It was back in the mid-1980s that the British Antarctic Survey discovered the level of ozone, which shields life on Earth from the sun’s harmful ultraviolet rays, was dropping.
The discovery of the hole led to a worldwide effort to attempt to stop the damage and the 1987 Montreal Protocol, which heralded a ban on the use of chlorofluorocarbons (CFCs) – then widely used in cooling appliances and aerosol cans.
Now, scientists from the University of Leeds, part of an international team led by Professor Susan Solomon of the Massachusetts Institute of Technology, have confirmed the first signs of healing in the ozone layer.
Recovery of the hole has varied from year to year, due in part to the effects of volcanic eruptions.
But accounting for the effects of these eruptions allowed the team to show that the ozone hole is healing, and they see no reason why the ozone hole should not close permanently by the middle of this century.
The findings, published in the journal Science, show the average size the ozone hole each September has shrunk by more than 1.7m square miles since 2000 – roughly 18 times the area of the United Kingdom.
Co-author of the report, Dr Ryan R Neely III, a lecturer in observational atmospheric science at Leeds, said: “Observations and computer models agree; healing of the Antarctic ozone has begun.
“We were also able to quantify the separate impacts of man-made pollutants, changes in temperature and winds, and volcanoes, on the size and magnitude of the Antarctic ozone hole.”
His colleague and fellow co-author Dr Anja Schmidt, an academic research fellow in volcanic impacts, said: “The Montreal Protocol is a true success story that provided a solution to a global environmental issue.”
She added that the team’s research had shed new light on the part played by recent volcanic eruptions – such as at Calbuco in Chile in 2015 – in ozone depletion.
“Despite the ozone layer recovering, there was a very large ozone hole in 2015,” she said. “We were able to show that some recent, rather small volcanic eruptions slightly delayed the recovery of the ozone layer.
“That is because such eruptions are a sporadic source of tiny airborne particles that provide the necessary chemical conditions for the chlorine from CFCs introduced to the atmosphere to react efficiently with ozone in the atmosphere above Antarctica. Thus, volcanic injections of particles cause greater than usual ozone depletion.”
The ozone hole begins growing each year when the sun returns to the South Polar cap from August, and reaches its peak in October – traditionally the main focus for research. The scientists believed they would get a clearer picture of the effects of chlorine by looking earlier in the year in September, when cold winter temperatures still prevail and the ozone hole is opening up. The team showed that as chlorine levels have decreased, the rate at which the hole opens up in September has slowed down.
Professor Solomon said: “We can now be confident that the things we’ve done have put the planet on a path to heal. We decided collectively, as a world, ‘Let’s get rid of these molecules’.
“We got rid of them, and now we’re seeing the planet respond.”