The Earth's protective ozone layer is well on track to recovery in the next few decades, thanks to concerted international action against ozone depleting substances, said a UN report Wednesday.
The conclusion was made in the assessment published Wednesday by the United Nations Environment Programme (UNEP) and the World Meteorological Organisation (WMO), Xinhua reported.
The Assessment for Decision-Makers, a summary document of the Scientific Assessment of Ozone Depletion 2014, said actions taken under the Montreal Protocol on Substances that Deplete the Ozone Layer, signed Sep 16, 1987, to protect the ozone layer by phasing out the production of numerous substances that are responsible for ozone depletion, are enabling the return of the ozone layer to benchmark 1980 levels.
It said the Montreal Protocol and associated agreements have led to decreases in the atmospheric abundance of gases, such as CFCs (chlorofluorocarbons) and halons, once used in products such as refrigerators, spray cans, insulation foam and fire suppression.
In 1987, ozone-depleting substances contributed about 10 gigatonnes CO2-equivalent emissions per year. The Montreal Protocol has now reduced these emissions by more than 90 percent.
Under full compliance with the Montreal Protocol, the ozone layer is expected to recover to 1980 benchmark levels, the time before significant ozone layer depletion, before the middle of the century in mid-latitudes and the Arctic, and somewhat later in the Antarctic.
However, the assessment warned the climate benefits of the Montreal Protocol could be significantly offset by projected emissions of HFCs (hydrofluorocarbons) used to replace ozone depleting substances.
Hydrofluorocarbons (HFCs) do not harm the ozone layer but many of them are potent greenhouse gases. They currently contribute about 0.5 gigatonnes of CO2-equivalent emissions per year.
These emissions are growing at a rate of about 7 percent per year. Left unabated, they can be expected to contribute significantly to climate change in the next decades.
Meanwhile, the assessment said the ozone layer in the second half of the 21st century will largely depend on concentrations of CO2, methane and nitrous oxide, the three main long-lived greenhouse gases in the atmosphere.
Overall, CO2 and methane tend to increase global ozone levels. By contrast, nitrous oxide, a by-product of food production, is both a powerful greenhouse gas and an ozone depleting gas, and is likely to become more important in future ozone depletion.
"This latest assessment provides solid science to policy-makers about the intricate relationship between ozone and climate and the need for mutually-supportive measures to protect life on earth for future generations," WMO Secretary General Michel Jarraud said in a statement.
"International action on the ozone layer is a major environmental success story, this should encourage us to display the same level of urgency and unity to tackle the even greater challenge of climate change," he added.
The Scientific Assessment of Ozone Depletion 2014, which is the first comprehensive update in four years, will be presented at the annual meeting of the parties to the Montreal Protocol, to be held in Paris in November 2014. The full body of the report will be issued in early 2015.
