Ozone hole over Antarctica continues

by Someshwar Singh

Geneva, Sep 1 -- The periodic ozone hole over the Antarctica has begun to widen again this year and is likely to reach its peak size by early October, according to the World Meteorological Organization (WMO), the UN specialized agency based in Geneva.

Already at over eight million square kilometres, about the size of Europe, the depletion of the stratospheric ozone accelerates during the first half of September and the lowest ozone values are reached toward the end of September and in early October.

"The last 10 days in August have seen very significant declines and this is expected to continue in the future," said Dr. Rumen D. Bojkov of WMO. "In six of the last ten years, the decline of the ozone layer over the Antarctica has been of the same level."

The largest ozone hole so far was observed last year, in 1998.

Though the depleted ozone cover has not yet affected populated areas of the earths surface, sunlight does pass through the thin ozone film just for a day or two over the southern tip of South America.

"The critical zone in the lower stratosphere is between 12 to 22 kilometres," said Dr. Bojkov. "When the temperature here reaches minus 78 degrees celsius, very rapid chemical reactions are started by sunlight, destroying the protective ozone cover."

Though the magnitude, timing and regional pattern of ozone changes are now relatively well understood, there are still many uncertainties regarding the future.

First, it depends on whether all nations are likely to phase out the ozone depleting substances, CFCs and halons, by 2005, as agreed under the Montreal Protocol.

As a result of the measures by the Montreal Protocol, the increase of the concentrations of ozone depleting substances is now starting to level off, according to the WMO.

However, the effect of climate change or greenhouse gas effect has not yet been factored into the calculations so far. A continuous release of the greenhouse gases causes a cooling of the stratosphere - making the conditions for ozone depleting processes more favourable (especially valid for the Northern polar and mid-latitude springs).

"It will be practically impossible to detect unambiguously the start of the ozone recovery within the coming 20 years," says Dr. Bojkov. (SUNS4501)

The above article first appeared in the South-North Development Monitor (SUNS) .

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