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Wednesday, October 25, 2006

Scientists Further Link Hurricanes, Climate Change

Researchers have linked human activities to rising ocean temperatures in hurricane formation regions, further connecting severe storms to global climate change.

Using 22 different computer models of the climate system, atmospheric scientists from Lawrence Livermore National Laboratory and 10 other labs say that they have shown that the warming of the tropical Atlantic and Pacific oceans over the last century is directly linked to human activities.

For the period 1906-2005, the researchers found an 84 percent chance that external forcing (such as human-caused increases in greenhouse gases, ozone and various aerosol particles) accounts for at least 67 percent of the observed rise in sea surface temperatures (SSTs) in the Atlantic and Pacific hurricane formation regions.

In both regions, human-caused increases in greenhouse gases were found to be the main driver of the 20th century warming of SSTs, the scientists say.

"We’ve used virtually all the world’s climate models to study the causes of SST changes in hurricane formation regions,” says Benjamin Santer of Livermore’s Program for Climate Model Diagnosis and Intercomparison, and lead author of a paper describing the research.

The use of fossil fuels are said to emit greenhouse gases that cause global climate change.

This research shows a further direct link between human activities, climate change and killer storms.

“In the real world, we’re performing an uncontrolled experiment by burning fossil fuels and releasing greenhouse gases,” Santer says. “We don’t have a convenient parallel Earth with no human influence on climate. This is why our study relied on computer models for estimates of how the climate of an ‘undisturbed Earth’ might have evolved. The bottom line is that natural processes alone simply cannot explain the observed SST increases in these hurricane breeding grounds. The best explanation for these changes has to include a large human influence.”

The researchers note that hurricanes are complex phenomena and are influenced by a variety of physical factors such as SST, wind shear, moisture availability and atmospheric stability. The increasing SSTs in the Atlantic and Pacific hurricane formation regions isn’t the sole cause of hurricane intensity, but is likely to be one of the most important influences on hurricane strength.

“The models that we’ve used to understand the causes of SST increases in these hurricane formation regions predict that the oceans are going to get a lot warmer over the 21st century,” Santer says. “That causes some concern. In a post-Katrina world, we need to do the best job we possibly can to understand the complex influences on hurricane intensity, and how our actions are changing those influences.”


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