Ozone levels above Antarctica may not be recovering and changes in the southern hemisphere atmosphere may be contributing to the persistence of the ozone hole, according to a study.
In a study published in Nature Communications, New Zealand scientists analyzed the monthly and daily ozone changes at different altitudes and latitudes within the Antarctic ozone hole from 2004 to 2022.
Despite public perception, the Antarctic ozone hole has been remarkably massive and long-lived over the past four years, University of Otago researchers believe chlorofluorocarbons (CFCs), the ozone-depleting substances, are not the only things to blame.
There is much less ozone in the center of the ozone hole compared to 19 years ago, said the study's lead author Hannah Kessenich, PhD candidate in the Department of Physics, University of Otago.
"This means that the hole is not only larger in area, but also deeper throughout most of spring," Kessenich said, adding connections have been made between this drop in ozone and changes in the air that is arriving into the polar vortex above Antarctica.
This reveals the recent, large ozone holes may not be caused just by CFCs, she said, adding most major communications about the ozone layer over the last few years have given the public the impression that the "ozone issue" has been solved.
While the Montreal Protocol on Substances that Deplete the Ozone Layer, which has been in place since 1987, regulates the production and consumption of man-made chemicals known to deplete the ozone, the researchers believe other complex factors are also contributing to the ozone hole.
Currently, the 2023 ozone hole has already surpassed the size of the three years prior, and in the late last month it was over 26 million square km, nearly twice the area of Antarctica, she said.
Understanding ozone variability is important because of the major role it plays in the southern hemisphere's climate, Kessenich said, adding the Antarctic ozone hole has been part of the pictures of recent wildfires and cyclones in Australia and New Zealand, and downstream effects include changes to the southern hemisphere's wind patterns and surface climate.
"While separate from the impact of greenhouse gases on climate, the ozone hole interacts with the delicate balance in the atmosphere," she said.
She contended that as ozone usually absorbs UV light, a hole in the ozone layer can not only cause extreme UV levels on the surface of Antarctica, but it can also drastically impact where heat is stored in the atmosphere.
However, Martin Jucker, lecturer at the University of New South Wales, pointed out the ozone hole is extremely variable from year to year, and that it is only over longer terms that a trend can be identified.