Jet Stream Shifts May Spur More Powerful Hurricanes

Willie Drye
for National Geographic News
April 24, 2008
Earth's jet streams—high-altitude winds that influence storm direction—may be changing due to global warming, possibly making it easier for hurricanes to form, a new study says.

Jet streams in both the Northern and Southern Hemispheres have moved toward the poles and are slightly higher now than they were in 1979, according to analyses of data collected between 1979 to 2001.

Researchers also discovered that the jet stream in the Northern Hemisphere, which can affect the formation of hurricanes over the Atlantic Ocean, is a little weaker than it was two decades ago.

More studies are needed to conclusively link the shifts to global warming, the scientists say.

(Related: "Hurricanes Have Doubled Due to Global Warming, Study Says" [July 30, 2007].)

All Speculation

When upper-level winds are present during the hurricane season, the gusts can create wind shear, which greatly inhibits storm formation.

That's because winds blow across the top of the hurricane, preventing the storm's circulation from gaining the momentum it needs to develop more power. The jet stream also sometimes steers storms away from the U.S. mainland.

But without these upper-level winds to inhibit the storms' development, stronger and more plentiful Atlantic hurricanes could form and make landfall in the U.S.

(See photos of hurricanes' destruction.)

However the possible effects of jet stream shifts on hurricanes is only briefly mentioned in the study and is "all speculation," said study co-author Christina Archer, a meteorologist at the Carnegie Institution's Department for Global Ecology in Stanford, California.

Archer and colleague Ken Caldeira, also of Carnegie, published their research recently in the journal Geophysical Research Letters.

There are several possible reasons why the jet streams are moving, the authors note.

"It could be part of a natural cycle. Or [it's] just a random fluctuation and we happened to pick a time of random fluctuation," Caldeira said.

"Or it could be caused by global warming."

Kerry Emanuel, a meteorologist at the Massachusetts Institute of Technology in Cambridge, was not involved in the study.

Emanuel said the analysis and results of the new research seem reasonable.

"My guess is that the most important effect on hurricanes would be on their paths. The shift could mean that more hurricanes make landfall along the U.S. East Coast and Gulf Coast."

But Emanuel also noted that an April 2007 study based on computer simulations theorized that wind shear is increasing, and that could cut down on hurricane formation.

Global Warming Debate

The new research could add to the debate about whether global warming is having an effect on hurricane formation.

(Related: "Hurricanes to Be Sapped, Not Strengthened, by Warming?" [April 18, 2007].)

Keith Blackwell, a meteorologist at the University of South Alabama's Coastal Weather Research Center in Mobile, was also not involved in the study.

"The planet appears to be warming, but I think the jury is still out on the cause," Blackwell said.

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