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NOAA image of global warming’s multiple influences on hurricanes.April 17, 2007 Global climate model simulations for the 21st Century indicate a robust increase in vertical wind shear in the tropical Atlantic and East Pacific Oceans, which could act to inhibit the development or intensification of hurricanes in these regions. Historically, increased vertical wind shear has been associated with reduced hurricane activity and intensity. (Click NOAA image for larger view of global warming’s multiple influences on hurricanes. Click here for high resolution version. Please credit “NOAA.”)

This new finding is reported in a study by scientists at the NOAA Geophysical Fluid Dynamics Laboratory in Princeton, N.J., and the Rosenstiel School of Marine and Atmospheric Science at the University of Miami, scheduled to be published April 18 in Geophysical Research Letters.

While other studies have linked hurricane intensity to global warming, this is the first published study to indicate that changes to vertical wind shear seen in future climate projections would likely diminish the frequency and intensity of hurricanes. Some effects of global warming, such as coral bleaching and melting tundra, are better understood than the impact on hurricanes.

"Wind shear is one of the dominant controls of hurricane activity, and the models project substantial increases in the Atlantic," said Gabriel Vecchi, lead author of the paper and a NOAA research oceanographer at GFDL. "Based on historical relationships, the impact of the projected shear change could be comparable in magnitude as that of the warming oceans—with the opposite effect."

NOAA image of the Pacific Walker Circulation.Examining possible impacts of anthropogenic greenhouse warming on hurricane activity, the researchers used climate modeling to assess large-scale environmental factors tied to hurricane formation and intensity. They focused on projected changes in vertical wind shear over the tropical Atlantic and how those changes tie to the Pacific Walker circulation. The Walker circulation is a vast loop of winds that influences climate across much of the globe, and varies during El Niño and La Niña oscillations. (Click NOAA image for larger view of the Pacific Walker Circulation. Click here for high resolution version. Please credit “NOAA.”)

By reviewing results from 18 different models, the authors identified a robust increase in wind shear over the tropical Atlantic and East Pacific attributable to global warming. Multiple models, in close agreement, project long-term increases in vertical wind shear, which are closely linked to a weakened Walker circulation over this century. Their research suggests that the increase in vertical wind shear could inhibit both hurricane development and intensification.

"The models send a fairly clear message that we can't dismiss vertical wind shear as we look at the long-term effect of global warming on hurricanes," Vecchi said. He also noted that the model projections of an increased wind shear are confined to the tropical Atlantic and East Pacific, and that factors other than global warming contribute to change in Atlantic wind shear. "This doesn't settle the issue. It's one piece of the puzzle that will contribute to what is an incredibly active field of research."

The analysis was carried out at GFDL with a mid-range emissions scenario from the recent Intergovernmental Panel on Climate Change report, using 18 state-of-the-art global coupled ocean-atmosphere models. The northern Atlantic hurricane season was considered during two 20-year periods in the 21st century, 2001-2020 and 2081-2100.

"This study does not, in any way, undermine the widespread consensus in the scientific community about the reality of global warming," said co-author Brian Soden, Rosenstiel School associate professor of meteorology and physical oceanography whose research is partly funded by NOAA. "In fact, the shear changes are driven by global warming."

The Geophysical Fluid Dynamics Laboratory advances NOAA's expert assessments of changes in national and global climate through research, improved models and products. The goal of GFDL's research is to understand and predict the Earth's climate and weather, including the impact of human activities.

NOAA, an agency of the U.S. Commerce Department, is celebrating 200 years of science and service to the nation. From the establishment of the Survey of the Coast in 1807 by Thomas Jefferson to the formation of the Weather Bureau and the Commission of Fish and Fisheries in the 1870s, much of America's scientific heritage is rooted in NOAA. NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and information service delivery for transportation, and by providing environmental stewardship of the nation's coastal and marine resources. Through the emerging Global Earth Observation System of Systems (GEOSS), NOAA is working with its federal partners, more than 60 countries and the European Commission to develop a global monitoring network that is as integrated as the planet it observes, predicts and protects.

Relevant Web Sites
NOAA Visualizations of Increased Shear (Graphics and Animations)

NOAA Geophysical Fluid Dynamics Lab

Media Contact:
Jana Goldman, NOAA Research, (301) 734-1123 or Maria Setzer, NOAA Geophysical Fluid Dynamics Lab, (609) 452-6643