H URRICANE IAN crashed into Florida’s coast on September 28th. It is thought to be tied as the fifth-strongest recorded hurricane to have made landfall on the contiguous United States, with winds approaching 150mph (240kph). It left Cuba in darkness after knocking out its power grid; now some 2m Floridians are without power. Two people died in Cuba; casualties in Florida are as yet unconfirmed. Just a few days earlier Typhoon Noru had slammed into the Philippines after intensifying unusually fast: it killed at least eight people and forced tens of thousands to evacuate. Are these types of storms getting worse—and is climate change to blame?
As a result of humans pumping greenhouse gases into the atmosphere, the world is on average 1.1-1.3°C hotter than it was before the Industrial Revolution. Since then there has been no increase in the number of tropical cyclones, the rapidly spinning storms known as hurricanes in the Atlantic and typhoons and cyclones elsewhere. This suggests that global warming is not making them more frequent (though it might be shifting where they occur). But the storms themselves are becoming stronger, slower, wetter and wilder.
Tropical cyclones are fuelled by the temperature of the waters across which they form and move. More than 90% of the extra heat within the climate system is sucked up by the oceans, the average surface temperatures of which are around 0.8°C above the 20th-century average. Between 1980 and 2017 the seas absorbed more than three times the amount of energy contained in the whole world’s fossil-fuel reserve. That extra power allows storms to intensify more quickly. Warmer air also holds more moisture, which both helps hurricanes last longer once they reach the coast, and increases the amount of water they can dump as rain.