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This is the VOA Special English ENVIRONMENT REPORT.

Australian researchers say the hole in the ozone layer over Antarctica probably would start closing within five years. They say it may be completely closed within fifty years. The ozone layer protects the Earth from dangerous radiation from the sun. The hole in the ozone layer was discovered over Antarctica almost thirty years ago. At the time, it was three times the size of Australia.

Paul Fraser is chief researcher of the Commonwealth Scientific and Industrial Research Organization in Australia. Mister Fraser led a study about the ozone layer for the United Nations and the World Meteorological Organization.

The report found that ozone-destroying gases in the upper atmosphere had been at or near their highest levels in the year two-thousand. But since then, there has been continued progress toward recovery of the ozone layer. Satellite information showed levels of ozone-destroying gases in the atmosphere are slowly decreasing.

Chlorine from chlorofluorocarbons, or C-F-C's, is responsible for destroying part of the ozone layer over Antarctica. C-F-C's have been widely used since the nineteen-thirties in cooling devices such as refrigerators and air conditioners. C-F-C's remain in the atmosphere for years.

Government scientists say the level of chlorine in the atmosphere is decreasing because of restrictions on the use of chlorofluorocarbons. The chemicals were restricted under an international agreement called the Montreal Protocol in nineteen-eighty-seven.

Under the Montreal agreement, developing countries promised to cut their use of chlorofluorocarbons in half by the year two-thousand-five. They also agreed to an eighty-five percent cut by the year two-thousand-seven.

The ozone hole forms over Antarctica in August and September, when the temperatures are coldest. Thin clouds form in these cold conditions. Chemical reactions on the cloud particles help chlorine-based chemicals to rapidly destroy ozone. By early October, temperatures begin to warm and the ozone layer begins to recover.

At its largest this year, the ozone hole covered more than fifteen-million square kilometers. That is down from an average of twenty-three-million square kilometers over the last six years.

This VOA Special English ENVIRONMENT REPORT was written by Cynthia Kirk.