New Zealand's ozone hole is shrinking for the first time in 30 years.
The depleted ozone layer - in part responsible for a 14 per cent jump in melanoma over the past decade - is healing itself, 25 years after an international ban on aerosols blamed for its rapid decline.
Research by a University of Canterbury atmospheric scientist has found that the hole is making a slow recovery, sooner than expected.
"Ozone levels above Antarctica are projected to return to 1980 levels - previous to the ozone hole - after 2050," said Dr Adrian McDonald.
He has been on the ice at Scott Base using radar to measure jetstream winds that flow from pole to pole to give an indication of the recovery.
But the research, backed by Antarctica New Zealand, has been greeted with caution by skin cancer experts.
"I'll believe it when I see it," said the interim chief executive of the Melanoma Foundation, Kylie Williams.
Melanoma killed almost one New Zealander a day and the rate increased every year, she said.
A sunscreen survey last week found only 19 per cent of Kiwis wear sunblock every day.
"The sun rays here are so fierce and if the ozone hole is depleting, we're not seeing the results yet," Mrs Williams said.
"The message remains the same: stay out of the sun, but if you're in the sun, slip, slop, slap and wrap. It's four words, but it can save your life."
The Cancer Society welcomed news of a returning ozone layer as "a great step in the right direction".
But health promotion manager Jan Pearson added: "We won't be changing our advice that people need to protect their skin against cancer."
Dr McDonald, 40, accepted it would be at least 30 years before sun worshippers could tan safely.
And he suspected solving one manmade problem may have hastened another - ozone depletion may have protected Antarctica from the worst of greenhouse gas-related warming and kept its centre cooler.
Now the hole is repairing itself, the white continent's northern latitudes have "warmed up a lot", making it one of the world's fastest-warming regions.
He was unsure about how the ozone hole's recovery would affect New Zealand's climate.
"There's potential for rapid change, but also potential for things to cancel each other out. It's an area that needs a lot more research."
Green Party climate change spokesman Kennedy Graham said Dr McDonald's research results were "reassuring".
But he warned against making comparisons between ozone depletion and the fight against climate change.
"It's like strolling in the foothills compared to climbing in the Himalayas."
What is the ozone layer?
An area of naturally occurring gas in the stratosphere, 15-35km above Earth, that protects humans and other organisms by filtering solar ultraviolet (UV) B radiation.
Why is it important for New Zealand?
Although it is present in only small amounts in the Earth's atmosphere, it is vital to human life and the ecosystem. Its decline is largely blamed for New Zealand having the highest melanoma rate in the world, with about 300 deaths a year.
What started its decline?
Chlorofluorocarbons (CFCs) - chemicals used in spray aerosols, foam, soap and refrigeration - were identified in the 1970s as causing ozone layer breakdown. The problem is particularly bad above the Antarctic where low temperatures speed up the conversion of CFCs to chlorine which reacts with UV rays and destroys the ozone.
Why has it started healing itself?
The international community banned CFCs in 1987 by signing the landmark Montreal Protocol. It is widely regarded as one of the most successful environment protection agreements in the world.