GENEVA - The ozone layer that shields life from the sun's harmful rays is projected to largely recover from harmful chemicals by mid-century, but it will take longer over the polar regions, a United Nations study said on Thursday.
Ozone depletion will continue for many more decades because several key damaging substances endure in the atmosphere for a long time after emissions end, it said.
"Over the past decade, global ozone and ozone in the Arctic and Antarctic regions is no longer decreasing but it is not yet increasing," said the report by the World Meteorological Organization (WMO) and the U.N. Environment Programme (UNEP).
While chemicals such as chlorofluorocarbons (CFCs), once used in refrigerators and other appliances, have been phased out, demand for replacements such as hydrofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) has increased. Many are also potent greenhouse gases, blamed for causing global warming.
The report by 300 scientists credited the 1987 Montreal Protocol signed by some 200 countries with stopping additional ozone loss and helping to mitigate the greenhouse effect.
"It has protected the stratospheric ozone layer from much higher levels of depletion by phasing out production and consumption of ozone depleting substances," a statement said.
"As a result of the phase-out of ozone depleting substances under the Montreal Protocol, the ozone layer outside the polar regions is projected to recover to its pre-1980 levels some time before the middle of this century."
However, the ozone hole which forms over the Antarctic every springtime is only expected to return to the pre-1980 benchmark values "in the late 21st century", the report said.
High levels of ultraviolet rays continue to be detected in Antarctica when the springtime ozone hole is large, it added.
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