| By
Deborah Zabarenko
WASHINGTON
(Reuters) - Ozone-eating clouds that erode Earth's protection
against ultraviolet radiation are born in thin rings of
supercold air over the North and South Poles, scientists
reported on Thursday.
The
Sun's ultraviolet rays could cause skin cancer in humans
and biological damage to other living things if Earth were
not shielded by the ozone layer high in the atmosphere.
But polar stratospheric clouds made of nitric acid and water
deplete this protective layer.
Scientists
have known about the clouds for years, but U.S. researchers
have just discovered the bands of frigid air in the stratosphere
that help to create them, according to an article in the
current edition of the journal Science.
And
as the Earth's surface gets warmer, due to heat trapped
by so-called greenhouse gases, the stratosphere gets colder,
making it an even better place to create the ozone-depleting
clouds, NASA (news - web sites) researcher Azadeh Tabazadeh
said.
The
more these high polar clouds proliferate, the slower Earth's
recovery from ozone depletion, Tabazadeh said in a telephone
interview from the National Aeronautics and Space Administration's
Ames Research Center in California.
The
polar stratospheric clouds do their work by sucking nitrogen
out of the cold air. Because they are made up of large particles,
each the size of a bit of road dust, the clouds are heavy
and pull out the nitrogen as they fall toward Earth, Tabazadeh
said.
Nitrogen
is important because it reacts with the chlorine in human-made
chlorofluorocarbons (CFCs). Now banned under international
agreements, CFCs have long been identified as a prime cause
of ozone depletion.
The
polar stratospheric clouds pack a double punch, Tabazadeh
said: they take away nitrogen, which can mitigate the effects
of ozone depletion, and they also activate chlorine, which
spurs ozone depletion.
Still,
if Earth's climate stayed constant, the ozone layer should
start recovering because CFCs are being limited. But Earth's
surface climate is warming, which means the stratosphere
is cooling.
``The
surface warming causes a cooling in the stratosphere and
the cooling promotes more ozone depletion,'' Tabazadeh said.
''Global warming (news - web sites) is actually affecting
the ozone depletion.''
``I
think the best thing to do is try to control the global
warming issue,'' she said. ``And that could be controlled
by less emissions of greenhouse gases and also less emissions
of soot. It's very hard to regulate.''
|
