This year's ozone hole over the South Pole is one of the worst, despite scientists only a year ago saying it had shrunk to its smallest size.
By September 12 the hole above Antarctica was 26 million square kilometres, Nasa and the National Oceanic and Atmospheric Administration said.
The hole – which grows each spring and then shrinks again each year – was among the 10 worst since records began 26 years ago. Colder-than-average temperatures in the stratosphere had caused the larger-than-average ozone hole, said Paul Newman, chief scientist at Nasa's Goddard Space Flight Center.
The revelation comes only 10 months after data from the National Institute of Water and Atmospheric Research showed the hole to be the smallest in five years. The hole, which formed in the 1970s, shrunk last December to 22 million sq km. Those measurements had been in decline for five years and lagged far behind the record set in 2000, at 29 million sq km.
Yesterday, University of London Emeritus Professor of Photodermatology John Hawk – also a Cancer Society spokesman – said there was a common misconception that ozone holes significantly increased cancer-causing ultra-violet radiation getting through to Earth.
"Essentially, it's not very much extra light compared with the amount of ultra-violet that comes through anyway."
However, the amount of ultra-violet light in New Zealand was two to three times stronger than fair-skinned, originally European people were meant to be exposed to.
The ultra-violet levels in New Zealand meant our skin cancer rates were much greater than in Europe.
If the ozone layer was to deplete significantly further, the amount of ultra-violet light reaching Earth would increase drastically and skin cancer rates would then soar.
An effective worldwide ban on CFCs in 1987 meant the ozone hole was decreasing in size over decades.
Niwa chemistry-climate modeller Olaf Morgenstern said the ozone hole over Antarctica would break up during November or December.
But some of the ozone layer would become thinner over New Zealand.
"This will reduce the ozone layer somewhat during summer ... contributing to the high prevalence of skin cancer here."
- The Dominion Post
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