CLIMATOLOGICAL CHANGES IN TROPICAL CYCLONES ASSOCIATED WITH GLOBAL WARMING

A NUMERICAL EXPERIMENT WITH AN ATMOSPHERIC GENERAL CIRCULATION MODEL

Abstract

To investigate the impacts of anthropogenic global warming on tropical cyclone (TC) activity, climate simulations were conducted under the present and CO₂-warmed conditions using the National Center for Atmospheric Research Community Climate Model version 2. The CO₂-warmed condition includes doubled atmospheric CO₂ concentration and about 1°C of tropical sea surface temperature (SST) warming. Simulated TCs were objectively selected from twice daily instantaneous outputs during an eight-year time integration period of each simulation, and the changes associated with global warming were examined in terms of frequency of occurrence and mean intensity.
The frequency of global TC occurrence remains unchanged in response to the CO₂-induced warming. This fairly constant global TC frequency is in agreement with the almost neutral tendency in the zonally-averaged moist instability in the tropics. On the other hand, regional TC frequencies indicate relatively large tendencies depending on TC basins, including increased tendency in the western North Pacific and decreased tendency in the Western Hemisphere. These regional variations are connected with large-scale circulation and similar to the natural variability of observed TCs. Simulated changes in the mean TC intensity highlight increased tendencies over the warm SST regions in the western Pacific, which contribute to the significantly increased mean intensity of global TCs.