Geoscience Reference
In-Depth Information
This balance between the NADW and AABW is extremely important in maintaining our
present climate, as not only does it keep the Gulf Stream flowing past Europe, but it also
maintains the right amount of heat exchange between the Northern and Southern Hemi-
spheres. Scientists have shown that the circulation of deep water can be weakened or
'switched off' if there is sufficient input of fresh water to make the surface water too light
to sink. This evidence has come from both computer models and the study of past cli-
mates. Scientists have coined the phrase 'dedensification' to mean the removal of density
by adding fresh water and/or warming up the water, both of which prevent sea water from
being dense enough to sink. As we have seen, there is already concern that global warm-
ing will cause significant melting of the polar ice caps. This will lead to more fresh water
being added to the polar oceans. Climate change could, therefore, cause the collapse of
NADW, and a weakening of the warm Gulf Stream ( Figure 29b ). This would cause much
colder European winters and more severe weather. However, the influence of the warm
Gulf Stream is mainly seen in the winter and has only a small effect on summer temperat-
ures. So, if the Gulf Stream fails, global warming would still cause European summers to
heat up. Europe would end up with extreme seasonal weather very similar to that of
Alaska.
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