Tropical cyclones really are growing stronger as the world warms

trains in floodwater

Typhoon Hagibis hit Japan in October 2019

Richard Atrero de Guzman/ Sipa USA

Tropical cyclones around the world have grown stronger since the 1970s, just as theory and models predicted.

“The signal has now risen above the noise,” says James Kossin of the US National Oceanic and Atmospheric Administration. “This is the first time we have been able to find a global trend in the existing data.”

Hurricanes and typhoons, as tropical cyclones are called in different parts of the world, are fuelled by warm surface waters. There is more fuel in a warmer world, which led to the idea that storms would grow stronger.

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But the low and variable number of tropical cyclones each year has made it hard to tell if there is a statistically significant trend. What’s more, there have been dramatic improvements in observations, which makes it hard to tell if any trend is genuine.

To compensate, Kossin’s team looked only at data from geostationary satellites, which began observing in 1979. The researchers then downgraded the quality of more recent satellite data to match the quality of early records.

They found a clear trend, with the probability of a hurricane having wind speeds of at least 185 kilometres per hour increasing by 15 per cent.

This study didn’t look at what caused this trend, but when put together with all the other evidence a clear picture emerges. “It’s highly likely that there’s a human fingerprint on this,” says Kossin.

Other studies suggest that global warming is making tropical cyclones more dangerous in other ways, too. They may be intensifying faster, meaning there is less time to warn of impending danger. They may also be producing more rainfall and moving more slowly, meaning more rain falls in one place. Rising sea levels are also making storm surges higher.

There also seems to be a poleward shift in the stronger storms, says Kossin. This would be good news for some countries such as the Philippines, but bad news for others such as Japan.

Journal reference: PNAS, DOI: 10.1073/pnas.1920849117

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