Climate change could be reducing the likelihood of tropical cyclones
appears to be reducing the likelihood of tropical cyclones across the world, researchers suggest. They found that the annual number of such storms decreased by about 13 per cent during the 20th century, compared with the period between 1850 and 1900. For most tropical cyclone basins, this decline has accelerated since the 1950s, which the authors of the new study suggest is mainly because of a weakening of tropical atmospheric circulation. It supports the theory that climate change leads to a decrease in the number of tropical cyclones, they said. However, the University of Melbourne-led experts warned that frequency is just one factor in the dangers tropical cyclones pose. They did not study changes in intensity or location. The researchers said it was also not clear how cyclones change under human emissions because a warming ocean is expected to intensify storms, while some changes in atmospheric circulation are thought to prevent storm formation. As their name suggests, tropical cyclones have long been characterised by the fact that they form almost exclusively over seas located at low-latitudes. Key to these storms are warm sea surface temperatures of at least 81F (27C) and converging low-level winds that force air to rise and form storm clouds. As long as the burgeoning system has enough distance from the equator, planetary spin will interact with the flow of moist rising air, causing it to rotate cyclonically. And just as cyclones do not form too close to the equator, their range is bounded at higher latitudes by the jet streams, which have long confined them to the tropics. Providing historical context to the frequency of cyclones is challenging because the observational record is not complete, especially before 1950, so the experts used a combination of past records and modelling. .