Montreal Protocol on the potential intensity of tropical cyclones over the next 50 years is investigated with the Whole Atmosphere Community Climate Model (WACCM), a state-of-the-art, stratosphere-resolving atmospheric model, coupled to land, ocean, and sea-ice components, and with interactive stratospheric chemistry. An ensemble of WACCM runs from 2006 to 2065 forced with a standard future scenario is compared to a second ensemble in which ozone depleting substances are not regulated (the so-called `World Avoided'). It is found that by the year 2065, changes in the potential intensity of tropical cyclones in the World Avoided are nearly three times as large as for standard scenario. The Montreal Protocol thus provides a strong mitigation of the adverse effects of intensifying tropical cyclones. The relative importance of warmer sea surface temperatures (ozone depleting substances are important greenhouse gases) and cooler lower stratospheric temperatures (accompanying the massive destruction on the ozone layer) are carefully examined.