The hole in the ozone layer this year will probably be slightly smaller than the all-time largest of 2003, signaling that depletion is still occurring but possibly at a slower rate, a UN agency said.
"The size of this year's ozone hole is approaching an all-time high, but it will probably not break any records," said Geir Braathen, an ozone specialist at the World Meteorological Organization, told reporters on Friday.
"It's kind of leveling off, but it's still too early to say that the situation is improving," he said earlier at a news conference.
At present, the hole over Antarctica is about 27 million square kilometers and the WMO expects it to increase to about 28 million square kilometers -- a notch below its 2003 peak at about 29 million square kilometers.
Based on recent patterns, he expects the hole to hover around this year's size for a few more years before it could begin to shrink. Some scientists predict it will take about 50 years for the ozone hole to stop forming.
Braathen told the conference that a "so-called ozone recovery" has yet to be confirmed. "One could say that the depletion is maybe going at a slower rate than before."
Chlorofluorocarbons, or CFCs, once widely used in spray cans and refrigerators, deplete the Earth's protective layer. The hole has been forming in the extremely low temperatures that mark the end of Antarctic winter every year since the mid-1980s. The hole generally is biggest around late September, while the so-called ozone value does not bottom out until mid-October.
The ozone layer keeps out ultraviolet radiation, which is dangerous to humans and animals. Less protection could increase risks of skin cancer and cataracts and affect biodiversity, scientists say.
Nevertheless, Braathen warned it was too early to "sound the all-clear," and said global warming had started to reverse some of the positive developments.
"Global warming might actually delay the healing of the ozone layer or altogether worsen the issue," he said.
Braathen said agencies like his must continue to closely monitor the ozone layer via satellites and ground stations. Signatories to the anti-CFC treaty known as the Montreal Protocol, particularly developing countries that had less strict phase-out schedules, should respect the accord, he stressed.
More than 180 nations have signed the Montreal Protocol, which went into effect in 1997.