SYDNEY, Australia -- Chlorine-based chemical levels in the atmosphere are falling, and the hole in the ozone layer over Antarctica should close within 50 years, according to an Australian government-funded study.

Although the ozone layer had not yet begun to repair itself, the hole would probably start closing within five years, and should fully recover by 2050, said Paul Fraser, of the Australian government-funded Commonwealth Scientific and Industrial Research Organization, or CSIRO.

Fraser said ozone layer recovery would be a result of international efforts to ban ozone-depleting chlorofluorocarbons in the mid-1990s.

CSIRO atmospheric monitoring has found that chlorine from chlorofluorocarbons, or CFCs, leveled off in the troposphere -- the lower atmosphere -- two years ago, and is falling for the first time in more than 20 years.

The ozone layer over the southern continent of Antarctica has suffered the most damage from CFCs, which have eaten a hole about 10 million square miles. The hole is about three times the size of Australia.

The ozone recovery will not alleviate projected global warming problems, however, which is related to the release of other heat-trapping gases into the atmosphere.

New Zealand ozone researcher Greg Bodecker, when asked about the Australian findings Wednesday, said measurements from a number of sites around the world, by several research groups, "have confirmed that stratospheric chlorine levels have indeed peaked."

Measurements at one site in New Zealand have confirmed that stratospheric chlorine levels "are probably now decreasing," Bodecker said.

CFCs were banned in the developed world in the mid-1990s after a pact signed at a 1989 international conference in Montreal, Canada. They are still being phased out in developing countries.

The prohibition of CFCs -- which were used in refrigerators, air conditioners and aerosol spray cans -- came after it was found they were breaking up the earth's ozone, a thin layer of atmosphere that filters the sun's damaging ultraviolet rays and protects humans from skin cancer.

"Once CFCs have been phased out of the developing world ... by about 2005, the most persistent ozone-depleting chemicals in the atmosphere will no longer be released in any significant amounts," Fraser told The Associated Press in a telephone interview on Tuesday.

"That means that the atmosphere can work its magic and start to destroy these chemicals at a rate faster than they're being released," he added.

Fraser said the discovery proved that direct action taken by the international community on environmental issues could make a difference.

On Monday, the U.N. Environmental Program and World Meteorological Organization said the ozone layer remains at risk despite signs of recovery.

Also Monday, scientists meeting in Utah said it would take 50 years for the hole in the ozone layer to disappear.

The "world is making steady progress toward the recovery of the ozone layer ... with the total amount of ozone-depleting chemicals in the lower atmosphere continuing to decline, albeit slowly," the organizations said in a statement.