Ellen Phiddian
Cosmos science journalist
Despite a slump caused by a large volcanic eruption, the ozone layer is still improving in the long term, according to an annual global report.
The United Nations’ World Meteorological Organization (WMO) has published its Ozone and UV Bulletin, finding that the ozone layer remains on track to recover fully between the 2040s and the 2060s.
The bulletin finds that levels of chlorine and bromine have continued to drop in the troposphere, suggesting that ozone-depleting substances are declining.
These substances (chlorofluorocarbons or CFCs), which were banned by the 1987 Montreal Protocol, also have a warming effect, meaning their decline is also good news for climate change.
“The ozone layer, once an ailing patient, is on the road to recovery,” said UN Secretary-General António Guterres in a statement.
“At a time when multilateralism is under severe strain, the Montreal Protocol to help protect the ozone layer stands out as a powerful symbol of hope.”
The ozone layer fluctuates annually, with the hole over Antarctica reaching its largest extent in September and October each year.
In 2023, the hole was unusually large and long-lasting, beginning in August and lasting until December.
While atmospheric researchers are still studying this dip, the bulletin suggests that the eruption of Hunga Tonga-Hunga Ha’apai volcano in January 2022 played a large role.
This colossal explosion ejected a huge amount of water vapour into the atmosphere, which depleted ozone in the upper layers of the stratosphere, and had a cooling effect which also depletes ozone.
The WMO says in its bulletin that while this finding highlights “there are relatively rare atmospheric events that can have a significant impact on the Antarctic ozone hole”, the results still “do not challenge” their findings that the layer is recovering in the long term.
The bulletin also points out that 2023 ozone levels were higher than usual in the mid-latitudes of the Southern Hemisphere.
Ozone in this region was depleted over the last couple of years, due in part to the 2019-20 Black Summer bushfires which sent a large amount of smoke into the atmosphere. The smoke produced atmospheric reactions which researchers believe depleted the ozone layer.
But the high 2023 levels suggest that depletion is at an end.
Based on current policies, the WMO expects the ozone layer to return to 1980 levels by 2066 over Antarctica, by 2045 over the Arctic, and by 2040 for the rest of the world.
“Now, it’s time to go further,” said Guterres, emphasising the importance of the Kigali Agreement, a 2016 amendment to the Montreal Protocol which aims to reduce hydrofluorocarbons, which warm the climate as well as depleting ozone.
“If fully ratified and implemented, the Kigali Amendment could help avoid as much as 0.5 degrees Celsius of global heating by the end of this century,” said Guterres.
The bulletin emphasises the importance of continuing to monitor ozone and ozone-depleting substances, so that scientists can understand what threatens and helps it.
