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Most scientists blame people, at least in part, for global warming.
Now, some researchers say people may be partly to blame for the
cooling of Antarctica as well.
While average global temperatures have risen about one degree Fahrenheit
over the past century, Antarctica over all appears to have cooled
slightly in the past few decades.
That has been puzzling, because the polar regions are thought to
be more sensitive to warming trends than the rest of the globe.
Even more puzzling, a small portion of Antarctica — the peninsula
that stretches north toward South America — defies the cooling trend.
It has been warming very rapidly, about five degrees over the past
50 years, 10 times the global average.
Writing in today's issue of the journal Science, Dr. David W. J.
Thompson, a professor of atmospheric science at Colorado State University,
and Dr. Susan Solomon, a senior scientist at the National Oceanic
and Atmospheric Administration in Boulder, Colo., argue that the
ozone hole, which has opened up each spring over Antarctica in recent
years, may help explain both contradictory trends.
"Ozone seems to be capable of tickling the Southern Hemisphere
patterns," Dr. Thompson said in an interview.
A vortex of winds continually blows around Antarctica, tending
to trap cold air at the South Pole. In the newspaper, Dr. Thompson
and Dr. Solomon show that the winds have strengthened in the past
few decades, keeping the cold air even more confined.
The peninsula, which lies outside the wind vortex, escapes the
cooling effect, the scientists said.
They say the ozone hole may be the cause of the stronger winds.
"That's where we speculate," Dr. Thompson said, "and the emphasis
is on the word `may.' "
Close to the ground, ozone, a molecule consisting of three oxygen
atoms, forms a large and unhealthy component of smog. High in the
atmosphere, however, naturally occurring ozone is essential for
life, blocking ultraviolet rays that would fatally mangle DNA.
Artificial chemicals known as chlorofluorocarbons, or CFC's, once
ubiquitous in aerosol spray cans and air-conditioner coolant, cause
a chain of reactions that destroy ozone. In September 2000, the
ozone hole opened up to a record 17.1 million square miles. With
the most damaging CFC's now phased out, the ozone hole is expected
to heal over the coming decades.
Until it does, however, fewer ozone molecules mean the atmosphere
absorbs less ultraviolet radiation. Instead of warming the air,
the rays bounce off the snow and ice of Antarctica and reflect back
into space.
Scientists already knew that the ozone hole had cooled the upper
atmosphere. Dr. Thompson and Dr. Solomon show that the troposphere,
the lowest six miles of the atmosphere, has also cooled.
"It's a lot of food for thought in there," said Dr. John E. Walsh,
a professor of atmospheric science at the University of Illinois
and an author of a paper in Science in January that indicated Antarctica
was cooling.
Dr. Walsh said the data tying the cooling to stronger winds was
convincing. "My one reservation," he said, "is the link to the ozone."
He noted that the ozone hole was usually largest in November or
December, but that the greatest cooling had been about six months
later.
Dr. Thompson agreed that the ozone hole could not explain the whole
climactic picture, and said other influences like ocean currents
probably played important roles, too.
"I seriously doubt it's the only player," he said. "I think it's
one of many."
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