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Global Warming Not Boosting Hurricanes

Posted on: Tuesday, 20 May 2008, 15:25 CDT

A distinguished federal scientist has shifted his position regarding the recent increase in hurricanes in the Atlantic ocean, concluding global warming is not the underlying cause. In fact, he believes the warmer temperatures will actually lessen the number of Atlantic hurricanes as well as those making landfall.

The conclusion was made in a report released Sunday by Tom Knutson, a meteorologist with the National Oceanic and Atmospheric Administration's (NOAA) fluid dynamics lab in Princeton, N.J., who had previously raised concerns about the impact of climate change on hurricanes. His new report has the potential to stir a contentious debate among meteorologists about the effects of global warming in the Atlantic.

Hurricanes have often been seen as a sign of global warming’s consequences since Hurricane Katrina hit the gulf coast in 2005. Many climate change experts believe the rise in hurricanes in recent years is due to increased ocean water temperatures caused by global warming. But other experts, including those who study hurricanes and are more skeptical about global warming, say there is no association and attribute the recent increase in hurricanes to natural climate cycles.

What makes this report different is Knutson himself, who in the past had warned about of the perils of climate change and even complained of censorship by the Bush administration on previous research about the dangers of global warming.

His new study, he said, is based on computer models, and presents evidence "against the notion that we've already seen a really dramatic increase in Atlantic hurricane activity resulting from greenhouse warming." The models predict a decrease of 18 percent in the number of hurricanes by the end of the century, and that wind factors will result in a 30 percent drop in the number of hurricanes making landfall in the U.S . and its neighbors west of Puerto Rico.

Knutson’s study also forecasts an 8 percent decrease in the biggest storms, those with winds in excess of 110 mph, while tropical storms with winds between 39 and 73 mph are predicted to fall 27 percent.

However, Knutson’s computer models also predict that hurricanes and tropical storms will be fiercer and more wet, with a 37 percent increase in rainfall within 30 miles and a 2 percent rise in wind strength, which Knutson said his study substantially underestimates.

Some scientists, such as MIT hurricane meteorologist Kerry Emanuel, have been critical of Knutson’s models. While praising Knutson as a scientist, Emanuel said his conclusion was "demonstrably wrong" and was based on a computer model that doesn't properly examine the storms.

Kevin Trenberth, chief climate analyst at the National Center for Atmospheric Research in Boulder, Colo., said Knutson's model improperly assesses tropical weather and "fails to replicate storms with any kind of fidelity." It is not just the number of hurricanes "that matter, it is also the intensity, duration and size, and this study falls short on these issues," he added.

Knutson acknowledges his model’s shortcomings, saying it mainly provides a rough overview and not an accurate view of individual storms and storm strength. The most recent model doesn't produce storms surpassing 112 mph, he said.

But other experts, such as NOAA hurricane meteorologist Chris Landsea, praised Knutson's work as "very consistent with what's being said all along." Landsea was not part of this study.

"I think global warming is a big concern, but when it comes to hurricanes the evidence for changes is pretty darn tiny," he told the Associated Press.

The Atlantic Hurricane season starts June 1, and a Colorado State University report predicts this season to be 50 percent more active than a normal year.
Typically, a normal season will include about 10 named storms, of which six become hurricanes and two become major hurricanes. About five hurricanes strike the United States every three years, on average.

NOAA will release its forecast Thursday.

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On the Net:

A summary of Knutson’s study can be viewed on the NOAA Web site at http://www.noaanews.noaa.gov/stories2008/20080519_hurricanes.html

Nature Geoscience

Source: redOrbit Staff and Wire Reports

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