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ENVIRONMENT REPORT - Shrinking Ozone Hole over Antarctica
By Cynthia Kirk
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. Mr 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 year2000. 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-Cs,
is responsible for destroying part of the ozone layer over Antarctica.
C-F-Cs have been widely used since the nineteen-thirties in cooling
devices such as refrigerators and air conditioners. C-F-Cs 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 1987.
Under the Montreal agreement, developing countries
promised to cut their use of chlorofluorocarbons in half by the year
2005. They also agreed to an 85% 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.
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