Warmer seas linked to strengthening hurricanes: FSU study fuels global warming debate

September 04, 2008

TALLAHASSEE, Fla. -- The theory that global warming may be contributing to stronger hurricanes in the Atlantic over the past 30 years is bolstered by a new study led by a Florida State University researcher. The study will be published in the Sept. 4 edition of the journal Nature.

Using global satellite data, FSU geography Professor James B. Elsner, University of Wisconsin-Madison Professor James P. Kossin and FSU postdoctoral researcher Thomas H. Jagger found that the strongest tropical cyclones are, in fact, getting stronger -- and that ocean temperatures play a role in driving this trend. This is consistent with the "heat-engine" theory of cyclone intensity.

"As seas warm, the ocean has more energy that can be converted to tropical cyclone wind," Elsner said. "Our results do not prove the heat-engine theory. We just show that the data are quite consistent with it."

Kerry Emanuel of the Massachusetts Institute of Technology first suggested the possible connection between global warming and increases in tropical cyclone intensity in a 2005 paper. He linked the increased intensity of storms to the heating of the oceans, which has been attributed to global warming.

Critics argued that the data were not reliable enough to make assertions about the relationship between climate change and hurricanes. Moreover, when scientists looked at the mean tropical cyclone statistics, they did not see an upward trend.

Elsner's team addressed both issues by using globally consistent, satellite-derived tropical cyclone wind speeds as opposed to the observational record and by focusing on the highest wind speeds of the strongest tropical cyclones each year.

Emanuel's theory is that the intake of warm air near the ocean surface and the exhaust of colder air above the cyclone is what drives a hurricane. Other factors being equal, the warmer the ocean, the warmer the intake of air. This heat-engine theory of how hurricanes increase their intensity is well accepted, but there are many environmental factors, such as wind shear, that might prevent a hurricane from strengthening, Elsner said.

To address that problem, Elsner's team looked at a subset of hurricanes that are closest to their maximum possible intensity (MPI). Under the heat-engine theory, every storm will lose some energy through inefficiency, and that loss will limit the storm's potential. The MPI represents the storm's maximum potential under ideal environmental conditions.

"We speculated that you might not see a trend in the intensity of typical hurricanes due to environmental factors, but if the heat-engine theory is correct, you should see a trend in the intensity of hurricanes at or near their MPI," Elsner said. "On average, the strongest storms are closest to their MPI."

The researchers created a data set from satellite observations of hurricane intensity of all tropical cyclones around the globe and looked at the maximum wind speeds for each one during a 25-year period. Tropical cyclones, which include hurricanes, typhoons and tropical storms, occur on average about 90 times per year worldwide.

The researchers found that the strongest tropical cyclones are getting stronger, particularly over the North Atlantic and Indian oceans. Wind speeds for the strongest tropical storms increased from an average of 140 mph in 1981 to 156 mph in 2006, while the ocean temperature, averaged globally over the all regions where tropical cyclones form, increased from 28.2 degrees Celsius to 28.5 degrees Celsius during this period.

"By creating a better, more consistent historical data set, we've been able to weed out quality issues that introduce a lot of uncertainty," Kossin said. "Then, by looking only at the strongest tropical cyclones, where the relationship between storms and climate is most pronounced, we are able to observe the increasing trends in storm intensity that both the theory and models say should be there."

While Elsner said the heat-engine theory might explain how tropical cyclones intensify given that everything else is the same, he noted, "We still do not have a complete understanding of why some cyclones intensify, sometimes quite rapidly, and others don't."

