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Friday, September 25, 1998 Published at 01:33 GMT 02:33 UK


Vicious circles

Satellite image on 2 September shows Hurricanes Isis, Earl and Danielle (from left to right)

Richard Black of BBC Science explains:
Scientists have discovered that hurricanes contribute to global warming by transferring carbon dioxide from the ocean to the atmosphere.

Climate models indicate that global warming will make hurricanes more frequent, so this newly-discovered process could make climate change accelerate once it is started.

The reason for this, say scientists in this week's edition of the journal Nature, is that the winds inside a hurricane are so violent they literally pull carbon dioxide from the sea's surface.

Once in the atmosphere, it adds to global warming.

So the more hurricanes there are, the more there will be.

Power to destroy and kill

Hurricanes occur when the energy of hot and wet tropical air collides with cooler and dry air. The resultant storm has the power to wreak havoc, causing death and destruction.

[ image: Extensive flooding followed Hurricane Bonnie in August]
Extensive flooding followed Hurricane Bonnie in August
At its centre is a calm sunlit eye, measuring tens of kilometres across.

Beyond the eye, winds can reach up to 200mph with torrential rain.

One of the worse hurricanes was Andrew in 1992, which killed 54 people and left insurance companies in the UK with a £15bn bill.

Hurricane Fran in September 1996 caused up to $3bn damage.

The worst British hurricane was the Channel Storm of November 1703, in which 8,000 people were reportedly killed.

The spate of hurricanes and other weather-related catastrophes has been blamed by some meteorologists on the El Nino phenomenon.

'More frequent and more intense'

Humans put about 12 times as much carbon dioxide into the air each year as hurricanes do, to put it into context.

But that could change with computer models predicting that as our planet's surface warms up hurricanes will probably become more frequent and more intense.

Which in turn means they will draw more carbon dioxide from the oceans.

This is what scientists call a "positive feedback" mechanism - a result of a process which in turn reinforces that process.

Several other positive feedback mechanisms have already been discovered relating to global warming. For example, ice reflects heat back into space and so cools the Earth.

But as the Earth gets warmer there will be less ice.

Warming will make weather patterns more extreme - more droughts and more floods, making life more difficult for plants which absorb carbon dioxide.

Regions of permafrost, permanently-frozen ground, will start to melt, releasing methane which is a greenhouse gas. And so on.

Each of these processes on their own might not intensify global warming very much.

But the more such processes we discover, the more the idea gains ground that at some time in the future, the current heating of the Earth could run out of control.

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