Hurricanes whip up faster in warming world, says new study
By Becky Oskin
7 September 2012 (LiveScience) – Global warming may fuel stronger hurricanes whose winds whip up faster, new research suggests. Hurricanes and other tropical cyclones across the globe reach Category 3 wind speeds nearly nine hours earlier than they did 25 years ago, the study found. In the North Atlantic, the storms have shaved almost a day (20 hours) off their spin-up to Category 3, the researchers report. (Category 3 hurricanes have winds between 111 and 129 mph, or 178 and 208 kph.) “Storms are intensifying at a much more rapid pace than they used to 25 years back,” said climatologist Dev Niyogi, a professor at Purdue University in Indiana and senior author of the study. The work helps support the theory that rising ocean temperatures have shifted the intensity of tropical cyclones, which include hurricanes and typhoons, to higher levels. In the past century, sea surface temperatures have risen 0.9 degree Fahrenheit (0.5 degree Celsius) globally. Scientists continue to debate whether this increase in temperature will boost the intensity or the number of storms, or both. Globally, about 90 tropical cyclones, on average, occur every year. Tropical cyclones form when warm, moist air over the ocean surface fuels convection. The storms act like heat engines: The warmer the ocean surface, the more energy there is to power a storm’s fierce winds. As such, scientists have hypothesized global warming and the associated rising heat of sea surfaces would fuel intense hurricanes. Most of the initial strengthening of storms, from Category 1 to Category 3, happens on the open ocean, not as a storm is approaching land. So even if storms are intensifying more quickly, it may not result in higher peak wind speeds and more rainfall when hurricanes make landfall. (Category 1 storms have wind speeds of at least 74 mph, or 119 kph.) [5 Hurricane Categories: Historical Examples] But Niyogi and his colleagues found an overall shift toward more intense storms in all ocean basins except the East Pacific. “They are getting stronger more quickly, and also higher category. The intensity as well as the rate of intensity is increasing,” said Niyogi. And that makes it a simple numbers game – with more strong storms forming in the oceans, the chance of having powerful hurricanes hit the coast rises. “If storms in general are intensifying faster, then these storms making landfall could have a greater probability of being stronger storms,” Niyogi told LiveScience. The researchers also report that storms in the North Atlantic now typically mature from a Category 1 to a Category 3 in 40 hours instead of the 60 hours that transition took 25 years ago. (Hurricane Michael, currently swirling far out over the Atlantic went from a Category 1 hurricane to a Category 3 in about 6 hours, according to reports from the National Hurricane Center.) The North Atlantic basin also shows the strongest warming trends during the study period. In the past 30 years, sea surface temperatures in Hurricane Alley – the main Atlantic hurricane development region – increased nearly 2 degrees Fahrenheit (1 degree Celsius). The research is detailed in the 26 May 2012 issue of the journal Geophysical Research Letters. […] But the risk of damage from stronger storms is outweighed by the expected financial hit from people putting themselves in harm’s way, according to a study published in the 28 August 2012 issue of Geophysical Research Letters. […]
