Claims in the media that global warming is making hurricanes worse are running into a gale of their own from scientists who specialize in studying the tropical storms.
“I’m quite sure that in 15 to 20 years, everyone will look back and see what a phony issue this was,” William M. Gray, head of Colorado State University’s Tropical Meteorology Project, said. “Most of my colleagues, who have given their careers to study this, are skeptical as hell.”
Experts Dispute Claims
Nonetheless, the theory that global warming is increasing the intensity and frequency of hurricanes is drawing increasing attention, especially in the wake of Hurricane Katrina and other well-publicized storms making landfall in the U.S.
In August, for example, the media focused on a study published in the August issue of the journal Nature, which concluded the duration and strength of hurricanes have increased by about 50 percent in the past 30 years. The author of the study linked the increase to rising ocean temperatures and global warming.
Before the study’s release, Kevin Trenberth, head of the Climate Analysis Section of the National Center for Atmospheric Research, told MSNBC, “Trends in human-influenced environmental changes are now evident in hurricane regions.”
But James J. O’Brien, director of the Center for Ocean-Atmospheric Prediction Studies at Florida State University, and numerous other hurricane experts dispute the theory that global warming primes and intensifies hurricanes. These scientists say that if global warming has any effect on hurricanes, it would be small. They also attribute swings in hurricane activity to natural, 25- to 40-year cycles.
Theory ‘Demonstrably False’
O’Brien was among a group of five climatologists and other experts on climate change who wrote U.S. Sen. John McCain (R-AZ) in September 2004 a letter calling “demonstrably false” the theory that global warming was creating a surge in hurricane activity. They said the theory was based on two misconceptions: That hurricanes are increasing in intensity or frequency and that continued ocean surface warming will generate more frequent and intense storms.
In the letter to McCain, who conducted hearings on global warming in November 2004, the scientists pointed out that according to a century of National Hurricane Center reports, the decade with the largest number of hurricanes to come ashore in the United States was the 1940s, and that hurricane frequency has declined since then. They also cited data from the United Nations Environment Programme of the World Meteorological Association that hurricane frequency has declined since the 1940s.
The letter said well-documented and centuries-old evidence, as well as computer models, suggest warmer periods may actually generate a decline in the number or severity of such storms.
Atlantic Cycle Likely Cause
In an interview with Environment & Climate News, O’Brien said the more likely cause of hurricane frequency might be found in variations in the Atlantic Ocean Conveyer, the movement of the warm Gulf Stream whose waters, taken from the South Atlantic, replace the cooler, sinking water in the North Atlantic.
O’Brien said historic records show that when the conveyer is strong, there is an increase in the number and intensity of Atlantic hurricanes; when it is weak, so are the hurricane seasons. For a hurricane to grow stronger, it must keep moving over waters warmer than 80º F, which leads some people to link global warming and the storms. But, he said, there’s no scientific evidence to show that such areas of warm water are increasing in size.
Gray, too, attributes hurricane changes to cyclical fluctuations in ocean circulation, not human activity. When all the world’s oceans are taken into consideration, he said, the evidence of major changes in tropical storms is absent. One reason proponents of the global warming/hurricane link go astray is the failure to include the variable impact of ocean currents in their computer models, Gray said.
O’Brien agrees with the need for better models to describe what is a colossally complex phenomenon. But despite the complexity of understanding it, he remains confident about the outcome. “Our planet is like one big heat engine,” O’Brien said. “My view is that the planet will adjust.”
Dennis Byrne ([email protected]) is a Chicago-based writer and columnist.