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Swollen
Ozone Hole Over The South Pole
High above
the icy continent of Antarctica, ESA’s Envisat spacecraft is
keeping watch - and what its instruments see is rather disturbing.
Freezing temperatures and man-made chemicals are combining to cause
a ‘hole’ in the layer of ozone gas. And this year’s
ozone hole looks like being one of the biggest on record. By mid-August
2005 it had already swollen to an area of 10 million square kilometres
– about the same size as Europe. And it was expected to expand
even more during September.
The ozone
hole was first discovered in the mid-1980s, and ESA satellites have
been studying the ozone hole continuously since 1995. Their records
show that only the ozone holes of 1996 and 2000 were larger at this
time of year. Ozone is a form of oxygen. Small amounts of ozone are
found in the stratosphere, between 20 and 50 km above the Earth. Fortunately
for us, the ozone layer gives us protection from solar ultraviolet
radiation that can cause skin cancer. However, chemical reactions
involving human-produced chlorine in high level clouds are destroying
the ozone. As the polar spring arrives, the combination of returning
sunlight and chlorine chemistry causes ozone molecules to split into
oxygen. A single molecule of chlorine can break down thousands of
molecules of ozone.
Information
from Envisat is vital for monitoring the seasonal changes in this
protective layer. The satellite data are fed to a near-real time ozone
monitoring and forecasting service made up of more than 30 partners
from 11 countries. Have you ever suffered from sunburn? This burning
of the skin is caused by ultraviolet (UV) light from the Sun. Serious
burning is not only painful, but it may cause skin cancer. Fortunately,
almost all of the harmful UV radiation is absorbed by a layer of ozone
gas 20 – 50 km above the Earth. However, ozone is a form of
oxygen that can be destroyed easily by certain man-made chemicals.
In 1987, the leading industrial countries agreed to phase out these
chemicals. Even so, satellites have shown that thinning of the ozone
layer has continued over Antarctica. The ozone hole reached a record
size – nearly 30 million sq. km - in 2000. Smaller ozone holes
have also appeared over the Arctic. These holes allow more UV light
to reach densely populated areas of Europe.
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