Featured Research

from universities, journals, and other organizations

Hurricanes Are Getting Stronger, Study Says

Date:
September 16, 2005
Source:
National Center For Atmospheric Research
Summary:
The number of Category 4 and 5 hurricanes worldwide has nearly doubled over the past 35 years, even though the total number of hurricanes has dropped since the 1990s, according to a study by researchers at the Georgia Institute of Technology and the National Center for Atmospheric Research (NCAR). The shift occurred as global sea surface temperatures have increased over the same period.

Hurricane Katrina reached Category 5 status on August 28 while churning across the Gulf of Mexico before making landfall the next day at Category 4. The result along the Mississippi gulf coast was damage and destruction like that in Biloxi, shown above. Three hurricanes had already attained Category 4 or 5 status across the gulf by the end of August, an unprecedented total for so early in the season.
Credit: Photo courtesy FEMA/Mark Wolfe

BOULDER -- The number of Category 4 and 5 hurricanes worldwide has nearly doubled over the past 35 years, even though the total number of hurricanes has dropped since the 1990s, according to a study by researchers at the Georgia Institute of Technology and the National Center for Atmospheric Research (NCAR). The shift occurred as global sea surface temperatures have increased over the same period. The research appears in the September 16 issue of Science.

Peter Webster, professor at Georgia Tech's School of Earth and Atmospheric Sciences, along with NCAR's Greg Holland and Georgia Tech's Judith Curry and Hai-Ru Chang, studied the number, duration, and intensity of hurricanes (also known as typhoons or tropical cyclones) that have occurred worldwide from 1970 to 2004. The study was supported by the National Science Foundation (NSF), NCAR's primary sponsor.

"What we found was rather astonishing," said Webster. "In the 1970s, there was an average of about 10 Category 4 and 5 hurricanes per year globally. Since 1990, the number of Category 4 and 5 hurricanes has almost doubled, averaging 18 per year globally."

Category 4 hurricanes have sustained winds from 131 to 155 miles per hour; Category 5 systems, such as Hurricane Katrina at its peak over the Gulf of Mexico, feature winds of 156 mph or more.

"This long period of sustained intensity change provides an excellent basis for further work to understand and predict the potential responses of tropical cyclones to changing environmental conditions", said NCAR's Holland.

"Category 4 and 5 storms are also making up a larger share of the total number of hurricanes," said Curry, chair of the School of Earth and Atmospheric Sciences at Georgia Tech and coauthor of the study. "Category 4 and 5 hurricanes made up about 20% of all hurricanes in the 1970s, but over the last decade they accounted for about 35% of these storms."

The largest increases in the number of intense hurricanes occurred in the North Pacific, Southwest Pacific, and the North and South Indian Oceans, with slightly smaller increases in the North Atlantic Ocean.

All this is happening as sea surface temperatures have risen across the globe between one-half and one degree Fahrenheit, depending on the region, for hurricane seasons since the 1970s.

"Our work is consistent with the concept that there is a relationship between increasing sea surface temperature and hurricane intensity," said Webster. "However, it's not a simple relationship. In fact, it's difficult to explain why the total number of hurricanes and their longevity has decreased during the last decade, when sea surface temperatures have risen the most."

"NCAR is now embarking on a focused series of computer experiments capable of resolving thunderstorms and the details of tropical cyclones," said Holland. "The results will help explain the observed intensity changes and extend them to realistic climate change scenarios."

The only region that is experiencing more hurricanes and tropical cyclones overall is the North Atlantic, where they have become more numerous and longer-lasting, especially since 1995. The North Atlantic has averaged eight to nine hurricanes per year in the last decade, compared to six to seven per year before the increase. Category 4 and 5 hurricanes in the North Atlantic have increased at an even faster clip: from 16 in the period of 1975-89 to 25 in the period of 1990-2004, a rise of 56%.

