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by Staff Writers
Karlsruhe, Germany (SPX) Jan 20, 2012 Extraordinarily cold temperatures in the winter of 2010/2011 caused the
most massive destruction of the ozone layer above the Arctic so far: The
mechanisms leading to the first ozone hole above the North Pole were
studied by scientists of the KIT Institute of Meteorology and Climate
Research (IMK).
According to these studies, further cooling of the ozone layer may
enhance the influence of ozone-destroying substances, e.g.
chlorofluorocarbons (CFC), such that repeated occurrence of an ozone
hole above the Arctic has to be expected. About a year ago, IMK scientists, together with colleagues from Oxford,
detected that ozone degradation above the Arctic for the first time
reached an extent comparable to that of the ozone hole above the South
Pole. Then, the KIT researchers studied the mechanisms behind. Their
results have now been published in the journal "Geophysical Research
Letters". According to IMK studies, occurrence of the Arctic ozone hole was mainly
due to the extraordinarily cold temperatures in the ozone layer that is
located at about 18 km height in the stratosphere, i.e. the second layer
of the earth's atmosphere. There, chlorine compounds originating from chlorofluorocarbons (CFC,
e.g. greenhouse gases and refrigerants) and other pollutants are
converted chemically at temperatures below -78C. These chemical conversion products attack the ozone layer and destroy it
partly. One of the main statements in the study: If the trend to colder
temperatures in the stratosphere observed in the past decades will
continue, repeated occurrence of an Arctic ozone hole has to be expected. The team of IMK researchers analyzed measurements of the chemical
composition of the atmosphere by the MIPAS satellite instrument
developed by KIT. In addition, model calculations were made to determine
concrete effects of further cooling of the ozone layer. "We found that further decrease in temperature by just 1C would be
sufficient to cause a nearly complete destruction of the Arctic ozone
layer in certain areas," says Dr. Bjorn-Martin Sinnhuber, main author of
the study. Observations over the past thirty years indicate that the stratosphere
in cold Arctic winters cooled down by about 1C per decade on the
average. According to Sinnhuber, further development of the ozone layer
will consequently be influenced also by climate change. He points out that the increase in carbon dioxide and other greenhouse
gases will warm up the bottom air layers near the ground due to the
reflection of part of the thermal radiation by the bottom layer of the
atmosphere towards the earth's surface, but also result in a cooling of
the air layers of the stratosphere above, where the ozone layer is located. After the first discovery of the Antarctic ozone hole in the mid-1980s,
CFCs were rapidly identified to be the cause and their use was
prohibited by the Montreal Protocol of 1987. However, it will take
decades until these substances will have been removed completely from
the atmosphere. "Future cooling of the stratosphere would enhance and extend the impacts
of these substances on the ozone layer," says Dr. Bjorn-Martin
Sinnhuber. It is now necessary to study potential feedbacks on climate
change. The present study is embedded in long-term programs of IMK in this
field. In December, the researchers started a new measurement campaign
in the Arctic ozone layer in Northern Sweden using a high-altitude aircraft. Again, they encountered extraordinarily low temperatures. However, it is
not yet possible to predict whether temperatures will be low enough over
a longer term to cause a comparably large degradation of ozone in this
winter.
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