The hole in the ozone layer over Antarctica has grown every Australian spring for the past twenty years, despite a ban on chemicals that destroy the shield that protects the Earth from dangerous solar radiation, according to a study published on Tuesday, AFP and Agerpres reported.

The stratospheric ozone layer, located between 11 and 40 kilometers above the Earth’s crust, filters the sun’s ultraviolet radiation, which can cause cancer, alter the immune system, and even affect the DNA of living things.

In the mid-1970s, chlorofluorocarbons (CFCs), widely used in the manufacture of aerosols and refrigerants, were recognized as the main culprits in the depletion of the ozone layer, creating “holes” every year, including a particularly large one over Antarctica.

The Montreal Protocol of 1987, which banned CFCs to promote the elimination of holes in the ozone layer, is considered a success of global environmental cooperation.

The new research follows upbeat news earlier in the year

In January 2023, UN-authorized experts recognized the agreement as effective: according to their forecasts, the ozone layer should recover by about 2066 in the Antarctic, by 2045 over the Arctic and by 2040 in the rest of the world.

But despite the reduction of freon, the hole over Antarctica has not yet decreased significantly, according to the authors of the study published in the journal Nature Communications.

“Six of the last nine years have been marked by very low ozone levels and extremely large ozone holes,” Annika Seppala of the Department of Physics at the University of Otago in New Zealand, co-author of the study, told AFP.

“Maybe there’s something else going on in the atmosphere — maybe because of climate change — and that’s masking some of the recovery,” she added.

The hole in the ozone layer over Antarctica usually opens in September and lasts until November, during the Southern Hemisphere spring, before gradually closing.

Holes in the ozone layer can have other causes

According to scientists, the ozone hole opened up later in September, a sign of recovery that can no doubt be attributed to the reduction of CFCs. But in October, when the hole reaches its maximum size, ozone levels in the mid-stratospheric layer have fallen by 26% between 2004 and 2022, according to research based on satellite data.

The reduction of the amount of freons in the atmosphere, provided for by the Montreal Protocol, however, remains “on the plan”, emphasizes Hanna Kessenich, the lead author of the new study. But “our findings show that these large newly formed holes are caused by more than just these substances.”

For Susan Solomon, a well-known ozone expert who was not involved in the new study, the results of this study should be interpreted in light of the fact that “the last few years have been quite unusual,” she told AFP.

This specialist chemist has previously revealed that the hole in the ozone layer has increased by 10% in 2020 due to the massive bushfires in Australia. The giant eruption of the Hunga Tonga Haapai submarine volcano in the Pacific Ocean in January 2022 also reduced stratospheric ozone levels, according to a recent study published in the journal PNAS.