Human-induced ozone depletion, which once threatened massive disruption to life on Earth, is lessening on a global scale, the European Space Agency said yesterday.

"We found a global slightly positive trend of ozone increase of almost 1 per cent per decade in total ozone from the last 14 years," said Diego Loyola, of the German Aerospace Centre.

Their finding comes as this year's Antarctic ozone hole appears likely to level out below the worst 2006 benchmark, confirming predictions that repair is likely, though distant.

Destruction of the atmosphere's ozone layer in the 20th century was caused by the release of household chemicals, mainly chlorofluorocarbons.

Ozone loss increased the risk of skin cancer, cataracts and harm to marine life from the Sun's ultraviolet rays. The damage, highlighted by the Antarctic hole, was discovered in the early 1980s and governments agreed to ban the chemicals in the 1987 Montreal Protocol.

"The Montreal Protocol was absolutely critical," said Roger Dargaville, research fellow in Climate Change at Melbourne University. "It is to this day the world's most successful treaty, with every country on Earth signing on."

Upper atmosphere air circulation sent most ozone-depleting gases to the poles, particularly Antarctica, where they reached a maximum concentration about the year 2000, the World Meteorological Organisation says.

The hole reached a maximum of 27.4 million square kilometres on September 24, 2006, and this year by mid-September had reached an area of up to 25 million square kilometres, the WMO said.

Dr Dargaville said it was too early to see a statistical trend in the size of the Antarctic hole, though there was every expectation that in the next 50 years or so, it would repair.

He said the negotiation of the Montreal Protocol offered a useful precedent for governments struggling with climate change talks leading up to the UN conference in Copenhagen later this year.

"As now, the scientific evidence was presented, and it was vigorously debated," Dr Dargaville said. "The consensus was that the science was robust and it had to be done.

"The difference was it was a relatively simple problem to replace CFCs with other chemicals. In the global warming problem, we don't have an easy alternative to fossil fuels."