September 1, 2005
Katrina Reignites Global Warming Debate
Hurricane Katrina's fury has reignited the scientific debate over whether global warming might be making hurricanes more ferocious.
At least one prominent study suggests that hurricanes have become significantly stronger in the past few decades during the same period that global average temperatures have increased.
Katrina blew up in the Gulf of Mexico to a Category 5 hurricane with winds of 175 mph before slackening a bit Monday when it hit, swamping New Orleans and the Mississippi coast.
Other leading scientists agree the Atlantic Basin and Gulf Coast regions are being battered by a severe hurricane phase that could persist for another 20 years or more. But they believe that a natural environmental cycle is responsible rather than any human-induced change, and they point to what they consider to be large gaps in the global warming analysis conducted by a climatologist at the Massachusetts Institute of Technology.
Roger Pielke Jr., who studies the social impacts of natural disasters and climate change at the University of Colorado, said any link between the intensity of Katrina and other recent hurricanes and global warming is "premature." Most forecasts suggest climate change would increase hurricane wind speeds by 5 percent or less later in this century.
Pielke's analysis will be published later this year in the Bulletin of the American Meteorological Society.
"There are good reasons to expect that any conclusive connection between global warming and hurricanes or their impacts will not be made in the near term," he said.
In August, MIT climatologist Kerry Emanuel reported in the journal Nature that major storms spinning in both the Atlantic and the Pacific have increased in duration and intensity by about 50 percent since the 1970s.
During that period, global average temperatures have risen by about one degree Fahrenheit along with increases in the level of carbon dioxide and other heat-trapping pollutants from industry smokestacks, traffic exhaust and other sources.
Hurricanes rely on huge pools of warm water at the surface of the ocean to grow for several days. As trade winds spin the storm, it pulls more heat from the ocean and uses it as fuel. Typically, large storms require sea surface temperatures of at least 81 F.
Scientists say rising global atmospheric temperatures have been slowly raising ocean temperatures, although they still vary widely from year to year.
On Web logs, scientists and environmentalists in the United States and Europe sparred over the possible connection.
The evidence linking global warming and hurricane intensity might be fuzzy, but it highlights a potential issue worth examining right away, some say.
"Maybe a connection here is yet to be clearly established, but it is also yet to be ruled out," said Terry Richardson, a physicist at the College of Charleston in South Carolina on CCNet, a British climate blog.
Pielke and other researchers, including meteorologists at federal weather laboratories, say Emanuel's evidence is too slim at this point.
The past 10 years have been the most active hurricane seasons on record, and many researchers say the trend could persist for another 20 years or more. They believe it's a consequence of natural salinity and temperature change in the Atlantic's deep current circulation - elements that shift back and forth every 40-60 years.