The New Zealand Herald of 5 September carried the headline “Ozone gap to lift skin cancer 7 per cent”.
Then followed a report from Dr Richard McKenzie of the National Institute of Water and Atmospheric Research at Lauder. He said that ozone loss in the past 15 years had caused an increase of 8-10% in the amount of harmful ultraviolet rays reaching Otago and Southland, and that UV levels were expected to rise another 2-3%, reaching a peak in about five years.
So far so good. We have no reason to question the quality of the research and his findings that ozone depletion over the southern region has increased UV penetration over the South Island plains. But Dr McKenzie is then reported as saying that:
Cancers caused by past depletion were only now beginning to appear as the disease often developed some years after exposure to the rays.
And that:
Small changes in UV can have large effects on life. There will be extra skin cancers and earlier deaths will result.
Surely Dr McKenzie has moved beyond his field of expertise. The recent increase in skin cancer is almost entirely attributable to the craze for sun-bathing and sun-tans which began in the 1920s and reached a peak during the early ’70s. Any impact of increased ultraviolet penetration is insignificant when compared to this “life-style” choice which encouraged young children to play at the beach all day, fully exposed to the sun, and teenagers to bask in full summer sun for hours on end in their quest for the perfect tan.
Furthermore, changes in the level of ultraviolet light reaching the ground are much more dependent on cloud cover, general atmospheric pollution, and geographic latitude than on any recorded or predicted variations within the ozone layer. A move from the Arctic to the equator increases annual exposure to UV by 4,000%. If Aucklanders are worried about a 10% increase in UV penetration they should move 200 km south to, say, Taupo.
I am prepared to bet $1,000 to $1 that there will be no increase in skin cancers attributable to increased UV over the next few years. The increases which occur will be attributable to the sun-burned baby-boomers growing up and contracting melanoma. This will peak and decline as a new generation of parents encourage their children to wear hats and use sun-blocks.
If Dr McKenzie can set up an experiment using a control population which stays where it is, in an atmosphere which remains as clear as it is today, and in which no-one reduces their exposure to intense sunlight or increases their use of sun protection, then that population might record the increase he forecasts. But such an experiment would be totally unethical, so the predicted outcome cannot happen. Hence my confidence in the bet.
In an interview Dr McKenzie conceded he was no expert in public health. Maybe he should have stuck to his field and let someone else draw the public-health conclusions. People have to deal with daily predictions of doom from all directions. There is no need to add a fear of UV-induced melanoma epidemics to the list. His forecast sounds unavoidable — and it’s not.
