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Ozone layer hits new depletion record

Blame the weather

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Despite optimism earlier this year that the ozone hole was stabilising and might even have begun to repair itself, scientists at the European Space Agency report that 2006 saw record losses of ozone over the south pole.

Data from ESA's Envisat satellite show that although the area of the ozone hole (this year, 28m square kilometres) is not quite as large as it was in 2000, some 40 million tonnes of ozone were lost during the southern hemisphere winter. This is one million tonnes greater than the previous record from 2000.

The loss is calculated by combining the area of the hole with the depth of the ozone layer. The depth is measured in Dobson units, which describes the thickness of the layer directly over the location being measured, ESA explains.

This year saw the ozone approach the thinnest it has ever been, around 100 dobson units, approaching the record of 1998.

So although it is not as large as the hole in 2000, nor quite as thin as the layer in 1998, the two combined mean the layer has been depleted this year more than ever before.

ESA's atmospheric engineer Claus Zehner explains that the conditions over the Southern pole this year were ideal for depleting the ozone layer:

"Such significant ozone loss requires very low temperatures in the stratosphere combined with sunlight. This year’s extreme loss of ozone can be explained by the temperatures above Antarctica reaching the lowest recorded in the area since 1979," he said.

The Ozone layer, to fill in an unlikely gap in your knowledge, is a protective layer of the atmosphere which absorbs much of the harmful UV from the sun's rays. Its composition naturally fluctuates during the year. It is typically thicker in summer, and thinner in the winter.

The conditions for the hole are set up during the Antarctic winter. In this cold season, a weather pattern known as the polar vortex keeps the atmospheric mass above the Antarctic continent isolated from exchanges with warmer mid-latitude air.

This keeps the air mass above the continent cold, and in the cold and dark, clouds that contain chlorine can form in the polar stratosphere.

Once the spring returns, this chlorine, much of it originating from man-made pollutants like chlorofluorocarbons, disrupts the ozone layer causing the hole with which we are all now so familiar.

Zehner says the current consensus is that the ozone layer will recover from its human induced damage by 2060. Long term measurements, he argues, are key to understanding this process. ®

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