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Study: Tropical cyclones migrating out of tropics

WASHINGTON — Tropical cyclones worldwide are moving 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 strength and frequency of the storms, which are called hurricanes in North America, this is the first study that looks at where they are geographically when they peak. It found in the last 30 years, tropical cyclones, regardless of their size, are peaking 33 miles farther north each decade in the Northern Hemisphere and 38 miles farther south each decade in the Southern Hemisphere.

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That means about 100 miles toward the more populous midlatitudes since 1982, the starting date for the study released Wednesday by the journal Nature.

‘‘The storms en masse are migrating out of the tropics,’’ said James Kossin, the study’s lead author. Kossin, of the National Climatic Data Center and the University of Wisconsin, 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 are 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 cyclones, they are peaking 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.

Kossin said the Atlantic region is different because of changes in pollution over the United States and other factors.

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