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In parts of the world, tropical cyclones could become both more intense and more frequent as the planet heats up. But in the Atlantic, where these storms are called hurricanes, there might be fewer because of a weakening of a key ocean current.
鈥淵ou could argue that this is some good news, but the negative effects of climate change are devastating,鈥� says at Utrecht University in the Netherlands.
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At present, warm water from the tropical Atlantic flows north towards Greenland and northern Europe, where it cools, sinks and flows along the ocean floor back towards the southern hemisphere. This current, called the Atlantic meridional overturning circulation (AMOC), transports vast amounts of heat, shaping climates around the Atlantic.
Global warming is expected to slow down this circulation, leading to a wide range of effects, from faster sea level rise on North Atlantic coastlines to more droughts in Africa.
Standard climate models don鈥檛 have a high enough resolution to simulate tropical cyclones, so van Westen and his colleagues used a high-resolution version. They modelled a scenario in which emissions keep rising and the global temperature climbs more than 3掳C by around 2100.
According to the model, this will result in the AMOC weakening by around 25 per cent by the end of the century. Compared with the period 2003 to 2007, this is predicted to lead to a 45 per cent fall in the number of tropical cyclones in the Atlantic between 2093 and 2097, although those that form will be more intense on average.
By contrast, the model predicts that the western Pacific will see a 15 per cent increase in the number of tropical cyclones as well as an increase in intensity. The team didn鈥檛 look in detail at other parts of the world.
Van Westen presented the findings during a virtual talk at .
According to the model, there will also be a northward shift in hurricane formation in the Atlantic, with fewer tropical cyclones taking shape in the Caribbean.
The team also estimated the return times of extreme wind speeds around the Atlantic, which is a way of measuring the risk of places being hit by storms. Their findings suggest that return times will fall across most of the Caribbean and the US east coast, but rise in other areas of the North Atlantic.
If the world does eventually start reducing emissions and limits warming to well under 3掳C, van Westen expects the drop in hurricane numbers to be smaller. All his team鈥檚 findings are based on one high-resolution model, he cautions, so other groups need to do similar studies to help confirm the results.
