Climate change has driven a 13% decline in the frequency of tropical cyclones since pre-industrial times, new research finds.
Tropical cyclones are complex phenomena, which only form under specific atmospheric and oceanic conditions. Research suggests that, as the climate warms, changing conditions are making tropical cyclones less frequent. However, a lack of long-term cyclone data makes this trend difficult to quantify.
The paper, published in Nature Climate Change, aims to fill this gap using “reanalysis” data that combines observations and model simulations. The findings show a 13% decrease in tropical cyclones around the world between 1850-1900 and 1900-2000. More specifically, they find a drop from more than 100 tropical cyclones a year in pre-industrial times to around 80 in 2012. The study does not look at changes in the intensity – or damage – of cyclones over this period.
Warming is causing two major global atmospheric circulations – the Walker and Hadley circulations – to weaken, with knock-on effects that create “more hostile conditions” for cyclones to form, the authors suggest.
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While cyclone frequency has declined over 1900-2012 in six of the seven regions the study investigates, the researchers find a slight increase in the North Atlantic, driven by a rising trend over recent decades. They suggest that this is due to a combination of natural variability and a decrease in local air pollution.
This is a ”very interesting and important paper”, a scientist not involved in the study tells Carbon Brief. He adds that it is “the first paper to demonstrate that anthropogenic global warming has already produced a significant drop in the numbers of tropical systems both globally and the Atlantic between pre-industrial conditions and during the 20th century”.
The decrease in tropical cyclone frequency is “good news”, the lead author of the study tells Carbon Brief. However, he adds that it is not the whole story – emphasising that through changes in cyclone intensity and location, climate change has already put many people at greater risk from tropical cyclones.
The authors also investigate the difference between tropical cyclone occurrence in northern and southern hemispheres. They find that the most tropical cyclones occur in the northern hemisphere, but that the decline in tropical cyclones frequency was more significant here. Between the pre-industrial period and 2012, the number of tropical cyclones recorded in the northern hemisphere per year dropped from approximately 75 to 60.
