The hole in the protective ozone layer over the Antarctic is forming again but should remain just below the record size it reached last year, a scientist at the UN's weather agency said Wednesday.

The gap in the ozone in the upper atmosphere, at altitudes of up to 25 kilometres (15 miles), has reached a size of about 23 million square kilometres (8.9 million square miles), said World Meteorological Organisation ozone expert Geir Braathen.


In 2006, the hole covered an area of 29.5 million square kilometres (11.39 million square miles), exceeding the previous record set six years earlier.

"This year, the temperature in the stratosphere is a little less cold than in 2006. It's therefore possible that the hole might be a little smaller," Braathen told AFP.

Stratospheric ozone provides a natural protective filter against harmful ultra violet rays from the sun, which can cause sunburn, cataracts, skin cancers and damage vegetation.

Its depletion is caused by extreme cold temperatures at high altitude and a particular type of pollution, from chemicals often used in refrigeration, some plastic foams, or aerosol sprays, which have accumulated in the atmosphere.

Most of the chemicals, chloroflurocarbons (CFC), are being phased out under the 1987 Montreal Protocol, but they linger in the atmosphere for many years.

The hole in the layer over the Antarctic was discovered in the 1980s. It regularly tends to form in August before it fills again in mid-December.

Countries taking part in the Montreal Protocol are expected to have tough discussions next week about phasing out another class of ozone-harming chemical, HCFCs, which are used as refrigerants in some air conditioning units, Braathen said.

The meeting in Montreal, Canada, will follow World Ozone Day on September 16, marking 20 years since the treaty was signed.