By David Shukman BBC News, Punta Arenas, Chile

Twenty years ago scientists from the British Antarctic Survey (Bas) made one of the most significant environmental discoveries of recent times.

Punta Arenas lies close to Chile's southernmost tip

Studying data gathered in hostile and difficult conditions over many decades, they stumbled on the fact that a huge hole had appeared in the layer of ozone protecting the Earth from the harmful UV radiation of the Sun.

Dr Jonathan Shanklin of Bas, the scientist whose calculations produced the revelation, puts the breakthrough down to a combination of luck and diligence.

"We were in the right place at the right time with the right data," he told me.

The shock of the discovery - and its later confirmation by scientists in the US - led to prompt international action to curb the greenhouse gases known as CFCs believed to be damaging the ozone.

Most people just don't seem to understand the risks of getting cancer - the message just isn't getting through Pharmacy manager Auad Jaihatt

Although the Montreal Protocol banned CFCs, the effects of these highly stable and long-lasting gases will be felt for at least another 40 years.

Once a year, in the springtime in the Southern Hemisphere, a combination of atmospheric conditions and the CFC chemicals starts to erode the ozone layer.

From September through to November, the hole forms over a vast area above Antarctica.

Tracked by satellite, scientists can monitor its spread as it rotates with the weather systems, and occasionally stretches over the southern part of South America.

Several times a year, one of the world's southernmost cities, Punta Arenas in Chile, falls under the hole and its inhabitants suffer the worst effects of the solar radiation - including a massively raised risk of skin cancer.

Tingling skin

The city's leading skin specialist, Dr Jaime Abaca, has studied the rates of skin cancer and has concluded that of all reported cases, the worst kind, malignant melanoma, is found in three times as many people as in other parts of the world.

"There is no doubt we are seeing the effects of the ozone problem," he told me.

The ozone hole shifts around with weather patterns

Observations have also shown that the radiation that reaches the ground is on a wavelength that is particularly damaging.

Standing in the open for more than a few minutes, I could certainly feel a gentle tingling, stinging sensation on my face and others with me felt the same. Even on cloudy days we found ourselves seeking the shade of doorways and trees.

One victim is a local radio presenter, Francisco Figueredo, who has recently been treated for skin cancer on his eye, nose and cheek.

Sitting in his home as he prepared for his evening programme of jazz, he explained that back in his younger days "we knew nothing about this problem, we were completely ignorant".

Now the city is bombarded with warnings of the UV hazard. Flags of particular colours are flown at a central intersection - they were orange for "high risk" during our visit - and the radio and TV stations broadcast daily information.

'A good tan'

Yet in one large pharmacy we visited in the centre of Punta Arenas, the manageress admitted to us that sales of sun cream were never high. I asked Auad Jaihatt whether the public heeded the UV warnings.

"No, not at all. Most people just don't seem to understand the risks of getting cancer - the message just isn't getting through," she said.

There are an extraordinary number of tanning centres in the city

Most bizarre, as we drove through the streets of the city, we spotted an extraordinary number of tanning centres.

One studio, Cecilia International, has 50 customers every day. One of them, Evanalla, told me she used the sunbed three times a week.

When I asked her if she understood the risks - especially living in the city with the highest UV levels in the world - she replied that it was a matter of personal choice.

"I know all about the risks, the cancer and everything. But I feel better with a tanned skin. It is too cold here to go to the beach so this is the only chance we have."

She was adamant about a key benefit: "A good tan makes my clothes look better."