Global warming: Tropical storms revealed as new factor in heat mixBron :
Yahoo.newsWed May 30, 1:40 PM ET
PARIS (AFP) - Hurricanes and typhoons play a significant role in distributing the ocean's heat, say US researchers, who believe they have uncovered a major, but hitherto-ignored aspect of global warming.
Driven by mighty circular winds, cyclones in the western Atlantic, western Pacific and Indian Ocean have long been known to whip up the sea and leave its local surface areas cooler than before.
In a paper appearing on Thursday in Nature, the weekly British science journal, Matthew Huber and Ryan Sriver of Purdue University in Indiana make the first stab at calculating how and where this displaced heat, driven from the surface by the cyclone, ends up.
Their computer model factors in surface sea temperatures before and after a storm's passage, as well as ocean depth and currents.
They found that a cyclone acts rather like the spinning steel blades of a food mixer as it is lowered into a bowl of batter.
The whirling winds so churn the sea that the surface heat is distributed down vertically, towards the depths of the local ocean area, but also circulating it towards the poles.
As much as a seventh of heat transported by the oceans could be linked to cyclones, the paper says.
The finding is important, because future climate change depends to a very high degree on the oceans, which cover two-thirds of the planet's surface and soak up massive amounts of heat from the atmosphere.
The role of cyclones has been overlooked until now, Huber and Sriver believe, because computer models of the world's climate systems only factor in sustained winds that last longer than five days, which would leave out most storms.
Further investigation into cyclone mixing is needed, they say.
If cyclones become more frequent as a result of higher sea temperatures, this in turn will step up the distribution of warm waters to higher latitudes, they warn.
That, in turn, would have plenty of potential for knock-on effects to the climate system.
"Cyclone-induced mixing is a fundamental physical mechanism that may act to stabilise tropical temperatures, mix the upper ocean and cause polar amplification of climate change," the researchers say.
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