Changes in tropical cyclone activity are among the more potentially consequential results of global climate change, and it is therefore of considerable interest to understand how anthropogenic climate change may affect such storms. Global climate models are currently used to estimate future climate change, but the current generation of models lacks the horizontal resolution necessary to resolve the intense inner core of tropical cyclones. Here we review a new technique for inferring tropical cyclone climatology from the output of global models, extend it to predict genesis climatologies (rather than relying on historical climatology), and apply it to current and future climate states simulated by a suite of global models developed in support of the most recent IPCC report. This new technique solves the horizontal resolution problem by using a specialized, coupled ocean-atmosphere hurricane model phrased in angular momentum coordinates, which provide high resolution of the core at low cost. This model is run along each of two thousand storm tracks generated using an advection-and-beta model, which is in turn driven by large-scale winds derived from the global models. In an extension to this method, tracks are initiated by randomly seeding large areas of the tropics with weak vortices and then allowing the intensity model to determine their survival, based on large-scale environmental conditions. We show that this method is largely successful in reproducing the observed spatial distribution, seasonal cycle, and interannual variability of tropical cyclones in the present climate. When applied to simulations of global climate with double the present concentration of carbon dioxide, this method predicts substantial changes and geographic shifts in tropical cyclone activity, but with much variation among the global climate models used. Changes in basin-wide power dissipation vary greatly from model to model and from basin to basin, but in general, storm frequency decreases and the frequency of landfall events declines nearly everywhere. We demonstrate that in these simulations, the decrease in tropical cyclone activity is caused by the increasing difference between the moist entropy of the boundary layer and that of the middle troposphere as the climate warms.

Full Article: ftp://texmex.mit.edu/pub/emanuel/PAPERS/Emanuel_etal_2008.pdf

Last Updated: 2008-08-21