Large ozone losses over the Arctic
Release date: 29 Apr 2005
Large scale ozone losses have occurred above the Arctic this past
winter with over 50% of the ozone destroyed at altitudes around 18
Scientists from the EU SCOUT-O3 Integrated Project, which is co-
ordinated by the University of Cambridge's Chemistry Department, have
been studying the links between stratospheric ozone and climate
change in the Arctic since May 2004. This recent finding was
announced during a meeting of the European Geophysical Union in
Vienna earlier this week.
Overall temperatures in the ozone layer were the lowest for 50 years
and were consistently low for over three months. From late November
to late February, large areas of polar stratospheric clouds (PSCs) -
clouds in the ozone layer- were present over the Arctic region at
altitudes between 14 and 26 km. This is the largest in the 50 year
record, and especially in the last 20 years, the period when the
ozone-depleting compounds have been high.
The chemical balance in the stratosphere is changed significantly by
the presence of these clouds, altering the breakdown products from
manmade CFCs (chlorofluorocarbons) so that rapid chemical ozone
destruction can occur in the presence of sunlight. The cold
conditions affected the distribution of nitrogen oxides, allowing
ozone loss to continue longer than usual.
The European scientists reported the first signs of ozone loss in
January 2005. As sunlight returned to northern latitudes the rate of
ozone depletion increased and rapid destruction of ozone occurred
throughout February and March. In the altitude range where the ozone
layer usually reaches its maximum concentration, more than half of
the ozone was lost.
'Overall about 30% of the ozone layer was destroyed,' said Dr Markus
Rex from the Alfred Wegener Institute in Potsdam, Germany. 'This
largely prevented the normal seasonal increase of the thickness of
the ozone layer during winter and led to a thinner ozone layer in
Arctic spring compared to warmer years.'
The overall degree of ozone loss this year was of similar magnitude
to the record loss that was observed in the Arctic during winter
1999/2000. During late March the Arctic air masses drifted over
central Europe and contributed to individual days of significantly
increased UV-B radiation and sunburn risk in parts of Europe. The
affected region reached as far south as northern Italy.
Emissions of ozone depleting substances are now largely banned
worldwide by the Montreal protocol. As a first success of this
milestone of international cooperation in environmental policies the
atmospheric concentrations of CFCs started to decrease. But the
atmospheric lifetime of these compounds is extremely long and the
concentrations will remain at dangerously high levels for another
Over the next few decades the fate of the Arctic ozone layer will
mainly depend on the evolution of atmospheric temperatures at the
altitude of the ozone layer. Over the past forty years the conditions
there have become significantly colder.
'The cooling was particularly pronounced for the cold Arctic winters.
Unfortunately these are the winters that result in large ozone
losses. In 2005 the average extent of conditions cold enough for the
existence of polar stratospheric clouds was four times larger than it
has ever been in the sixties or early seventies of the past century,'
said Dr Rex.
This continuous cooling trend is qualitatively consistent with what
would be expected as a result of increasing concentrations of
greenhouse gases in the atmosphere. However the coupling processes
between climate change and temperatures in the polar ozone layer are
complicated by feedback process that are currently not sufficiently
understood to make reliable predictions for the future.
'Our aim is to improve the predictions of future ozone and other
stratospheric changes as well as the associated UV and climate
impact,' said Dr Neil Harris from the University of Cambridge, one of
the coordinators of the project.
'Within SCOUT-O3 we have followed the meteorological conditions in
the Arctic closely and a suite of atmospheric observations and model
calculations was triggered on a very short notice. The Arctic
ozonesonde station network started a campaign of coordinated
measurements to monitor the chemical ozone destruction.
'ESA carried out additional measurements of the chemical composition
of air in the Arctic ozone layer with the ENVISAT research satellite.
The high flying research aircraft Geophysica made a deployment deep
into Arctic air masses resulting in additional in-situ observations
of key species.'
Preliminary results from all these studies are being presented at the
European Geophysical Union meeting in Vienna this week.
SCOUT-O3 is a 5 year project receiving 15 million euros from the
European Commission Research DG's Global Change and Ecosystems
Programme and a similar amount of associated funding from national
The degree of Arctic ozone loss varies greatly from year to year. For
example, there were losses of <10% in 1998/99 and >65% in 1999/2000
at altitudes around 18 km, and losses of 50% or more have been seen
at around 18 km in several winters since the early 1990s. Chemical
losses in the total column of ozone over the Arctic have varied
between about 5 and 30% since the early 1990s. Overall a decrease in
total ozone in the Arctic region has been observed since 1980,
although there is considerable year-to-year variation in the observed
values. This variability in the ozone loss is to be contrasted with
the Antarctic where nearly complete ozone loss has taken place in all
except one winter since the late 1980s at altitudes between about 15
and 20 km.
The use of halogen-containing substances, such as chlorofluorocarbons
(CFC) and halons has led to an increase in the atmospheric
concentration of chlorine and bromine. The substances can cause ozone
depletion. The destruction of the ozone layer by man-made chlorine
and bromine is most effective under very cold conditions. Rapid ozone
loss can occur when temperatures drop below about -78°C, a value that
is sometimes reached in the Arctic ozone layer at about 20 km
altitude in winter. Since ozone destruction also requires sunlight,
the ozone loss process starts after a cold winter when the sun
returns to polar latitudes in spring.
More information on the ozone layer problem can be found at: Ozone
Hole Tour: http://www.atm.ch.cam.ac.uk/tour/index.html
UN Environment Programme: http://www.unep.org/ozone/index.asp
World Meteorological Organisation: http://www.wmo.ch/indexflash.html
For more information, contact:
1. Corina Hadjiodysseos, Press and Publications Office, University of
Cambridge, UK Tel: 01223 332300; email: ch250@...
2. Prof. John Pyle, University of Cambridge, Tel: 01223 336473;
3. Dr. Neil Harris, Department of Chemistry, University of Cambridge,
UK email: Neil.Harris@...
4. Dr. Markus Rex, Alfred Wegener Institute for Polar and Marine
Research in Potsdam, Germany Tel: + (49) 174 311 8070; email:
5. Dr Peter von der Gathen, Alfred Wegener Institute for Polar and
Marine Research in Potsdam, Germany Tel: + (49) 331 288 2128; email: