"As far as I can tell, there is no dispute that higher sea temperatures mean more energy for these storms to feed on," said Kevin Trenberth of the
Trenberth is convinced that global warming is a major factor in spawning the kinds of intense hurricanes that kill, and he is hardly alone.
The U.N. Intergovernmental Panel on Climate Change, which set out the consequences of global warming in a series of reports this year, said future hurricanes and typhoons will probably be more intense as tropical seas continue to heat up.
However, Chris Landsea of the
HOW MUCH IMPACT FROM GLOBAL WARMING?
When it comes to the relationship between hurricane strength and global warming, "the important question is not, is there an impact, but how much of an impact," Landsea said in a telephone interview. "When you look at all of the studies ... it's a pretty tiny sensitivity.
Sea surface temperatures have risen an average of about that much in the tropical Atlantic, the Caribbean and the
He said that 1 percent difference in intensity, gauged by the force of the storm winds, makes little difference, even in a storm with the devastating strength of 2005's Katrina, a top-ranked Category 5 hurricane. "Consider that we can only estimate winds to the nearest 5 miles (8 km) an hour here at the hurricane center and when you get to Category 4 or 5, you're really making a guess to the nearest 10 miles (16 km) an hour," Landsea said. "A 1- or 2-mile an hour (1.6 to 3.2 km) change is so tiny you can't even measure it."
But Trenberth noted that global climate change was a big factor in driving the spike in sea surface warming in 2005, a hurricane season that broke records for its intensity.
Tropical sea temperatures were up by 1.6 degrees F (.92 degree C) in 2005. "That's way higher than the next highest on record for the period," Trenberth said. Global warming accounted for about half of that rise, he said.
By contrast, the
'GLOBAL WARMING DOESN'T GO AWAY'
"The key thing about global warming is it doesn't go away," Trenberth said. "It provides a background level (of warming), and the natural fluctuations can be thought of as occurring on top of it."
Kerry Emanuel, a climate scientist at the Massachusetts Institute of Technology, stated plainly that human-caused global warming contributes to hurricane intensity. There has been a large upswing in the frequency of Atlantic hurricanes, beginning in 1995," Emanuel said on his Web site, http://wind.mit.edu/~emanuel/anthro2.htm. "This corresponds to an upswing in tropical
Emanuel said there was no evidence that natural cycles or regional Atlantic climate phenomena are affecting sea surface temperatures, which have an impact on hurricanes.
John Holdren, a climate scientist at
The matter is not settled. A study published in Nature last week said hurricanes over the past 5,000 years appear to have been controlled more by El Nino and an African monsoon than warm local sea surface temperatures.