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Large ozone losses over the Arctic

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  • Mike Neuman
    Large ozone losses over the Arctic Cambridge Network Release date: 29 Apr 2005 Large scale ozone losses have occurred above the Arctic this past winter with
    Message 1 of 1 , May 5, 2005
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      Large ozone losses over the Arctic
      Cambridge Network
      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
      half century.

      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;
      email: John.Pyle@...

      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:

      reference: http://www.ozone-sec.ch.cam.ac.uk
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