ScienceDaily (Oct. 22, 2007) — Although the ozone layer over the Antarctic this year is relatively small, this is due to mild temperatures in the region’s stratosphere this winter and is not a sign of recovery, the United Nations World Meteorological Organization (WMO) has said.

Since 1998, only the ozone holes of 2002 and 2004 have been smaller than this year’s – both in terms of area and amount of destroyed ozone – and this is not indicative of ozone recuperation, the agency said.

Instead, it is due to mild temperatures in the stratosphere, which still contains sufficient chlorine and bromine to completely destroy ozone in the 14-21 kilometer altitude range.

The amount of gases which diminish ozone in the Antarctic stratosphere peaked around the year 2000. However, despite the decline in the amount by 1 per cent annually, enough chlorine and bromine will be in the stratosphere for another decade or two, which could result in severe ozone holes, WMO said.

The size of the ozone hole will also be determined by the stratosphere’s meteorological conditions during the Antarctic winter. As greenhouse gases accumulate in the atmosphere, temperatures will fall in the stratosphere, increasing the threat of severe ozone holes in the future.

Ozone hole over Antarctica measured in September 2007 by Envisat. The ozone loss in 2007 peaked at 27.7 million tonnes, compared to the 2006 record ozone loss of 40 million tonnes. (Credit: KNMI - ESA)

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