WASHINGTON – Typhoons, cyclones and hurricanes worldwide are shifting out of the tropics and more toward the poles and generally larger populations, likely because of global warming, a new study finds. Atlantic hurricanes, however, don’t follow this trend.
While other studies have looked at the storms’ strength and frequency, this is the first study that looks at where they are geographically when they peak.
It found that in the last 30 years, they are peaking 33 miles (53 kilometers) farther north each decade in the Northern Hemisphere and 38 miles (61 kilometers) farther south each decade in the Southern Hemisphere.
That means the storms have moved about 100 miles (160 kilometers) toward the more populous mid-latitudes since 1982, the starting date of the study released Wednesday by the science journal Nature.
Known as typhoons in Japan, the storms are called hurricanes in North America and cyclones elsewhere — they are essentially the same weather pattern.
“The storms en masse are migrating out of the tropics,” said study lead author James Kossin of the National Climatic Data Center and the University of Wisconsin.
Kossin used historical tracks of storms in the Western Pacific, Eastern Pacific, North Indian Ocean, South Indian Ocean, South Pacific and the Atlantic.
That means more people at risk, especially in the Northern Hemisphere, because “you’re going to hit more population areas,” said Yale University historian and cartographer Bill Rankin, who wasn’t part of the study.
In the region where Japan tracks typhoons, they are peaking 68 kilometers (42 miles) farther north each decade.
That means cyclones that used to hit their strongest around the same latitude as the northern Philippines are now peaking closer to Hong Kong, Taiwan, Shanghai, Japan and South Korea, Kossin said. About 60 million people live in Taiwan, Hong Kong, Shanghai and Tokyo alone.
The trend, however, is not statistically significant in the Atlantic basin, where storms threaten the U.S. East Coast. In the Atlantic region, the study has seen a northward drift of storms of only 4 miles (6 kilometers) a decade, which just could be random.
Kossin said the Atlantic region is different because of changes in pollution over the U.S. and other factors.
Kossin and colleagues say the changes start with man-made global warming, which alters air circulation from the tropics to farther north and south.
In the tropics, those changes increase upper atmosphere wind shifts called shear that weaken cyclone development. At higher latitudes, the changes decrease the storm-decapitating shear, making those areas more favorable for storm intensification.
“The tropics are becoming less hospitable” for these storms, Kossin said. “The higher latitudes are becoming less hostile.”
Past storm studies have been criticized because data don’t go back many years. But Kossin, his colleagues and outside scientists say that by looking at where geographically storms hit their peak, this study avoids problems with haphazard measurements and thus can make a stronger connection to climate change.
“This is an important, very well-researched paper that uncovers something that was unknown previously,” said hurricane researcher Chris Landsea, science officer at the National Hurricane Center. Florida International University hurricane professor Hugh Willoughby called this the strongest link yet between man-made global warming and tropical cyclones.