The destructive intensity of the winds caused by tropical storms and
hurricanes has increased significantly in the past 30 years, in line
with the theory that cyclones are becoming stronger because of global
warming, scientists said yesterday.
study of satellite data going back 25 years has found that tropical
storms in the North Atlantic and the Indian Ocean are getting
significantly stronger and therefore more likely to develop into
hurricanes with wind speeds greater than 100mph.
support the idea that the ocean acts like a "heat engine" driving
tropical cyclones. The theory is that as more heat builds up in the
oceans, the more energy there is to become converted into the strongest
winds of hurricanes.
In 1981, the average wind speed of 90 per
cent of hurricanes monitored globally by satellite came to 139 mph but,
by 2006, that speed had increased to 157mph, said Professor James
Elsner of Florida State University in Tallahassee.
"This has been
somewhat controversial but I think the evidence is fairly compelling
from our study that the strongest tropical storms and cyclones are
getting stronger. With all other things being equal, we believe the
warmer the oceans become, the bigger the maximum intensity of the
storms," he said.
"As the seas warm, the ocean has more energy
that can be converted to tropical cyclone wind. Our results do not
prove the heat-engine theory. We just show that the data is quite
consistent with it," he said.
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Tropical cyclones, which include
hurricanes, typhoons and tropical storms, occur on average about 90
times a year. The researchers analysed hurricane intensities for all
tropical cyclones occurring around the globe during the 25-year period
and looked at the maximum wind speeds recorded for each one.
idea that warmer oceans could result in stronger hurricanes was
suggested in 2005 by Kerry Emanuel of the Massachusetts Institute of
Technology, who was one of the first to find support for the theory.
Emanuel said at the time: "My results suggest that future warming may
lead to an upward trend in tropical cyclone destructive potential and -
taking into account an increasing coastal population - a substantial
increase in hurricane-related losses in the 21st century."
latest findings of Professor Elsner, published in the journal Nature,
lend powerful support to the idea. "I think there is some reason to
believe that as the oceans continue to warm, it's likely that there
will be an increase in energy that could result in an increase in
intensity of storms," he said.
However, storm intensity is not
simply the result of ocean temperatures, he added. "We still do not
have a complete understanding of why some cyclones intensify, sometimes
quite rapidly, and others don't," he said.