Global warming has been blamed for much, and one recent study shows higher worldwide temperatures is pushing tropical cyclones out of the tropics toward the poles – and that means greater catastrophic risk for Canadian insurers.
“The storms en masse are migrating out of the tropics,” says 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.
An Environment Canada survey team investigated wind damage from severe thunderstorms that roared across the Mildmay area southwest of Owen Sound on Tuesday afternoon.
The team confirmed that wind damage was likely caused by a low end tornado with estimated wind speeds near 150 km/h.
The tornado caused a west to east damage path about two kilometres long and up to 150 metres wide close to Mildmay. One house suffered significant damage, while two barns were also damaged, along with trees and hydro poles.
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 53 kilometres farther north each decade in the Northern Hemisphere and 61 kilometres farther south each decade in the Southern Hemisphere.
Atlantic hurricanes, however, don't follow this trend. (continued.)
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That means about 160 kilometres toward the more populous mid-latitudes since 1982, the starting date for the study released yesterday by the journal Nature.
That means more people at risk, especially in the Northern Hemisphere, because “you're going to hit more population areas,” says Yale University historian and cartographer Bill Rankin, who wasn't part of the study.
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 6.4 kilometres a decade, which just could be random.
Kossin said the Atlantic region is different because of changes in pollution over the United States and other factors.
Kossin and colleagues 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.
“The tropics are becoming less hospitable” for these storms, says Kossin. “The higher latitudes are becoming less hostile.”
Past storm studies have been criticized because data doesn't go back many years. But Kossin, his colleagues and outside scientists say 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,” says hurricane researcher Chris Landsea, science officer at the National Hurricane Center.
Florida International University hurricane professor Hugh Willoughby called this the strongest tropical cyclone and global warming link yet.
