Changes in Tropical Cyclone Activity due to Global Warming in a General Circulation Model

This study investigates the possible changes that the greenhouse global warming might generate in
the characteristics of the tropical cyclones (TCs). The analysis has been performed using scenario
climate simulations carried out with a fully coupled high-resolution global general circulation
model. 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 observations.
The model appears to be able to simulate tropical cyclone-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 frequency
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 amount of convective
instabilities. 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 is evidence of increased rainfall associated with the simulated cyclones. 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 20° latitude in both Hemispheres.
An extended version of this work is in available on Journal of Climate (Gualdi et al.,2008 - DOI:10.1175/2008JCLI1921.1)