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The Antarctic and Greenlandic icecap play an important role in the climatic system. They are an archive for the climate and a decisive climatic factor. Data from this archive can help us to study long-term climatic developments.
How is this possible? Snow that fell over several hundreds of
thousands of years under continuous low temperatures became ice
by metamorphosis. The snow that falls on a certain point on the
Greenland inland ice, is covered by the next falling snow and
pressed together, until after some time ice is created by
continuous compacting changing crystallization. During this
process the air that filled originally the space between the snow
crystals, is locked up. So the air bubbles contain the atmosphere
of past times. Analysis of this air gives propellant
concentrations. The corresponding temperature is determined by
measuring the ratio of the heavy oxygen and nitrogen isotopes, of
which the ice consists. Of course only in the centre you can find
the oldest ice because only there the ice is not transported to
the borders of the inland ice. 
At 3200 metres altitude, the highest point and probably the
centre of the Greenland inland ice, the Greenland Icecore
Project (GRIP), an international scientific cooperation,
worked there from 1989 to 1992 to unlock the archive. In four
summer campaigns they succeeded to make a 3029 metres deep drill
in the icecore down to the bedrock.
On the image you can see what data the icecore research gives us.
The lower part shows the temperature changes of the last 50,000
years. 10,000 years ago the "warm"-age started (the
intermediate ice age), in which the temperature are relatively
stable, i.e. we have a relatively stable climate at present.
But look at the preceding "cold"-age, the ice age, when the temperature was 10C lower on the average and submitted to rapid changes, characteristic for an unstable climate.
In the upper part of the graph you see the changes in the
methane, a propellant, concentration. In cold times there was
less methane in the air than in warmer times. You see clearly
that methane concentration and temperature change simultaneously.
So increase of the propellant concentrations does not necessarily
mean a temperature increase. Strange is that the temperature
increase some 5000 years ago, does not have an increase of the
methane concentration. The cause is maybe a lower natural methane
production.
The Intergovernmental Panel on Climate Change (IPCC)
is working on a climate report, which will be issued in 2001. In
this report attention will be paid to rapid climate changes,
discovered in the Greenland icecap. The last 10,000 years the
climate is stable, not to say boring compared to 11,000 to 12,000
years ago, a period called Young Dryas when the temperature
varied 7 degrees every ten years or so. An important question is
if it is possible that we will be confronted with rapid climate
changes in the near future. Is man responsible for those changes
by emitting propellants?
An hypothesis is that these rapid climate changes are caused by stopping the global water circulation in the oceans. Warm and salt water is transported from the tropics along the North American coast to the north. Surface water cools down when it streams more and more to the north. Colder water is heavier than warm water. At the Greenland coast this cold and very salty water has become so heavy it "sinks" to very low depths and flows back to the tropics.
This circulation determines the climate. The Warm Current e.g. is part of this global circulation. When this circulation stops the climate will change dramatically. When will this happen? When a big amount of sweet water flows from the north into the North-Atlantic Ocean. This sweet water can come from the Greenland icecap and can spread over a broad surface. This will make the surface water lighter. The salt water will not sink to the lower depths. The global water circulation will stop gradually. After some 1000 years the circulation will restart little by little. Much sweet greenlandic icecap water can flow into the oceans when there falls more precipitation, in other words when the gaining and losing of the icecap is out-balanced (see above). More precipitation is probably caused by an increase of propellant concentrations. But the concentration of propellants has to be four times higher than at the moment to give enough precipitation. Fortunately one expects that the propellant concentration will only double the next 100 to 200 years, which will rise temperature with 2 degrees C and give a changed precipitation pattern. An important issue is if that will slow down and eventually stop the global water circulation.
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