One Question Quiz
It’s time to let go of one of our favourite grievances. (Image: Tina Tiller)
It’s time to let go of one of our favourite grievances. (Image: Tina Tiller)

ScienceMarch 19, 2024

Antarctica’s ozone hole causes our high skin cancer rates, right? Wrong.

It’s time to let go of one of our favourite grievances. (Image: Tina Tiller)
It’s time to let go of one of our favourite grievances. (Image: Tina Tiller)

Why does this myth persist, and what’s the real reason our skin is suffering?

It’s one of the biggest international grievances New Zealanders hold, up there with the sinking of the Rainbow Warrior and 1981’s underarm incident. We’re quick to tell international travellers that the world’s pollution led to the formation of an ozone hole above us which makes our sun fiercer than anywhere else. 

We’re not the only ones. Wander over to Reddit and you’ll find multiple threads of people concerned about travelling or moving to New Zealand because it’s “under an ozone layer hole”.

And yet the popular notion that the ozone hole is the reason we have the world’s highest skin cancer rates – and why the sunburned British traveller is a fixture of our summers – is a myth.

So why does this myth persist, and what’s the real reason for our dismal skin cancer rates?

First, a brief explainer. The ozone layer is a diffuse accumulation of ozone molecules between 15 and 30km above the earth’s surface. Fortunately, it absorbs about 90% of the cancer-causing UVB radiation from the sun. Without this layer, the planet would essentially be irradiated, making it almost unlivable. 

But inadvertently, humans invented a molecule that destroys it. In the 1970s, scientists discovered that synthetic molecules called chlorofluorocarbons (CFCs), used in aerosol cans and refrigerators, were reacting with the ozone layer, causing it to slowly break down. Despite the threat of irradiating the globe, progress to curb CFC use was sluggish and CFC producers fought reductions at every step. 

NIWA emeritus researcher Richard McKenzie says the ozone hole saga is a case of crisis averted. (Photo supplied)

Then in 1985, there was an alarming new discovery. Satellites found the ozone above Antarctica was thinning at an alarming rate, with an area of about 20 million square kilometres thinning by up to a third each spring. And this “hole” was increasing in size each year. 

For New Zealand, with the largest population close to Antartica, there was a real fear the hole would continue to expand, leading to a huge spike in UV radiation here and a future tsunami of skin cancers.

Fortunately, the discovery galvanised global action and countries signed the Montreal Protocol in 1987 to phase out CFCs. It was enormously successful, and CFC production plummeted. But because the gases are extremely long-lived, those released over preceding decades continued to react with the ozone layer, and Antartica’s ozone hole continued to grow before peaking in 2006.

Given the very real threat that the ozone hole posed to New Zealand, it’s not surprising it’s become embedded in the popular consciousness. However, NIWA emeritus researcher Richard McKenzie says the ozone hole saga is one of crisis averted, rather than an ongoing catastrophe. 

“It’s been a success story,” McKenzie says. “Because of the success of the Montreal Protocol those worst-case scenarios didn’t eventuate and the impact has been rather small.”

“The skin cancer rates we have in New Zealand have nothing to do with the ozone hole,” he adds. “They’re primarily to do with a displaced population with the wrong skin type spending too much time in the sun in the summer.”

That’s right: the most significant reason New Zealand and Australia have the world’s highest skin cancer rates is due to colonialism and immigration. The overwhelming majority of skin cancers in New Zealand are found in Pākehā with skin types evolved to suit lower UV levels. As well as having naturally lower UV levels, the UK is also at a far higher latitude than many people realise, and consequently the peak UV levels are about half that found in New Zealand. British and northern European skin types just aren’t evolved to cope with the UV levels here. 

Consequently, skin cancer rates among Māori – who have evolved skin types suited to the UV levels here – are generally five times lower than for Pākehā. The latest figures show that in 2022, an incredible 96% of the 3,116 melanoma registrations were for European/other ethnicity, and only 2.6% (81) for Māori, 0.5% (16) for Pasifika and 0.25% (8!) among Asian ethnicities.

“If there were no ozone hole, we’d still have high skin cancer rates in New Zealand,” McKenzie says. “But the rates will go down in future as a lot of the immigrants to New Zealand have darker skin types that are more suitably adapted to the UV levels we get here.”

Another important factor behind our high skin cancer rates is that, despite being closer to the equator and having higher UV levels than Europe, New Zealand tends to be cooler because we’re surrounded by cold ocean. It’s a lot easier to spend all day in the sunshine when it’s 18 degrees in Invercargill than 35 degrees in Tangier, even though the burn-factor may be the same.

Mean measured UVI at noon for summer and winter for sites in NZ, compared with Australia and the UK, courtesy of NIWA.

But there’s more. The ozone hole forms over Antarctica every year between August and October, and then breaks up and ozone levels return to normal for the rest of the year. However, at its largest extent, it is nowhere near New Zealand, lying more than 1000km to the south. And when the ozone hole forms each year, New Zealand actually has the highest concentrations of ozone on earth, due to variations that lead to more ozone passing overhead here in spring.

Even in Antarctica, you’ll struggle to get a tan when the ozone hole is in effect due to the low angle of the sun at that time of year. UV levels at Scott Base in spring are about the same as in Auckland in winter, and peak UV levels on the continent are still during summer, when the sun’s rays are more direct.

Beyond the ozone hole, the whole world has experienced a general depletion in ozone levels due to historical CFCs and this has increased UV levels by less than 5% – but New Zealand isn’t any more affected by this than anywhere else, McKenzie says.

Another misconception is that UV levels in New Zealand are extremely high. UV levels are much higher at lower latitudes, closer to the equator, where the sun’s rays are more direct, and high-altitude places like the Andes and Tibetan Plateau.

In Invercargill, the UV Index typically peaks at seven at midday in January, while UV levels in Auckland typically peak at 10 (despite the former being closer to the ozone hole). But further north, in Darwin, levels average 13 at midday in summer, and they regularly peak in the mid-to-high teens closer to the equator. The highest UV levels in the world occur in the high altitude Altiplano plateau in Peru, where UV levels peak at 25.

However, peak UV levels here are naturally about 40% higher than similar latitudes in the northern hemisphere. Lower levels of pollution and dust in the southern hemisphere accounts for about half of this difference; the clearer air lets more UV through. 

The southern hemisphere also has naturally lower levels of ozone due to the way the gas is transported around the globe, which blocks less UV here. And by chance the southern hemisphere is about 3% closer to the sun in summer due to a quirk in the earth’s elliptical orbit. This makes UV levels here about 7% higher than in the north.

To help people understand how UV levels change through the day, and throughout the year, McKenzie has helped to develop an app, UVNZ, which shows the current and peak UV levels for your location. 

This isn’t to say that ozone depletion wasn’t a serious issue or that fears about the ozone hole were overblown. It has been estimated that if CFCs continued to be produced, there would have been an additional two million skin cancer cases each year by 2030. Fortunately, despite a particularly large ozone hole forming over Antarctica last spring, it has been gradually decreasing and the ozone is expected to return to normal by mid-century. 

“Ozone depletion would have had a major effect but because of the huge success of the measures used to control the problem it never became a major issue,” McKenzie says.

Keep going!