Global Warming Tied To More Intense Hurricanes

by Stephen Leahy

(IPS) -- As many as 12 more Atlantic tropical storms, four of them major hurricanes, are expected this year, according to the U.S. National Oceanographic and Atmospheric Administration (NOAA).

"This may well be one of the most active Atlantic hurricane seasons on record, and will be the ninth above-normal Atlantic hurricane season in the last 11 years," Brig. Gen. David L. Johnson, director of the NOAA National Weather Service, said in a statement.

NOAA forecasts a whopping 21 tropical storms -- double the norm -- before the end of hurricane season on Nov. 30. That means the U.S, Mexico and Caribbean region could still be pounded by another 10 to 12 storms, including a major hurricane on the scale of Katrina. Fortunately, not all of these are likely to make landfall.

Warm water in the Atlantic Ocean is being blamed. Seawater at 27 degrees Celsius or higher (81 degrees Fahrenheit) puts enough moisture in the air to prime hurricane or cyclone formation. Once started, a hurricane needs only warm water and the right wind conditions to build and maintain its strength and intensity.

When Hurricane Katrina first hit southern Florida last week, it was just Category One on the Saffir-Simpson scale, which rates hurricanes from one to five according to wind speeds and destructive potential. Less than 24 hours after it entered the warm waters of the Gulf of Mexico, it quickly gained strength, becoming a Category Five with winds blowing continuously above 250 kilometers an hour.

While Katrina lost strength to a Category Four when it hit the U.S. Gulf Coast, it was extremely large in size, cutting a broad swath of destruction. The city of New Orleans is evacuated because of severe flooding.

"There's no question that the warm waters of the Gulf provided the heat that turned Katrina into a major storm," said Ross Gelbspan, a Pulitzer Prize-winning reporter and author of two books on global warming.

The ultimate cause, however, is global warming, Gelbspan told IPS.

That's a controversial view in a country with many officials who vigorously deny the existence of global warming or climate change. But scientific evidence -- and the numerous record-breaking storms, droughts, floods and forest fires -- suggest that the climate is indeed changing.

Climatologist David Easterling of NOAA's National Climatic Data Center has found that rainfall intensity in the U.S. has increased significantly, which he attributes to climate change. However, whether the currently warmer mid-Atlantic is the result of global warming or a natural cycle "is pretty hard to say," he said.

On a global scale, there is clear evidence of human-produced warming of the world's oceans, said Tim Barnett, a marine physicist at Scripps Institution of Oceanography in California.

"The amount of heat that has gone into the oceans is truly remarkable," Barnett said in a statement.

Over the last 40 years, the top 300 meters of the world's oceans have warmed about a half-degree Celsius on average. Although that's not a new finding, Barnett is the first to say he has proved it is the result of emissions of greenhouse gases from burning fossil fuels.

Using a combination of computer models and real-world "observed" data, scientists say they measured for the first time the impact of global warming in the oceans.

"This is perhaps the most compelling evidence yet that global warming is happening right now," Barnett said.

And according to another landmark study the warmer ocean is pumping up the destructive power of hurricanes and typhoons. The global increase in ocean temperature has resulted in a doubling of the destructive power of North Atlantic hurricanes, Kerry Emanuel of the Massachusetts Institute of Technology wrote in July in the journal Nature.

In the other region Emanuel studied, storms in the northwest Pacific Ocean are 75 percent more powerful than they were 30 years ago.

Emanuel measured the wind speed of storms and their duration to produce an analysis of the destructive potential of each storm. Actual destruction was not measured because most storms do not make landfall.

He found no evidence for an increase in the number of storms.

Other studies have shown that global warming is creating conditions that are more favorable for hurricanes to develop and be more severe.

Predictions made about climate change 10 years ago are coming true: sea level and temperature rise, increased air temperatures, and now increased storm intensity.

It is well past time for the U.S. to take action on climate change and follow the lead of Britain and Germany with dramatic cuts in emissions of 60 percent, says Gelbspan.

"We don't need to wait for another 10 years of studies before reducing emissions as the Bush administration suggests," says Michael Mastrandrea, an environmental science and policy researcher at Stanford University.

"Waiting to start making major reductions in emissions runs the risk of triggering irreversible impacts," Mastrandrea told IPS.

Because there is a long lag in the climate system, the full effects of past greenhouse gas emissions are yet to come, he said. Adding ever higher levels of emissions puts future generations at risk.

"We should hedge our bets and act now," Mastrandrea said.