Perilous
Times
Large depleted Ozone hole opens above the Arctic
by Staff Writers
Karlsruhe, Germany (SPX) Jan 20, 2012
Strongly reduced ozone values (left, dark blue) and significantly
increased concentration of chlorine monoxide (right, red) that is
directly involved in ozone degradation. (Figure: IMK-ASF, KIT).
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.