Is climate change making hurricanes worse?
HURRICANE IAN crashed into Floridas 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 worseand is climate change to blame? As a result of humans pumping greenhouse gases into the atmosphere, the world is on average 1.1-1.3C 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 0.8C above the 20th-century average. Between 1980 and 2017 the seas absorbed more than three times the amount of energy contained in the whole worlds 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. Climate change also appears to be influencing the paths hurricanes take across land. The speed and direction of storms are steered by airflows in various parts of the atmosphere, which seem to be growing more sluggish as global temperatures rise (though it is not yet clear why). That makes it more likely that hurricanes move slowly or hover over one location, increasing their capacity for destruction. A study by Americas weather and space agencies found that the average forward speed of North Atlantic hurricanes decreased by 17% between 1944 and 2017. In August 2017 Hurricane Harvey stalled for three days over Houston, Texas, where it released record amounts of rainfall, causing catastrophic flooding. Scientists subsequently determined that the event had been made three times more likely by climate change. Climate change is also causing sea levels to rise, as ice caps and glaciers melt and because water expands as it warms. This increases another threat posed by hurricanes, which thrust seawater towards the shore as they move in. Higher seas mean that surges travel farther inland, reaching more people and buildings. Differences in gravity and currents mean that the extra water in the oceans is not equally distributed across all coastlines. Around Fort Myers, a Floridian city in Ians path, sea levels are 33.7cm higher today than they were a century ago. The storm surge there was up to 3.7 metres, submerging cars and homes. All these factors combine to make hurricanes more damaging to property and livelihoods. (Deaths, though, are decreasing, as forecasting and emergency response times improve). The total cost of weather and climate disasters in Americato which storms are the largest contributorin the past five years was $788bn, about one-third of the total for 1980-2022 (adjusting for inflation). But climate change is not entirely to blame. So too is the propensity to build on vulnerable stretches of coastline. Between 2010 and 2020 Floridas population grew by nearly 15%, double Americas national rate. People have also flocked to the Atlantic coast. Ultimately, mankind is to blame twice over: for changing the climate to make hurricanes more dangerous, and for continuing to put itself in their path. More from The Economist explains: How revolutionary is Californias ban on petrol-powered cars? Why forests need wildfires Why monsoon season will not solve Indias water crisis