U.N. sees Antarctic ozone depletion at 'unprecedented' rate

GENEVA - The hole in the ozone layer is now three times larger than the United States - its biggest size ever, scientists at NASA said Friday. U.N. weather experts said the hole over the Antarctic is growing earlier in the year than usual.

Measurements of ozone depletion vary from year-to-year, making it difficult for scientists to determine the long-term environmental impact of changes in the ozone layer. Still, this year's hole - large and early - caught atmospheric experts off-guard.

''The fact that it's real big right now is kind of a surprise,'' said Dr. Paul A. Newman of NASA's Goddard Space Flight Center in Greenbelt, Md.

The center detected an ozone hole of about 11 million square miles on Sept. 3. That was the biggest ever, beating the previous record of 10.5 million square miles on Sept. 19, 1998, it said.

In Geneva, the U.N. World Meteorological Observation said stations in the Antarctic reported decreases in ozone of between 10 percent and 50 percent compared with the period between 1964 and 1976, before the ozone hole was observed. Though ozone levels decrease each year starting in July, such a large drop was ''unprecedented'' this early in the season, the WMO said Friday.

''It is remarkable to find these low values so early in September, perhaps one or two weeks earlier than in any previous year,'' the agency said.

Experts stressed that atmospheric variations from year to year combine with man-made gases to determine the hole's size. They said they can't be certain what the measurements mean for the rest of this year and beyond.

Depletion of the ozone layer over Antarctica and the Arctic is being monitored because ozone protects Earth from harmful ultraviolet radiation. Too much UV radiation can cause skin cancer and destroy tiny plants at the beginning of the food chain.

Antarctic ozone depletion starts in July, when sunlight triggers chemical reactions in cold air trapped over the South Pole during the Antarctic winter. It intensifies during August and September before tailing off in October as temperatures rise.

Circular winds, known as a vortex, trap air, giving chemicals the chance to react with the ozone.

''The polar vortex is bigger this year - bigger than 1998,'' Newman said. ''The containment vessel is larger and so the size is larger.''

Its size raises concerns that ''we're perhaps beginning to see some evidence of climate change in the stratosphere,'' although no firm evidence is available, he said.

''Maybe we have to be a little more serious about looking at this problem of the interaction of global warming and stratosphere cooling and ozone loss,'' he added.

The strength of the vortex means the ozone hole may persist a few days longer than usual, breaking up in December, Newman said.

Human-made chlorine compounds used in refrigerants, aerosol sprays, solvents, foam-blowing agents and bromine compounds used in firefighting halogens cause most ozone depletion.

The temperature over Antarctica also contributes significantly to the size of each year's hole. Starting in October, warmer temperatures reduce the ability of chlorine and other gases to destroy ozone.

''It's driven just about as much now by the temperature of the air as by the amount of fluorocarbons in there,'' said Russ Schnell, deputy director of the National Oceanic and Atmospheric Administration's climate change laboratory in Boulder, Colo.

Newman said he expects that ozone levels inside the Antarctic area covered by the hole will continue to drop over the coming week, but he said the area of the hole has stabilized over the past week and is unlikely to grow significantly.

''The true story won't come out for another three or four weeks,'' Schnell said.

Experts agree that the man-made chemicals are leveling off thanks to the Montreal Protocol, which commits countries to eliminating production and use of ozone-depleting substances. But it could be 20 years before ozone levels recover noticeably.

''There's going to be ups and downs on the long-term trend but the feeling is that we've probably bottomed out,'' Schnell said.

Joe Farman, a consultant at the European Ozone Research Coordination Unit in Cambridge, England, said this year's hole is the biggest for this time of year, though it is not that much larger than 1996 or 1998.

But ''one thing's quite clear - there's no sign of recovery yet,'' he said.