A fresh report from the UN's World Meteorological Organization highlighted that the ozone hole over the Antarctic was smaller in 2024 than in recent years, in what it said was "welcome scientific news for people's and planetary health".

"Today, the ozone layer is healing," United Nations chief Antonio Guterres said in the statement.

"This achievement reminds us that when nations heed the warnings of science, progress is possible."

The WMO said as it published its Ozone Bulletin 2024 that the declined depletion "was partially due to naturally occurring atmospheric factors which drive year-to-year fluctuations".

But, it stressed that the long-term positive trend witnessed "reflects the success of concerted international action".

The bulletin was issued to mark World Ozone Day and the 40th anniversary of the Vienna Convention, which first recognised stratospheric ozone depletion as a global problem.

That 1975 convention was followed by the Montreal Protocol, signed in 1987, which aimed to phase out ozone-depleting substances found primarily in refrigeration, air conditioning and aerosol sprays.

To date, that agreement has led to the phase-out of over 99 percent of the production and consumption of controlled ozone-depleting substances, the WMO said.

"As a result, the ozone layer is now on track to recover to 1980s levels by the middle of this century, significantly reducing risks of skin cancer, cataracts, and ecosystem damage due to excessive UV exposure," it said.

The bulletin determined that the depth of the ozone hole, which appears over the Antarctic every spring, had a maximum ozone mass deficit of 46.1 million tonnes on September 29 last year -- below the 1990-2020 average.

WMO highlighted a relatively slow onset, with delayed ozone depletion observed through the month of September, followed by a relatively rapid recovery after the maximum deficit was reached.

"This persistent later onset has been identified as a robust indication of initial recovery of the Antarctic ozone hole," the bulletin said.

The WMO and the UN Environment Programme co-sponsor a scientific assessment of ozone depletion every four years.

The most recent assessment in 2022 indicated that, if current policies remain in place, the ozone layer should recover to 1980 values -- before the hole appeared -- by around 2066 over the Antarctic, by 2045 over the Arctic, and by 2040 for the rest of the world.