Global Warming to Decrease Hurricanes, Study Says

Willie Drye
for National Geographic News
May 19, 2008
Global warming may reduce the number of hurricanes forming in the Atlantic Basin by 2060, a new study says. But it adds that the storms that do form may be slightly stronger and wetter.

The study, conducted by scientists at the U.S. National Oceanic and Atmospheric Administration (NOAA), is the latest development in a contentious debate about whether global warming is influencing hurricanes.

The new research suggests that the number of hurricanes each summer could decrease by about 18 percent.

Major hurricanes—those with winds in excess of 110 miles (177 kilometers) an hour—could decline by about 8 percent.

Currently about ten Atlantic hurricanes form—two to three of them major—during an average season, which runs from June 1 to November 30.

One of the ways that global warming could reduce hurricanes is by increasing upper-level winds—known as wind shear—that can inhibit hurricane formation, said lead author Thomas Knutson.

The study also suggests that hurricane winds could increase by about 2 percent, and rainfall within 30 miles (48 kilometers) of a hurricane's center could increase by 37 percent.

The study, which appears this week in the journal Nature Geoscience, focuses on the Atlantic Basin, which includes the Gulf of Mexico and the Caribbean Sea.

Recent Data

Knutson said the new study was based on a computer simulation that used hurricane data dating back to 1980.

Detailed data covering a longer period is not available, he added.

"It would be nice if we could run tests based on data all the way back to 1900," Knutson said. "But we don't have adequate large-scale atmospheric data going back that far."

Knutson said NOAA scientists hope to eventually conduct hurricane studies based only on ocean temperatures, which have been tracked reliably for many decades and which would greatly extend the hurricane database.

Hurricanes can form only when water temperatures reach at least 80 degrees Fahrenheit (about 27 degrees Celsius), making ocean data a valuable tool for understanding the dynamics of hurricane formation.

Debate Blows On

The debate over hurricanes and global warming took off in 2005, when a record 28 tropical storms formed in the Atlantic. Several were among the most powerful storms on record, including Hurricane Katrina, which devastated New Orleans.

Some scientists say that the stormy summers of 2004 and 2005 were an indication that global warming is causing more—and more powerful—hurricanes.

Other scientists have said that global warming's effect is minimal, if it exists at all.

Kerry Emanuel, a meteorologist at the Massachusetts Institute of Technology in Cambridge, has been among the scientists who see a direct link between global warming and hurricanes.

The latest NOAA study is "a good study, but the results should be taken with a grain of salt," Emanuel said. "It's good work, but it's premature."

He added that several problems and inconsistencies need to be solved before a reliable evaluation of global warming's effect on hurricanes can be accomplished.

In addition to the scarcity of detailed information about late-19th and early-20th century storms, Emanuel said that variations in how different computer models analyze the same data need to be resolved.

"My feeling is that our understanding of the problem will gradually get better as we pursue all approaches," he said. "It's unlikely that there will be a colossal breakthrough, but it will proceed in steps."

NOAA meteorologist Chris Landsea is science operations officer at the National Hurricane Center in Miami. He did not participate in the study conducted by NOAA's Knutson, but said he thought it was "an excellent new study."

"To me, this reconfirms all of the previous studies that suggest a very tiny change in hurricane intensity and rainfall," Landsea said.

Max Mayfield, hurricane specialist at WPLG-TV in Miami and a former director of the National Hurricane Center, declined to speak on the study's results.

"All I can say," he commented, "is that the debate goes on."

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