Long a consideration in the Antarctic, ozone levels in the Arctic
are now a cause for concern
The ozone layer has
seen unprecedented damage in the Arctic this winter due to cold
weather in the upper atmosphere.
By the end of March, 40% of the ozone in the stratosphere had
been destroyed, against a previous record of 30%.
The ozone layer protects against skin cancer, but the gas is
destroyed by reactions with industrial chemicals.
These chemicals are restricted by the UN's Montreal Protocol, but
they last so long in the atmosphere that damage is expected to
continue for decades.
"The Montreal Protocol actually works, and the amount of
ozone-depleting gases is on the way down, but quite slowly," said
Geir Braathen, a senior scientist with the World Meteorological
Organization (WMO), which co-ordinates ozone data globally.
"In the meantime, we have some winters that get much colder than
before and also the cold periods last longer, into the spring," he
told BBC News.
"So it's really a combination of the gases still there and low
temperatures and then sunshine, and then you get ozone loss."
Dr Braathen was one of a number of scientists presenting the
findings at the European Geosciences Union (EGU) annual meeting in
Vienna.
'Sun screen'
The destructive reactions are promoted by cold conditions (below
-78C) in the stratosphere.
While this is an annual occurrence in the Antarctic, where the
annual depletion has garnered the term "ozone hole", the Arctic
picture is less clear, as here the stratospheric weather is less
predictable.
“Start Quote
With no ozone layer, you would have
70 times more UV than we do now - so you can say the ozone
layer is a sunscreen of factor 70”
Geir Braathen
World Meteorological
Organization
This winter, while the Arctic was
unusually warm at ground level, temperatures 15-20km above the
Earth's surface plummeted and stayed low.
"The low temperatures were not that different from some other
years, but extended much further into March and April - in fact it's
still going on now," said Farahnaz Khosrawi, an ozone specialist at
the Meteorological Institute at Stockholm University, Sweden.
Another, Dr Florence Goutail from the French National Centre for
Scientific Research (CNRS), put the 2010/11 winter in context.
"Usually in cold winters we observe that about 25% of the ozone
disappears, but this winter was really a record - 40% of the column
has disappeared," she said.
The longer and colder Antarctic winters often see 55% of the
ozone depleted.
However, this has hardly any impact on human health, as the
region is largely uninhabited - only the southern tip of South
America sometimes comes under the ozone hole.
But in the Arctic, the situation is different.
Over the last month, severe ozone depletion has been seen over
Scandinavia, Greenland, and parts of Canada and Russia.
The WMO is advising people in Scandinavian countries and
Greenland to look out for information on daily conditions in order
to prevent any damage to their health.
Loss of ozone allows more of the Sun's harmful ultraviolet-B rays
to penetrate through the atmosphere. This has been linked to
increased rates of skin cancer, cataracts and immune system damage.
"With no ozone layer, you would have 70 times more UV than we do
now - so you can say the ozone layer is a sunscreen of factor 70,"
said Dr Braathen.
Snow fall
Ozone depletion is often viewed as an environmental problem that
has been solved.
The Montreal Protocol, established in 1987, and its successor
agreements have phased out many ozone-depleting chemicals such as
the chlorofluorocarbons (CFCs) that used to be in widespread use as
refrigerants.
Ozone data were captured using satellites and weather balloons
Use of some continues at a much lower level, with poorer
developing countries allowed more time in which to switch away from
substances essential to some of their industries.
But even though concentrations of these chemicals in the
atmosphere are falling, they can endure for decades.
In polar regions, the concentration of ozone-depleting substances
has only fallen by about 10% from the peak years before the Montreal
Protocol took effect.
In addition, research by Markus Rex from the Alfred Wegener
Institute in Germany suggests that winters that stand out as being
cold in the Arctic stratosphere are getting colder.
"For the next few decades, the [Arctic ozone] story is driven by
temperatures, and we don't understand what's driving this [downward]
trend," he said.
"It's a big challenge to understand it and how it will drive
ozone loss over coming decades."
Projections suggest that the Antarctic ozone hole will not fully
recover fully until 2045-60.
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