GENEVA, Oct 16 (Reuters) The hole in the ozone layer over Antarctica is ''relatively small'' at about 25 million sq km this year, but it will still take decades for it to heal over, the World Meteorological Organisation (WMO) said today.
The ozone hole, about the size of North America, appeared earlier than usual in 2007 developing in August and is the third smallest in the past decade.
''The Antarctic ozone hole of 2007 is relatively small. This should not be taken as a sign of ozone recovery,'' Geir Braathen, a WMO senior scientific officer, told a news briefing.
The ozone layer shields the Earth from damaging ultra-violent rays that can cause skin cancer.
The small ozone hole is due to relatively mild temperatures in the Antarctic stratosphere during the 2007 winter, as low temperatures increase ozone loss, he explained.
The WMO and the UN Environment Programme (UNEP) have said the ozone layer would likely return to pre-1980 levels by 2049 over much of Europe, North America, Asia, Australasia, Latin America and Africa. But in Antarctica, recovery would likely be delayed until 2065.
However, increasing amounts of greenhouse gases in the atmosphere mean more severe ozone holes could develop in coming decades.
In 1987, governments agreed the UN's Montreal Protocol to phase out chemicals, from refrigerants to hairsprays, that were found to be depleting the ozone layer.
Tightening the deal, 191 nations agreed in Montreal in late September to eliminate ozone-depleting substances 10 years ahead of schedule, which Canadian Environment Minister John Baird called a ''pivotal moment'' in the fight against global warming.
That UN-backed accord will phase out the production and use of hydrochlorofluorocarbons (HCFCs) for developed countries by 2020 instead of 2030, and by 2030 instead of 2040 for developing nations.
REUTERS GL HT1745