The hole in the ozone layer over Antarctica appears to be healing, say scientists.
Recovery of the hole has varied from year to year, partly because of the effects of volcanic eruptions.
Now after taking account of volcanic influence, scientists have concluded that the ozone layer really is on the mend.
They predict that the hole could close permanently by the middle of the century.
The change is attributed to the 1987 Montreal Protocol, which brought in a ban on the use of ozone-destroying chlorofluorocarbons (CFCs).
At the time, the chemicals were widely used in refrigerators and aerosol cans.
Dr Ryan Neely, a member of the international team from the University of Leeds, said: “Observations and computer models agree; healing of the Antarctic ozone (layer) has begun.”
The findings, published in the journal Science, show that the average September size of the ozone hole has shrunk by more than 1.7 million square miles (4.4 million sq km) since 2000.
That is a patch of the sky roughly 18 times the area of the UK.
The ozone hole does not remain static but grows from August each year, reaching its peak size in October.
For the new study the scientists tracked the yearly opening of the hole each September from 2000 to 2015.
Choosing September instead of October provided a clearer picture of the effects of chlorine. At that time of year, chlorine chemistry is firmly in control of the rate at which the hole forms.
The ozone layer is important because it acts as a natural sun block, absorbing harmful ultraviolet (UV) radiation from the sun.
Without ozone in the atmosphere plants and the animals that depend on them could not survive on Earth.