Earth's protective ozone layer is well on track to recovery in the next few decades, owing largely to the phase-out of certain chemicals used in refrigerants and aerosol cans, according to a new UN report.
The conclusion was made in the assessment published by the United Nations Environment Programme (UNEP) and the World Meteorological Organisation (WMO).
The stratospheric ozone layer, a fragile shield of gas, protects Earth from harmful ultraviolet rays of the sun. Without the Montreal Protocol and associated agreements, atmospheric levels of ozone depleting substances could have increased tenfold by 2050, according to a summary document of the Scientific Assessment of Ozone Depletion 2014.
The Protocol will have prevented 2 million cases of skin cancer annually by 2030, averted damage to human eyes and immune systems, and protected wildlife and agriculture, according to UNEP.
The phase-out of ozone depleting substances has had a positive spin-off for the global climate because many of these substances are also potent greenhouse gases.
"There are positive indications that the ozone layer is on track to recovery towards the middle of the century. The Montreal Protocol - one of the world's most successful environmental treaties - has protected the stratospheric ozone layer and avoided enhanced UV radiation reaching the earth's surface," said UN Under-Secretary-General and UNEP Executive Director Achim Steiner.
"International action on the ozone layer is a major environmental success story," said WMO Secretary-General Michel Jarraud.
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, the report 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.
Total column ozone declined over most of the globe during the 1980s and early 1990s. It has remained relatively unchanged since 2000, but there are recent indications of its future recovery, the report said.
The Antarctic ozone hole continues to occur each spring and it is expected to continue occurring for the better part of this century given that ozone depleting substances persist in the atmosphere, even though their emissions have ceased.
The Arctic stratosphere in winter/spring 2011 was particularly cold, which led to large ozone depletion as expected under these conditions, according to the report.
However, the report found the climate benefits of the Montreal Protocol could be significantly offset by projected emissions of HFCs (hydrofluorocarbons) used to replace ozone depleting substances.
