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Geneva - The winter hole in the ozone layer above Antarctica appears to have grown from last year but is still smaller than in 2003, when it was at its largest, the World Meteorological Organisation (WMO) said on Tuesday.
The United Nations agency's top ozone expert added that seasonal depletion of the protective gas layer, which filters harmful ultraviolet rays that can cause skin cancer, may become more pronounced in the near future before the problem diminishes.
Large reductions in the ozone layer, which sits about 15km to 30km above the Earth, take place each winter over the polar regions, especially the Antarctic, as low temperatures allow the formation of stratospheric clouds that assist chemical reactions breaking down ozone.
The WMO said meteorological data showed last winter was warmer than in 2003 but colder than in 2004.
"At this stage it looks like this year's ozone hole will be quite average or maybe a little above average," Geir Braathen, WMO's ozone expert, told a news briefing.
Scientists say the hole spanned a record 29 million square kilometres in September 2003, exposing the southern tip of South America.
The WMO said on Tuesday that the area where temperatures are low enough for clouds to have formed - an indication of the potential hole size - now covered about 25 million square kilometres.
"This area is near the 1995-2004 mean and higher than observed in 2004 but somewhat lower than in 2003," it said.
Industrial chemicals containing chlorine and bromine have been blamed for thinning the layer because they attack the ozone molecules, causing them to break apart. Many of the offending chemicals have now been banned.
Concentrations of such ozone-depleting substances have "levelled off" and are set to decline, Braathen said.
"We still expect the ozone hole to appear annually and it actually might be a little bit worse in the next five to 10 years, then the situation will start to improve," he said.
"It will still take several decades before these substances have disappeared from the atmosphere. We expect the annual recurring ozone hole to take place until maybe mid-century."
The Geneva-based WMO, which has 181 member states, bases its analysis on data collected from satellites, ground-based observations and balloons launched into the atmosphere.
izvor
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