Implications of anthropogenic climate change for tropical cyclone activity: A case study with the NCAR CCM2

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. The changes associated with global warming were examined in terms of the frequency of occurrence, and mean intensity of TCs. The frequency of global TC occurrence remains unchanged in response to the CO2-induced warming. Although the hydrologic cycle is generally enhanced in the warmed climate, increased precipitation does not necessarily make a great impact on TC activity. This unchanged global TC frequency seems to coincide with almost neutral variations in the zonally-averaged moist instability in the tropics. However, there is some uncertainty in the model regarding the treatment of physical processes that control moisture distributions in the middle to lower troposphere. On the regional scale, the CO2-induced changes in TC occurrence were generally not statistically significant. TC intensities were enhanced over warmed SST regions in the western Pacific, which contribute to the significantly increased mean intensity of global TCs.