Warming May Reduce Hurricane Landfalls, Study Says

Seth Borenstein, AP Science Writer
Associated Press

January 23, 2008

Contrary to many previous reports, global warming could reduce the number of hurricanes that strike the United States, according to a new study.

The work is the latest in a contentious scientific debate over how human-induced global warming might affect the intensity and frequency of hurricanes.

In the study, researchers from the National Oceanic and Atmospheric Administration and the University of Miami in Florida link warming oceans to increased vertical wind shear in the Atlantic Ocean near the United States.

Wind shear—a change in upper-level wind speed or direction—makes it hard for hurricanes to form, strengthen, and stay active.

With every degree Celsius that the oceans warm, the wind shear increases by up to 10 miles (16 kilometers) an hour, said lead study author Chunzai Wang, a physical oceanographer at NOAA.

So that means "global warming may decrease the likelihood of hurricanes making landfall in the United States," according to the study authors.

Global Effects

The NOAA findings support results released last April in which a suit of climate models also predicted an increase in wind shear due to warming.

The new study is based on observations instead of computer models, Wang noted.

Observations made between 1854 to 2006 show that sea-surface temperatures are rising globally, his team says, with significant warming in the tropical regions of the Pacific, Atlantic, and Indian oceans.

Ocean temperatures in the tropical Pacific and Indian oceans have global effects, much like the Pacific weather phenomenon known as El Niño does, Wang said.

Warming in those regions will increase wind shear in the areas of the Atlantic where hurricanes form.

This effect could counterbalance a predicted increase in major hurricanes due to rising ocean temperatures.

The study appears today in the journal Geophysical Research Letters.

Heated Debate

But critics say Wang's study is based on poor data that was rejected by scientists on the Nobel Prize-winning Intergovernmental Panel on Climate Change (IPCC).

Reports released by the IPCC say that "more likely than not" human-caused global warming has already increased the frequency of the most intense storms.

At times only one in ten North Atlantic hurricanes hit the U.S. coast, critics add, and the data reflect only a small percentage of storms around the globe.

Hurricanes hitting land "are not a reliable record" for how the storms have changed, said Kevin Trenberth, climate analysis chief for the National Center for Atmospheric Research in Boulder, Colorado.

In 2006 Trenberth co-authored a study that said global warming was the main factor in the record-breaking 2005 Atlantic hurricane season, which included Hurricane Katrina.

Another group of climate scientists has linked global warming to increases in the strongest hurricanes—just those with winds greater than 130 miles (kilometers) an hour—over the past 35 years.

But some hurricane researchers, especially scientists at NOAA's Miami Lab, have argued that the long-term data for all hurricanes show no such trend.

And Wang's new research suggests just the opposite.

Regardless of which side turns out to be right, it only takes one storm to be deadly, said former National Hurricane Center director Max Mayfield.

So the key for residents of hurricane-prone areas, he said, is to be prepared for a storm "no matter what."

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