Response of Tropical Cyclone Potential Intensity to a Global Warming Scenario in the IPCC AR4 CGCMs

This paper reports on an analysis of the tropical cyclone (TC) potential intensity (PI) and its control parameters in transient global warming simulations. Specifically the TC PI is calculated for Coupled Model Intercomparison Project/CMIP3 integrations during the first 70 years of a transient run forced by 1% per year CO2 increase. The linear trend over the period is used to project a 70-yr change in relevant model parameters. The results for a 15-model ensemble mean climate projection show that the thermodynamic potential intensity (THPI) increases on average by 1.0%~3.1% over various TC basins, which is mainly attributed to changes in the disequilibrium in enthalpy between the ocean and atmosphere, in the transient response to increasing CO2 concentrations. This modest projected increase in THPI is consistent with that found in other recent studies.

In this paper we also quantify the effects of evolving large-scale dynamical factors on the projected TC PI using the empirical formulation of Zeng et al. (2007, 2008), which takes into account the effects of vertical shear and translational speed based on a statistical analysis of present day observations. Including the dynamical efficiency in the formulation of PI leads to larger projected changes in PI relative to that obtained using just THPI in some basins and smaller projected changes in others. The inclusion of the dynamical efficiency has the largest relative effect in the main development region (MDR) of the North Atlantic where it leads to a 50% reduction in the projected PI change. Results are also presented for the basin-average changes in PI for the climate projections from each of the 15 individual models. There is considerable variation among the results for individual model projections, and for some models the projected increase in PI in the Eastern Pacific and South Indian Ocean regions exceeds 10%.