Global Warming

Study: Global warming pushing hurricanes out of tropics

Tropical cyclones worldwide are moving out of the tropics and more toward the poles and generally larger populations, likely because of global warming, a surprising 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.

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

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 a decade, which just could be random.

The scientists say the changes start with man-made global warming, which alters air circulation from the tropics to just 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 favourable for storm intensification.