Global warming is affecting the intensity of Atlantic hurricanes, according to a new study by a university professor in Florida who says his research provides the first direct link between climate change and storm strength.
James Elsner of Florida State University said he set out to perform a statistical analysis of the two theories in a raging debate within the scientific community: Whether recent intense hurricanes are the result of climate change or natural ocean warming and cooling cycles.
"Is the atmosphere forcing the ocean or the ocean forcing the atmosphere?" Elsner asked.
The issue has a wide-ranging impact on insurance companies, municipal planners, some 50 million residents of hurricane-prone US coastal communities and millions of others in Mexico, Central America and the Caribbean islands.
The 2005 hurricane season produced 28 tropical storms and hurricanes, shattering the old record of 21 set in 1933.
Four of the hurricanes were Category 5, the strongest on the five-step Saffir-Simpson scale. One of those, Wilma, was the most intense Atlantic hurricane ever recorded.
The season also produced Katrina, which killed more than 1,300 people and caused about $80 billion in damage when it swamped New Orleans and other parts of the US Gulf coast.
Elsner looked at 135 years of records to examine the statistical connection between Atlantic sea surface temperatures and air temperatures near the sea surface, and then compared them to records of hurricane intensities.
Atlantic hurricanes draw their energy from the warm waters of the Atlantic Ocean, Gulf of Mexico and Caribbean Sea.
He found that average air temperatures during hurricane season between June and November were useful in predicting sea surface temperatures, but not the other way around.
"It appears that atmospheric warming comes before sea warming," he said, indicating that hurricane damage will be likely to continue increasing because of greenhouse warming.
The study was scheduled to be published August 23 in Geophysical Research Letters, a journal of the American Geophysical Union.
Many hurricane researchers say the Atlantic basin moved into a period of increased hurricane activity about a decade ago and predicted it could last 25 to 40 years.
Some say it is due to a natural fluctuation in sea surface temperatures called the Atlantic Multidecadal Oscillation.
But a growing body of research indicates human-induced global warming -- driven by heat-trapping gases in air pollution from cars and factories -- could be heating sea water, which in turn fuels stronger hurricanes.
Elsner described himself as "sympathetic" to the idea of human-induced global warming but said his research merely tried to determine whether there was a link between climate change and intense hurricanes.
"I think there are ocean currents that warm and cool the oceans," he said. "But it's not clear that kind of change is a multidecadal change and I'm not clear that there is a strong natural variability in the Atlantic."