A study published in July in the journal Nature came to a similar conclusion. Focusing on North Atlantic and North Pacific hurricanes, Kerry Emanuel (Massachusetts Institute of Technology) found an increase in their duration and power, although his study used a different measurement to determine a storm's power.

But whether all of this is due to human-induced global warming is still uncertain, said Webster. "We need a longer data record of hurricane statistics, and we need to understand more about the role hurricanes play in regulating the heat balance and circulation in the atmosphere and oceans."

"Basic physical reasoning and climate model simulations and projections motivated this study," said Jay Fein, director of NSF's climate and large scale dynamics program, which funded the research. "These results will stimulate further research into the complex natural and anthropogenic processes influencing these tropical cyclone trends and characteristics."

Webster is currently attempting to determine the basic role of hurricanes in the climate of the planet. "The thing they do more than anything is cool the oceans by evaporating the water and then redistributing the oceans' tropical heat to higher latitudes," he said.

"But we don't know a lot about how evaporation from the ocean surface works when the winds get up to around 100 miles per hour, as they do in hurricanes," said Webster, who adds that this physical understanding will be crucial to connecting trends in hurricane intensity to overall climate change.

"If we can understand why the world sees about 85 named storms a year and not, for example, 200 or 25, then we might be able to say that what we're seeing is consistent with what we'd expect in a global warming scenario. Without this understanding, a forecast of the number and intensity of tropical storms in a future warmer world would be merely statistical extrapolation."

Related Sites

NCAR Tip Sheet: Hurricane Prediction, Behavior, and Impacts -- http://www.ucar.edu/news/releases/2005/hurricanetips.shtml

Georgia Institute of Technology - School of Earth and Atmospheric Sciences -- http://www.eas.gatech.edu/


Story Source:

The above story is based on materials provided by National Center For Atmospheric Research. Note: Materials may be edited for content and length.


Cite This Page:

National Center For Atmospheric Research. "Hurricanes Are Getting Stronger, Study Says." ScienceDaily. ScienceDaily, 16 September 2005. <www.sciencedaily.com/releases/2005/09/050916072459.htm>.
National Center For Atmospheric Research. (2005, September 16). Hurricanes Are Getting Stronger, Study Says. ScienceDaily. Retrieved April 19, 2014 from www.sciencedaily.com/releases/2005/09/050916072459.htm
National Center For Atmospheric Research. "Hurricanes Are Getting Stronger, Study Says." ScienceDaily. www.sciencedaily.com/releases/2005/09/050916072459.htm (accessed April 19, 2014).

Share This



More Earth & Climate News

Saturday, April 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Drought Concerns May Hurt Lake Tourism

Drought Concerns May Hurt Lake Tourism

AP (Apr. 18, 2014) Operators of recreational businesses on western reservoirs worry that ongoing drought concerns will keep boaters and other visitors from flocking to the popular summer attractions. (April 18) Video provided by AP
Powered by NewsLook.com
First Ever 'Female Penis' Discovered In Animal Kingdom

First Ever 'Female Penis' Discovered In Animal Kingdom

Newsy (Apr. 18, 2014) Not only are these newly discovered bugs' sex organs reversed, but they also mate for up to 70 hours. Video provided by Newsy
Powered by NewsLook.com
Ark. Man Finds 6-Carat Diamond At State Park

Ark. Man Finds 6-Carat Diamond At State Park

Newsy (Apr. 18, 2014) An Arkansas man has found a nearly 6.2-carat diamond, which he dubbed "The Limitless Diamond," at the Crater of Diamonds State Park. Video provided by Newsy
Powered by NewsLook.com
Deadly Avalanche Sweeps Slopes of Mount Everest

Deadly Avalanche Sweeps Slopes of Mount Everest

AP (Apr. 18, 2014) At least six Nepalese guides are dead after an avalanche swept the slopes of Mount Everest along a route used to climb the world's highest peak. (April 18) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins