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Friday, April 30, 1999 Published at 11:26 GMT 12:26 UK


Sci/Tech

Severe Arctic ozone hole predicted

The Antarctic ozone hole covers an area of 10 million square miles

Plummeting temperatures high in the Earth's atmosphere are doubling the rate at which the ozone layer is being destroyed, scientists have announced.

The destruction is particularly high over the Arctic and Northern Europe and could lead to an ozone hole as large as the one over the Antarctic.

Ironically, the cooling phenomenon is being blamed on the worldwide increase in greenhouse gases - usually associated with global warming.

An increase in greenhouse gases could cause the cooling because they trap heat in the lowest layer of the atmosphere.

Rapid drop

The layer of the atmosphere called the mesosphere begins 31 miles above the Earth. Here, temperatures have been dropping by a degree Celsius a year for the last three decades. This is ten times faster that anyone had predicted, says New Scientist magazine, which reported the temperature drop.

The cooling of the mesosphere may be a climate warning like the "miner's canary", said Gary Thomas of the University of Colorado. He thinks it is the biggest and most unequivocal sign that the world's climate really is changing.

Below the mesosphere is the stratosphere, which begins nine miles up. Cooling here has been greater than predicted for the last five years. The forecast is that in 20 years the greenhouse effect will have made even the lower stratosphere eight degrees lower.

Ozone destruction

Ozone is affected because pollutants such as CFCs destroy it far faster at low temperatures. The Antarctic ozone hole swells during the winter for this reason.

Decreases in ozone mean that more harmful ultraviolet radiation reaches the Earth's surface. The scientists' study coincided with the announcement in the UK of a new scale of the strength of the sun's rays.

The scale, from one to 20, will be used in weather forecasts to allow people to take appropriate protective measures, depending on their natural skin colour. The UK will score one in winter and around eight in summer. The full glare of the Australian sun would be 18 on the scale.



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