Ozone treaty reduced NZ cancer rates

In New Zealand 70,000 people are treated for skin cancer each year. Photo / Christine Cornege

Global chemical pact cut potential UV damage

New Zealand could today be facing even higher rates of skin cancer had the world not agreed to rein in ozone-depleting substances nearly 30 years ago.

In a study published in the journal Nature Communications today, scientists used a 3D atmospheric chemistry transport model to reveal what would have happened to the world's atmosphere without the restrictions introduced by the 1987 Montreal Protocol.

The global treaty restricted the use of substances such as chlorine and bromine, and since its signing, New Zealand has gradually phased out all controlled ozone-depleting substances.

Had the protocol not happened, the ozone hole over the Antarctic - on track to disappear by 2050 - would have been 40 per cent larger than it is today.

There would have also been further ozone declines over New Zealand and Australia, where people are more sensitive to UV damage.

While the two countries have the world's highest death rates from skin cancer, a model generated by the researchers predicted cancer risk would have increased when surface UV rates climbed by between 8 and 12 per cent.

Specifically, there could have been increases in incidence rates of the two most common forms of skin cancer - squamous and basal cell carcinoma - of 15 and 8 per cent respectively.

In New Zealand, about 70,000 people are treated for skin cancer each year, with around three-quarters basal cell carcinoma cases.

Potential impacts on rates of melanoma, which has a higher mortality rate and is diagnosed in 4000 new cases here each year, were less certain.

Niwa atmospheric scientist Dr Richard McKenzie, who co-authored the paper with British and Dutch scientists, said the potential health impacts would have been just the start of a far bleaker picture for the future. Along with other damaging, long-term consequences for the planet's atmosphere and climate, a "full blown" ozone hole would have appeared over the Arctic by 2011 for the first time, occurring regularly in subsequent springs.

Dr McKenzie said it was important to remember that UV risk remained over New Zealand, and there would probably always be higher UV levels here compared with corresponding latitudes in the Northern Hemisphere.