Ozone in parts of the stratosphere has recovered at a rate of one to three per cent since 2000 and, at projected rates, Northern Hemisphere and mid-latitude ozone is scheduled to heal completely by the 2030s, followed by the Southern Hemisphere in the 2050s and polar regions by 2060.
Paul Newman, chief Earth scientist at Nasa's Goddard Space Flight Center, described the discovery as "really good news".
The Protocol was in response to the revelation that chlorofluorocarbons (CFCs) and other ozone-depleting substances - used in aerosols, cooling and refrigeration systems, and many other items - were tearing a hole in the ozone layer and allowing unsafe ultraviolet radiation to flood through.
The four-yearly review of the Montreal Protocol, a global agreement which was implemented to protect the stratospheric ozone layer by phasing out the production and consumption of ozone-depleting substances, found long-term decreases in the atmospheric abundance of controlled ozone-depleting substances and the ongoing recovery of stratospheric ozone. Use of man-made chemicals called chlorofluorocarbons (CFCs), which release chlorine and bromine, began eating away at the ozone.
This year, the ozone hole over the South Pole peaked at almost 9.6 million square miles - which is still about 16% smaller than the biggest hole recorded.
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But the report, from the UN's environment and world meteorological organisation, said there is evidence of an unexpected increase in CFC-11 from eastern Asia since 2012. The worldwide agreement compelled the global community to begin the phasing out of ozone-depleting substances like chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and halons.
A United Nations study has shown that the ozone layer is recovering at a rate of one to three per cent per decade. He noted that if nothing had been done, two-thirds of the ozone layer would have been destroyed by 2065.
"We are only at a point where recovery may have started", Toon said, pointing to some ozone measurements that haven't increased yet.
And the replacements now being used to cool cars and refrigerators need to be replaced themselves with chemicals that don't worsen global warming, Newman said.
This healing progress is attributed to worldwide initiatives under the Montreal Protocol, a global agreement that was formed more than 30 years ago in response to climate change concerns.
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"I don't think we can do a victory lap until 2060", Newman told AP.
The stratosphere increases in warmth with elevation because ozone gases in the upper layers absorb intense ultraviolet radiation from the sun.
Ozone is only a trace gas in the atmosphere - about 3 molecules for every 10 million molecules of air.
The ozone layer absorbs about 98% of harmful cancer-causing UV light - so it is vitally important.
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