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13 April, 2021, Berlin: Sea surface temperature rise driven by climate change has doubled the chances of extremely active Atlantic tropical cyclone seasons according to a new peer-reviewed study from research organisation Climate Analytics.

The study, published today in Weather and Climate Dynamics, looks at data from 1982 to 2020, finding that an extremely active Atlantic tropical cyclone season – classified by the US National Oceanic and Atmospheric Administration (NOAA) as a season with an accumulated cyclone energy above 160 – was made 200% more likely in 2020 by man-made ocean warming.

“While the attribution of individual tropical cyclone events remains difficult, there can be no doubt that climate change is creating more intense storms,” commented lead author, Peter Pfleiderer.

“Our results do not imply that increasing sea-surface temperatures lead to more tropical cyclones – but point towards a trend of more intense storms and therefore more extreme outcomes for seasons with many tropical cyclones,” he added.

Is it climate change?

The formation of tropical cyclones and their intensity primarily depends on ‘seasonal atmospheric circulation’ – the year-to-year differences in wind patterns at different levels of the atmosphere. The attribution of tropical cyclone events to climate change remains challenging due to the difficulty of simulating tropical cyclones in climate models and the strong year-to-year variability in atmospheric circulation.

To overcome this, the researchers instead looked at the increase in sea surface temperatures, which are well understood, and can robustly be attributed to human-influenced climate change.

“This study looks at the changes stemming from increasing sea surface temperatures, but it has to be expected that atmospheric circulation changes from global warming also affects tropical cyclone activity – so our results could be conservative,” Pfleiderer added.

Disaster, year after year

Tropical cyclones are among the most damaging extreme weather events and can devastate vulnerable countries. Separate research from 2019 showed that in the past 20 years, some Caribbean Small Island Developing States have been hit by a major hurricane (an intense tropical cyclone that reaches category four or five) eight times. GDP losses from tropical cyclones average at 3.7% per year, with the most affected Caribbean country, Dominica, averaging yearly losses of 21.2%.

This year’s Atlantic tropical cyclone season starts in August and forecasts published this week by the same group of researchers predict that it will be extremely active – with an estimated accumulated cyclone energy of 164. This would be the third extremely active season in the last decade.

For comparison, the 2017 season – which was the costliest on record, with major Hurricanes Harvey, Irma and Maria – had an ACE of roughly 225. In Barbuda over 90% of structures were destroyed, resulting in the island being completely uninhabited for the first time in 300 years.