The annual springtime ozone hole over Antarctica peaked in early October, covering 25 million square kilometres, more than three times the area of Australia.

Graph: shows how ozone levels over Antarctica have declined since the 1960s is available on request. Animations showing development of the ozone hole and ozone destruction are also available.

Measurements at Halley Bay in Antarctica reveal that October ozone concentrations are now less than half what they were during the 1960s.

Ozone damage has not been restricted to Antarctica. The ozone layer over sub-tropical parts of Australia has thinned, which means that levels of harmful ultraviolet radiation reaching the ground are far greater than in the past.

Signatories to the Montreal Protocol to protect the ozone layer are meeting this week in Beijing to discuss funding to help developing countries eliminate ozone-depleting chemicals.

"A measure of the seriousness of ozone depletion is the fact that the amount of DNA damaging radiation measured in New Zealand under cloudless skies has risen by over 30 per cent during the past 20 years," says Dr Fraser.

DNA damaging radiation is ultraviolet radiation that is most likely responsible for skin cancer. Ultraviolet radiation is greatest on cloudless days.

Anticipated global warming next century will cool the stratosphere, further increasing the rate of ozone destruction, according to Dr Fraser.

"Based on the maximum predicted emissions of ozone depleting chemicals allowed under the Montreal Protocol, it will be at least the year 2050 before the ozone layer recovers. Global warming may further delay recovery by 10-20 years," says Dr Fraser.

"A positive step we could take to reduce emissions would be to expand chlorofluorocarbon (CFC) and halon recovery, recycling or destruction," he says.

In Australia, the not-for-profit companies Refrigerant Reclaim and the Halon Bank are responsible for CFC and halon recovery, recycling and destruction.

The ozone layer is part of the earth's stratosphere, 15 to 30 kilometres above our planet's surface. Chlorine and bromine atoms released from CFCs and halons respectively, cause the depletion of the ozone. CFCs are industrial chemicals used in the past as refrigerants, solvents, pressure packs and foaming agents. Halons were used as fire fighting chemicals.

Australia and other developed countries have completely phased out production of CFCs and halons. Under the Montreal Protocol, designed to protect the ozone layer, developing countries have until the year 2010 before they must completely phase out halon production.

Support for CSIRO's research into ozone depletion comes from the Co-operative Research Centre for Meteorology at Monash University, and from Refrigerant Reclaim Australia.