Experts say global warming is causing stronger hurricanes
USATODAY.com - Experts say global warming is causing stronger hurricanes: "WASHINGTON — The number of hurricanes in the most powerful categories — like Katrina and Andrew — has increased sharply over the past few decades, according to a new analysis sure to stir debate over whether global warming is worsening these deadly storms.
While studies have not found an overall increase in tropical systems worldwide, the number of storms reaching categories 4 and 5 grew from about 11 per year in the 1970s to 18 per year since 1990, according to a report in Friday's issue of the journal Science.
Peter J. Webster of the Georgia Institute of Technology said it's the warm water vapor from the oceans that drives tropical storms, and as the water gets warmer the amount of evaporation increases, providing more fuel for the tempests. Between 1970 and 2004 the average sea surface temperature in the tropics rose nearly 1°F.
Co-author Greg Holland of the National Center for Atmospheric Research said the researchers can't say rising sea-surface temperatures caused Hurricane Katrina. But their study shows the potential for more Katrina-like events to occur, he said.
Katrina was a category 5 storm at sea and was category 4 when it made landfall. The increase in storms they found is for category 4 and 5. Category 4 storms have wind speeds of 131 mph to 155 mph and Category 5 is for storms with sustained winds of 156 mph and over. (Related graphic:Saffir-Simpson scale of hurricane intensity.)"
 | Katrina was a Category 5 hurricane while in the Gulf of Mexico, but made landfall as a Category 4. NOAA |
While studies have not found an overall increase in tropical systems worldwide, the number of storms reaching categories 4 and 5 grew from about 11 per year in the 1970s to 18 per year since 1990, according to a report in Friday's issue of the journal Science.
Peter J. Webster of the Georgia Institute of Technology said it's the warm water vapor from the oceans that drives tropical storms, and as the water gets warmer the amount of evaporation increases, providing more fuel for the tempests. Between 1970 and 2004 the average sea surface temperature in the tropics rose nearly 1°F.
Co-author Greg Holland of the National Center for Atmospheric Research said the researchers can't say rising sea-surface temperatures caused Hurricane Katrina. But their study shows the potential for more Katrina-like events to occur, he said.
Katrina was a category 5 storm at sea and was category 4 when it made landfall. The increase in storms they found is for category 4 and 5. Category 4 storms have wind speeds of 131 mph to 155 mph and Category 5 is for storms with sustained winds of 156 mph and over. (Related graphic:Saffir-Simpson scale of hurricane intensity.)"
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