Study: Severe Hurricanes Increasingly Common

A new study published in Science magazine shows powerful hurricanes have become more common over the past 35 years. Storms are more likely to develop into dangerous Category 4 or 5 hurricanes. Scientists attribute this to a global trend of warmer ocean waters.

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A new study shows powerful hurricanes are becoming more common. They are more likely to be Category 4 or 5, the strongest storms. Scientists attribute this to a global trend of warmer ocean waters. NPR's Richard Harris reports.

RICHARD HARRIS reporting:

There's no question the number of hurricanes hitting the United States has increased substantially in the past decade. Some scientists have said this is nothing more than part of a normal cycle. Others have suggested it might be part of a worldwide trend, due to global warming.

Mr. PETER WEBSTER (Georgia Tech): We were rather worried that people were looking locally and inferring globally and we thought that was the wrong way to go.

HARRIS: Peter Webster and his colleagues at Georgia Tech figured if rising global temperatures are affecting hurricane activity, that should be noticeable on a global scale, not just in the North Atlantic. So they tracked down satellite images of hurricanes for the past 35 years and looked for trends. The results are published in Science magazine. And it's absolutely true that hurricane activity has picked up markedly in the North Atlantic, but Webster says that's not true globally.

Mr. WEBSTER: At all the other ocean basins, their hurricane number has sort of stayed around much the same or decreased slightly in the last 10, 15 years.

HARRIS: So there has been no increase in the total number of hurricanes, but there have been more strong hurricanes and fewer weak ones in the past decade.

Mr. WEBSTER: In all of the basins, including the Atlantic Ocean, the number of Category 4 and Category 5 hurricanes since 1995 have doubled compared to the 1970s and the early '80s.

HARRIS: Webster says there's a plausible reason for this. Hurricanes draw heat out of the oceans as they build, and the sea surface temperature in the tropics has warmed by 1 degree since 1972. That may sound like a very small number, but it represents a huge amount of energy.

Mr. WEBSTER: And the interesting thing about when the sea surface temperature gets warmer, it's like the octane level of the fuel becomes higher and higher because, as you get warmer, you start to evaporate more and more moisture.

HARRIS: Because of this, some scientists have predicted that the biggest hurricanes will become even bigger, with faster and more ferocious maximum winds.

Mr. WEBSTER: We're not seeing that, at least in the satellite observations that we have.

HARRIS: Still, Webster says that he is seeing a global increase in big storms. It's not just a regional trend. So he suspects there's a global cause, and that would be global warming heating up the surface of the world's oceans. But Roger Pielke Jr. at the University of Colorado is worried about making that link.

Mr. ROGER PIELKE Jr. (University of Colorado): We should be worrying about climate change. It's a very important problem. And we should be worried about hurricane impacts. What we shouldn't do is try to confuse those two issues as if they were one in the same.

HARRIS: Pielke argues that the way to reduce the damage done by hurricanes is to focus on what's on the shore, not what's in the atmosphere.

Mr. PIELKE: Even if we take at face value the current scientific consensus on hurricanes and climate change, it is not as large a factor as people moving more and more to the coast and getting wealthier and wealthier, putting more structures in harm's way.

HARRIS: He figures for every extra dollar of damage caused by stronger storms, there will be $20 to $60 of added damage due to coastal development. Pielke recognizes that Hurricane Katrina provides an opportunity to talk about the link between climate change and extreme weather.

Mr. PIELKE: Often, windows of opportunity for policy change occur in the aftermath of disasters. But I think from a standpoint of democracy, pure and simple, we have to be very careful that the justifications that are put forward for policy action are well-matched with the reality on the ground.

HARRIS: Remember, he says, more mammoth hurricanes like Katrina will strike our shores in the coming decades, global warming or no.

Richard Harris, NPR News, Washington.

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World leaders are urging the United Nations to play a bigger role in everything from fighting terrorism to easing the effects of high oil prices. The calls for action come as the UN General Assembly wraps up a three-day summit in New York. UN delegates have heard a series of speeches from world leaders, including a fiery address yesterday by Venezuelan President Hugo Chavez, who scolded President Bush for the war in Iraq and suggested the UN move its headquarters to another country. Later today, the 191 UN member states are expected to adopt a document that includes steps to tackle poverty and reform the UN.

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