A study reveals that the ozone hole above Antarctica has been expanding each austral spring for about two decades, despite the ban on chemicals responsible for its depletion.
The stratospheric ozone layer, vital for shielding the Earth from harmful solar radiation, extends between 11 and 40 km above the Earth’s surface. It filters out the sun’s ultraviolet rays that can cause cancer, compromise the immune system, and damage living organisms’ DNA.
In the mid-1970s, chlorofluorocarbons (CFCs), once widely used in aerosols and refrigerators, were identified as the primary culprits behind ozone layer depletion, leading to yearly “holes,” notably a large one above Antarctica. In response, the Montreal Protocol was enacted in 1987, banning CFCs to eliminate these holes—a successful global environmental cooperation initiative.
Despite a decrease in CFC use, the ozone hole above Antarctica has not significantly shrunk, as indicated by a study published on Tuesday in Nature Communications. Six of the last nine years have witnessed very low ozone levels and extremely large ozone holes, challenging the expected recovery.
Annika Seppala from the University of Otago in New Zealand, a co-author of the study, suggests that factors beyond reduced CFC use may be at play, potentially linked to climate change, obscuring part of the recovery.
The Antarctic ozone hole typically forms from September to November during the southern spring, gradually closing afterward. Unusual late openings in September hint at a potential recovery due to reduced CFCs. However, between 2004 and 2022, ozone levels in the mid-stratospheric layer decreased by 26% during the peak size of the hole in October, based on satellite data.
While CFC reduction remains on track per the Montreal Protocol, the study indicates that recent large ozone holes may not be solely attributed to these substances. Unusual environmental events in recent years, such as the significant wildfires in Australia in 2020 and the eruption of the Hunga-Tonga-Hunga-Ha’apai underwater volcano in the Pacific Ocean in January 2022, have likely influenced stratospheric ozone levels.