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Changes in Tropical Cyclone Activity Due to Global Warming: Results from a High-Resolution Coupled General Circulation Model

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Document pages: 41 pages

Abstract: This study investigates the possible changes that the greenhouse global warming might generate in the characteristics of the tropical cyclones (TCs). To this aim, scenario climate simulations, performed with a fully coupled high-resolution global general circulation model, have been analyzed. First of all the capability of the model to reproduce a reasonably realistic TC climatology has been assessed by comparing the model results from a simulation of the 20th Century with observational data sets. Then, the changes in the model TCs induced by atmospheric CO2 increase have been quantified. From the current climate simulation, the model appears to be able to simulate tropical cyclon-like vortices with many features similar to the observed TCs. The simulated TC activity exhibits realistic geographical distribution, seasonal modulation and interannual variability, suggesting that the model is able to reproduce the major basic mechanisms that link the TC occurrence with the large scale circulation. The results from the climate scenarios reveal a substantial general reduction of the TC activity when the atmospheric CO2 concentration is doubled and quadrupled. The reduction appears particularly evident for the tropical north west Pacific (NWP) and north Atlantic (ATL). In the NWP the weaker TC activity seems to be associated with a reduced efficiency of triggering of convective instabilities due to a rise of the level of free convection. In the ATL region the weaker TC activity seems to be due to both the increased stability of the atmosphere and a stronger vertical wind shear. Despite the generally reduced TC activity, there are evidences of increased intensity of the simulated cyclones in terms of rainfall. Despite the overall warming of the tropical upper ocean and the expansion of warm SSTs to the subtropics and mid-latitudes, the action of the TCS remains well confined to the tropical region and the peak of TC number remains equatorward of 20o latitude in both the Hemispheres.

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