The ozone layer is on track to recover in around four decades due to a global phaseout of chemicals which is also helping curb climate change, scientists said.
A UN-backed scientific assessment panel said the phaseout of nearly 99 per cent of banned ozone-depleting substances has succeeded in safeguarding the ozone layer, which is recovering in the upper stratosphere.
The Montreal Protocol came into force in 1989, after scientists raised the alarm over a “hole” or decrease in the Earth’s ozone layer which protects humans against harmful ultraviolet rays. The international agreement bans ozone-depleting chemicals such as CFCs, and the latest four-yearly report from the scientific assessment panel to the Montreal Protocol assesses its impact.
If current policies remain in place, the ozone layer is expected to recover to 1980 levels – before the appearance of the hole – by around 2066 over the Antarctic, by 2045 over the Arctic, and by 2040 for the rest of the world.
Variations in the size of the Antarctic ozone hole, particularly between 2019 and 2021, were driven largely by meteorological conditions, but the hole has been slowly improving in area and depth since 2000, the report said.
The assessment says that action under the Montreal Protocol is also having a beneficial impact on efforts to curb global warming, but it warned that “geoengineering” the stratosphere to limit rising temperatures could have unintended consequences.
An update to the Montreal Protocol in 2016, known as the Kigali amendment, saw countries agree to phase down the production and consumption of some hydrofluorocarbons or HFCs. These do not directly deplete ozone but, similar to long-lived CFCs, they can have a powerful global warming effect.
The new assessment said the Kigali amendment is estimated to avoid between 0.3 degrees and 0.5 degrees of global warming by 2100.
It also says new studies support previous assessments that the decline in emissions of ozone-depleting substances due to the Montreal Protocol avoids an additional global warming of around 0.5 degrees 1 degree by mid-century, compared with “an extreme scenario” of increases in the chemicals of up to 3.5 per cent a year.
Meg Seki, executive secretary of the United Nations Environment Programme’s ozone secretariat, said: “That ozone recovery is on track according to the latest quadrennial report is fantastic news.
“The impact the Montreal Protocol has had on climate change mitigation cannot be overstressed. Over the last 35 years, the protocol has become a true champion for the environment.”
World Meteorological Organisation secretary general Professor Petteri Taalas said: “Ozone action sets a precedent for climate action.
“Our success in phasing out ozone-eating chemicals shows us what can and must be done – as a matter of urgency – to transition away from fossil fuels, reduce greenhouse gases and so limit temperature increase.”
The panel also examined the potential effects of a form of geoengineering – large-scale intervention in natural systems to counteract climate change – on the ozone layer.
They looked at the proposed deliberate addition of aerosols into the stratosphere – known as stratospheric aerosol injection – to reflect more sunlight and reduce warming.
The panel cautions that the unintended consequences of this process could also affect stratospheric temperatures, circulation and ozone production and destruction rates and movement.