GENEVA: The Antarctic ozone hole has swelled this month to one of its biggest sizes on record, UN and US scientists say, insisting that the Earth-shielding ozone layer remains on track to long-term recovery but residents of the southern hemisphere should be on watch for high UV levels in the weeks ahead.
The World Meteorological Organisation, in a regular bulletin released on Thursday, said the Antarctic ozone hole often faces seasonal and year-to-year variations, but says the expansion this year shows "we need to remain vigilant".
The Geneva-based UN agency pointed to Nasa data on October 2 showing the hole had reached 28.2 million square kilometres - larger than the size of Russia and Canada put together.
It was the largest recorded on that date, and the hole has remained at a record size on the dates since, WMO said.
According to Nasa, the record largest ozone hole dates to September 9, 2000, when it was 29.9 million square kilometres.
Paul Newman, chief scientist for earth sciences at Nasa's Goddard Space Flight Centre in Greenbelt, Maryland, said prolonged wintertime conditions in the Antarctic region were persisting longer than usual, and that unusually weak vertical energy flows were among major contributors to the exceptionally large hole.
The stratospheric ozone layer, which sits some 25 kilometres high and protects against harmful UV rays, is different from the ground level ozone that is a harmful pollutant.
The ozone layer had been thinning since the late 1970s because man-made chlorofluorocarbons often used as refrigerants and aerosol cans released chlorine and bromine that destroyed ozone molecules high in the air.
A widely respected international accord in 1987 to phase out use of ozone-depleting chemicals has underpinned hopes for recovery of stratospheric ozone worldwide by 2070.
WMO and Nasa say the one-off expansion of the ozone hole this year will have little to no impact on the overall trend toward that goal.
Newman said the particularly strong El Nino this year was "the first thing that comes to your mind" but added there was no evidence yet of any connection between that and the larger ozone hole, and scientists will need time to explore the possible causes.
He also said Nasa model simulations have generally turned up very little effect on the Antarctic ozone hole from climate change and an increase in heat-trapping greenhouse gases in the atmosphere.
