Brussels, 05 Apr 2005
One of the most immediate consequences of a reduction in ocean circulation, such as the Atlantic overturning circulation, would be marked changes in local sea levels, according to scientists in Germany.
Deep-ocean circulation is driven by the density differences between water masses - the result of differences in their temperature and salinity. This constant circulation means that the ocean's surface is not flat, but rather has hills and valleys associated with the currents.
Anders Levermann and his colleagues from the Potsdam Institute for Climate Impact Research investigated the effects of a possible shutdown of the Atlantic overturning circulation. They found that this would cause a sea level rise of up to one metre in the northern Atlantic, and a corresponding drop in sea level in the southern Atlantic, as the ocean's hills and valleys level themselves out.
Furthermore, the team warns that unlike sea level changes due to global warming (which causes sea water to expand) or ice melt (which adds more water to the oceans), these changes would occur much more rapidly, following the circulation changes almost without delay.
To put that into perspective, while global warming and ice melt can lead to global sea level changes of tens of centimetres per century, a disruption in ocean circulation could result in changes of up to 2.5 centimetres per year in some regions. The regional effects on coastal areas of Europe and North America following such a sharp rise could be serious, the team adds.
The key question, therefore, is just how likely is it that the Atlantic overturning current will weaken or shutdown altogether? 'This is a question that is still being researched,' Dr Levermann told CORDIS News. 'Studies indicate that the circulation could be 'bi-state' with an off- and on-state, but this is not yet known for sure.'
'Many experts believe that there will be a future weakening in the overturning circulation, but estimate the probability of complete collapse at around only five per cent,' he added. Even if the chances of total collapse are slim, for Europe and many other regions of the world any prospect of weaker ocean circulation is a worrying one.
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