August 23, 2005

Antarctic ozone hole grows from last year-WMO

GENEVA (Reuters) - 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 Organization (WMO) said on Tuesday.

The UN 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 15-30
km (9-19 miles) 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 sq km
(11 million sq miles) in September 2003, exposing the southern
tip of South America.

The WMO said on Tuesday 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 km.

"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
"leveled 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.