THE restoration of the ozone layer – which lies miles away from Earth and protects the planet from ultraviolet radiation – has been celebrated as one of the world’s greatest environmental successes. But in According to a new study published Tuesday, some scientists say it may not have recovered at all and that the hole may even be expanding.
The findings are at odds with widely accepted assessments of the state of the ozone layer, including a recent United Nations-backed study that showed it will return to 1980s levels as early as 2040.
In 1987, several countries agreed to ban or phase out the use of more than 100 ozone-depleting chemicals that had caused a “hole” in the layer above Antarctica. The depletion is primarily attributed to the use of chlorofluorocarbons, or CFCs, common in aerosol sprays, solvents and refrigerants.
This ban, agreed under the Montreal Protocol, is widely considered effective in helping to restore the ozone layer.
But the hole, which grows over Antarctica during the spring before shrinking again in the summer, reached a record size between 2020 and 2022, prompting New Zealand scientists to investigate why.
In a paper, published by Nature Communications, they found that ozone levels have reduced by 26 percent since 2004 at the center of the hole in the Antarctic Spring.
“This means that the hole not only remained large in terms of area, but also became deeper [i.e. has less ozone] during much of the Antarctic spring,” said Hannah Kessenich, a PhD candidate at the University of Otago and lead author of the study.
“Particularly long-lived ozone holes in 2020-2022 fit this picture perfectly, as the size/depth of the hole in October was particularly notable in all three years.”
To reach this conclusion, scientists analyzed the behavior of the ozone layer from September to November using a satellite instrument. They used historical data to compare this behavior and changing ozone levels and to measure signs of ozone recovery. They then tried to identify what was driving these changes.
They found that the ozone depletion and deepening of the hole were the result of changes in the Antarctic polar vortex, a vast vortex of low pressure and very cold air, high above the South Pole.
The study authors went no further in exploring the causes of such changes, but acknowledged that many factors could also contribute to ozone depletion, including planet-warming pollution; tiny particles suspended in the air emitted by wildfires and volcanoes; and changes in the solar cycle.
“Overall, our findings reveal that recent large ozone holes may not be caused by CFCs alone,” Kessenich said. “So, while the Montreal Protocol has been unquestionably successful in reducing CFCs over time and preventing environmental catastrophe, recent persistent ozone holes in the Antarctic appear to be closely linked to changes in atmospheric dynamics.”
Some scientists are skeptical of the results of the study, which relies heavily on holes observed in 2020-2022 and uses a short period – 19 years – to draw conclusions about the long-term health of the ozone layer.
“Existing literature has already found reasons for these large ozone holes: smoke from the 2019 forest fires and a volcanic eruption (La Soufriere), as well as a general relationship between the polar stratosphere and the El Niño Southern Oscillation ”said Martin Jucker, a scientist at the University of Washington. The Climate Change Research Center at the University of New South Wales in Australia told the Science Media Center.
“We know that during La Niña years, the polar vortex in the stratosphere tends to be stronger and colder than usual, which means that ozone concentrations will also be lower during those years. The years 2020-22 saw a rare triple La Niña, but this relationship is never mentioned in the study.”
It adds that the study authors said they removed two years from the data – 2002 and 2019 – to ensure that “exceptional events” did not skew their findings.
“Such events have been shown to have strongly reduced the size of the ozone hole,” he said, “so including them would likely have negated any long-term negative trends.”