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The 'Ozone Hole' - a thinning of the stratospheric
layer of ozone which shields all living organisms from solar ultra-violet
(UV) radiation - may well be one of the first global environmental
problems to be widely understood by the general public. It has
led to the Montreal protocol, effectively banning significant
emissions of chlorofluorocarbons, historically widely used in
aerosol propellants, air conditioning systems and insulation foams.
The phenomenon itself, however, is only partly understood. The
European Commission has funded research in this field for many
years, from an array of small projects to major international
flagship campaigns like the Third European Stratospheric Experiment
on Ozone (Theseo) 1998-2000. Theseo is a truly international study,
involving over 500 participants from 20 different European countries,
as well as Canada, Japan, Russia and the United States. Using
high-altitude balloons and aircraft, ground stations and satellites,
Theseo shed light on the chemical processes in the stratosphere
that control the ozone layer. For example, it studied local polar
stratospheric clouds, which, when chlorine and bromine compounds
are present, are responsible for reducing the ozone layer's thickness
over the Arctic and Europe by up to 60%. Theseo reinforced concerns
that, due to global climate change, Arctic ozone levels may continue
to decline despite the reduction in stratospheric chlorine levels
resulting from the Montreal Protocol.
As the ozone layer is thinning, the levels of particularly harmful
UV-B radiation are increasing over populated regions of Europe.
Other projects have therefore investigated the climatology of
atmospheric UV radiation and its possible effects on agriculture,
the ecosystems and human health, particularly in relation to immune
system problems and cancer.
Although
our understanding of the critical atmospheric processes has increased
dramatically, we still do not know enough. New numerical models,
for example, have correctly calculated the relative variations
in ozone loss observed over the Arctic, but consistently underestimate
the actual amount of ozone lost. More research is therefore vital
in order to predict how ozone levels could recover in the future.
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