Increasing ocean temperatures fuelling more powerful hurricanes, say scientists

Katrina-like storms could become more common· Effect 'can't be explained by a natural cycle' Ian Sample, science correspondentTuesday September 12, 2006The Guardian
Hurricane breeding grounds in the Atlantic and Pacific oceans are being warmed by greenhouse gases, raising fears that more intense and devastating storms will be unleashed on nearby coastlines, scientists warned yesterday.
Climate researchers found that emissions from burning fossil fuels and other industrial activities were to blame for driving temperatures upwards in tropical waters where hurricanes form. They predict warmer ocean waters will energise hurricanes and make them more powerful. If sea temperatures continue to rise, scientists fear that category four and five hurricanes, such as Katrina, which battered New Orleans last summer, will become more commonplace.
The scientists, led by Ben Santer at Lawrence Livermore National Laboratory in California, used 22 climate models to investigate the possible causes of a rise in sea surface temperatures of up to 0.67C in the Atlantic and Pacific tropics from 1906 to 2005. Each computer model was run several times to work out how much sea surface temperatures would have warmed with and without rising levels of greenhouse gases and other pollutants.
They found that tiny particulates from volcanos and sulphates from industrial plants blocked the sun, and so cooled the oceans. But the effect was swamped by the rise in greenhouse gases, which led to warmer oceans. The study appears in the latest issue of Proceedings of the National Academy of Sciences.
Nathan Gillett, a co-author of the study at the climatic research unit at the University of East Anglia, said: "We know the oceans have been warming in these regions and some scientists have said it was because of natural events. But this study confirms that it cannot be explained by a natural cycle."
Hurricanes form in tropical waters when evaporating water is sucked up into storms. As the vapour rises, it condenses, releasing energy that fuels the storm. The warmer the ocean surface, the more energy is pumped into the hurricane. "The study suggests that with increasing sea surface temperatures, we can expect more intense hurricanes," Dr Gillett added.
Although the rise in ocean temperatures is slight, it is expected to have a dramatic effect on the intensity of hurricanes. In March Kerry Emanuel, a climate scientist at the Massachusetts Institute of Technology, claimed that while sea temperatures had increased by only about half a degree during the past 30 years, the power of hurricanes had doubled.
Tom Wigley, another scientist on the study, at the National Centre for Atmospheric Research in Boulder, Colorado, added: "The best explanation for these increases has to include a large human influence. We expect global temperatures and sea surface temperatures to increase more rapidly over the next century."