Florida State University

---

---

	Hurricanes! by Gail Gibbons (Author) Imagine a force that can toss boats around like toys, wash away bridges, and create waves as high as eighteen feet. With fierce winds and torrential rains, hurricanes can do all of these things. They can cause tremendous damage and even change the shape of a shoreline. For centuries people did not know when a hurricane was coming. But now we have new methods to predict when and where these storms will occur. Young readers will learn how hurricanes are formed, how they are named and classified, and what to do if a dangerous storm is on the way.
	Hurricanes by Seymour Simon (Author) Hurricanes. Typhoons. Cyclones. No matter what you call them, these formidable, swirling storms are the most devastating events in nature. hurricanes takes young readers on an in-depth exploration of one of the most awe-inspiring phenomena on Earth! This dramatic account of hurricanes and the disasters they leave behind, including Andrew and Katrina, are intensified through arresting full-color photographs and satellite images. Award-winning science writer Seymour Simon has teamed up with the Smithsonian Institution to bring you a new, updated edition of his acclaimed look at this astonishing, and often terrifying, natural disaster.
	DK Eyewitness Books: Hurricane and Tornado by Jack Challoner (Author) New Look! Relaunched with new jackets and 8 pages of new text! Here is a dramatic and compelling guide to nature's most dangerous and destructive forces. Stunning full-color photographs, models and illustrations offer a unique "eyewitness" view of catastrophic weather conditions. See into the eye of a spiraling cyclone, hailstones the size of tennis balls, a spectacular lightning ball, the devastating effects of the El Nino phenomenon, and how a gentle mountain stream can become a raging torrent within a few minutes. Learn the techniques developed through the centuries to forecast weather, about the chicken that was stripped of its feathers by a tornado, about Benjamin Franklin's lightning rod, and why human activity can cause weather patterns to change. Discover what causes...
	Hurricane Warning by MuseItUp Publishing A hurricane! Just what Linda Morrison needs to welcome her to her new home in Florida. Fearing her recent purchase may end up a bundle of sticks, she’s relieved when a hero swoops in wearing a yellow slicker and offering help. Carlos Mejia is eye candy for sure, but she needs those muscles to help board up the window. Together they ride out the storm raging outside, but inside there’s more than a little electricity in the air.
	I Survived Hurricane Katrina, 2005 by Lauren Tarshis (Author) The horror of Hurricane Katrina is brought vividly to life in this fictional account of a boy, a dog, and the storm of the century. Barry's family tries to evacuate before Hurricane Katrina hits their home in New Orleans. But when Barry's little sister gets terribly sick, they're forced to stay home and wait out the storm. At first, Katrina doesn't seem to be as bad as predicted. But overnight the levees break, and Barry's world is literally torn apart. He's swept away by the floodwaters, away from his family. Can he survive the storm of the century -- alone?
	Sudden Sea: The Great Hurricane of 1938 by R.A. Scotti (Author) It was the Perfect Storm. But instead of raging far out in the Atlantic, the Great Hurricane of 1938 left a wake of death and destruction across seven states. It battered J. P. Morgan's Long Island estate, wiped out beach communities from Watch Hill to Newport, flooded the Connecticut Valley, and flattened Vermont's prized maples.Traveling at record speeds, the storm raced up the Atlantic Coast, reaching New York and New England ahead of hurricane warnings and striking with such ferocity that seismographs in Alaska picked up the impact. Winds, clocked at 186 mph, stripped cars of their paint. Walls of water 50 feet high swept homes and entire families out to sea. Sandwiched between the Great Depression and World War II, the storm had a profound impact upon a generation. 'The day of the...
	Hurricanes! (Hello Reader) by Lorraine J. Hopping (Author) Introduces early readers to hurricanes by revealing how these powerful storms form, describing what happens during a hurricane, and explaining how they are studied.
	Infinite Monster: Courage, Hope, and Resurrection in the Face of One of America's Largest Hurricanes by Leigh Jones (Author), Rhiannon Meyers (Author) Critical Praise for Infinite Monster ''Infinite Monster is a deeply moving, harrowing account of one America's great cities--Galveston--being ravaged by Hurricane Ike. Highly recommended!'' ---Douglas Brinkley, professor of History at Rice University and author of The Great Deluge: Hurricane Katrina, New Orleans, and the Mississippi Gulf Coast ''Infinite Monster deserves a place alongside Isaac's Storm and A Weekend in September as a tale of a star-crossed city's struggle to endure the ravages of a mammoth hurricane. Leigh Jones' and Rhiannon Meyers' meticulous reporting chronicles the dramatic personal stories that took place on the night Hurricane Ike made landfall and the controversial decisions that had to be made in the storm's aftermath.'' ---Paul Burka, Senior Executive Editor,...
	The Magic School Bus Inside A Hurricane by Joanna Cole (Author), Bruce Degen (Illustrator), Bruce Degan (Illustrator) To celebrate its 20th anniversary, Scholastic is re-releasing the ten original Magic School Bus titles in paperback. With updated scientific information, the bestselling science series ever is back! Count on Ms. Frizzle to teach anything but an ordinary lesson on meteorology. Flying through the clouds in the Magic School Bus, Ms. Frizzle's class experiences a hurricane-and even a tornado-firsthand. During their thrilling ride through the sky, Arnold gets lost! Will the Friz be able to save the day this time?
	Hurricane Watch: Forecasting the Deadliest Storms on Earth by Jack Williams (Author), Bob Sheets (Author) The ultimate guide to the ultimate storms, Hurricane Watch is a fascinating blend of science and history from one of the world's foremost meteorologists and an award-winning science journalist. This in-depth look at these awe-inspiring acts of nature covers everything from the earliest efforts by seafarers at predicting storms to the way satellite imaging is revolutionizing hurricane forecasting. It reveals the latest information on hurricanes: their effects on ocean waves, the causes of the variable wind speeds in different parts of the storm, and the origins of the super-cooled shafts of water that vent at high altitudes. Hurricane Watch is a compelling history of man's relationship with the deadliest storms on earth. Includes: - The story of the nineteenth-century...