Al Gore’s new movie on global warming, “An Inconvenient Truth,” opens with scenes from Hurricane Katrina slamming into New Orleans. The former vice president says unequivocally that because of global warming, it is all but certain that future hurricanes will be more violent and destructive than those in the past.
Inconvenient or not, the nation’s top hurricane scientists are divided on whether it’s the truth.
With the official start of hurricane season days away, meteorologists are unanimous that the 2006 tropical storm season, which runs from June 1 through November, is likely to be a doozy. The first tropical storm of this season showered light rain yesterday on Acapulco, a Mexican Pacific resort, but forecasters said the weather could worsen. Tropical storm Aletta was stalled 135 miles from Acapulco, with maximum winds of 45 mph, according to the U.S. National Hurricane Center in Miami, which said the storm could move toward land today.
The 2004 and 2005 Atlantic hurricane seasons broke many records, and as forecasters predict 15 named storms, nine or 10 making it to hurricane strength and four or five of those major, 2006 is shaping up as another bad one.
The top names and brightest minds in hurricane science are divided, writing papers and publishing rebuttals regarding the nature and causes of the current “active period” that began in 1995 and is expected to run at least another 10 to 15 years. They study the same facts, but draw opposite conclusions.
In one corner, subscribing to the theory that the Atlantic Basin is in a busy cycle that occurs naturally every 25 to 40 years, are Chris Landsea, science and operations officer at the National Hurricane Center in Miami, and William Gray and Phil Klotzbach of Colorado State University, who pioneered much of modern hurricane-prediction theory.
“There has been no change in the number and intensity of Category 4 or Category 5 hurricanes around the world in the last 15 years,” Mr. Landsea said, in a telephone interview from Miami.
On the other side are Kerry Emanuel of the Massachusetts Institute of Technology, one of the most respected hurricane scientists in the world, a team of meteorologists from Georgia Tech led by Peter Webster, an MIT-educated monsoon specialist, and Greg Holland, who earned his doctorate at Colorado State under Mr. Gray.
“You cannot blame any single storm or even a single season on global warming. … Gore’s statement in the movie is that we can expect more storms like Katrina in a greenhouse-warmed world. I would agree with this,” said Judith Curry. She is chairwoman of Georgia Tech’s School of Earth and Atmospheric Sciences, and is co-author, with Mr. Webster, Mr. Holland and H.R. Chang, of a paper titled “Changes in Tropical Cyclones,” in the Sept. 16 issue of Science, a weekly publication of the American Association for the Advancement of Science.
The paper concluded that there has been an 80 percent increase in Category 4 and Category 5 hurricanes worldwide.
Balancing the atmosphere
Tropical cyclones, rotating wind systems that include hurricanes, are heat engines — nature’s way of balancing extremes, mechanisms for taking heat from one place and taking it to another, as part of balancing the Earth’s atmosphere.
All agree that in the past 30 years, the waters off the West Coast of Africa, where most Atlantic hurricanes are born, have warmed by about 1 degree, to about 81 degrees Fahrenheit, and as much as two-thirds of that increase is attributable to greenhouse gases, or global warming. Where the scientists disagree is what that means for the number and intensity of hurricanes.
Mr. Emanuel of MIT said that, globally, the number and intensity of hurricanes are unchanged over the past 30 years, and that according to Japanese models, global warming could even lead to a modest decline in the number of hurricanes worldwide. However, he said that in the Atlantic Basin, where just 11 percent of all tropical storms occur, there is a “quite nice correlation” between the rise in sea surface temperature (SST) and an increase in the number and intensity of hurricanes.