Storm of Debate Over Hurricanes, Global Warming

Is global warming to blame for the last two horrific hurricane seasons?

Yes, says Judith A. Curry, a professor of atmospheric sciences at the Georgia Institute of Technology. Her argument: Worldwide sea surface temperatures have increased by about 1 degree since 1970, resulting in about 50% more tropical storm activity than normal.

No, counters James J. O’Brien, a professor of meteorology and oceanography at Florida State University. His point: Since 1850, the Earth has undergone numerous warming and cooling cycles, and there has been no distinct trend in the overall intensity of hurricane seasons.

Friday’s debate by the two climate experts at the National Hurricane Conference took on urgency in light of last season, which produced a record 28 storms, 15 of them hurricanes.

Curry said greenhouse warming, created by gases trapped in the atmosphere, had resulted in a sharp increase in tropical activity, particularly in the last decade. Since 1995, 166 tropical storms -- including 112 hurricanes, 28 of them Category 4 and 5 systems -- have been spawned in the abnormally warm waters of the Atlantic basin.

Although scientists say a natural cycle of ocean warming is responsible for that rise in activity, Curry noted that the peak period of the previous cycle, from 1945 to 1955, saw considerably fewer systems: 115 tropical storms, including 74 hurricanes, 19 of them Category 4 and 5.

As a result of global warming, hurricane seasons now are five days longer on average than they were 100 years ago, Curry said. In addition, the United States has suffered a “precipitous increase” in hurricane strikes in the last 10 years.

“We see an overall trend,” she said. “This implies some external force is raising sea surface temperatures in tropical regions.”

O’Brien, however, disputed the assertion that the world’s oceans had increased in average temperature, including in the most active tropical months, August through October. He said that to determine whether the seas had warmed, readings would have to be taken as deep as 1,000 feet worldwide.

“There’s no obvious warming,” he said.

O’Brien said that contrary to media reports, extraordinarily warm Gulf of Mexico waters did not supercharge Hurricane Katrina, which devastated New Orleans and the Gulf Coast of Mississippi in August.

Instead, he said, the normally hot water near the shoreline did.