Ocean currents play a key role in connection with regional climate. Water masses from warmer areas like the equatorial belt transport large quantities of energy in the form of heat into cooler areas like Western and Central Europe, thus contributing to a moderate climate.
The North Atlantic Deep Water circulation is driven by two "pumps" - one in the Greenland Sea and one in the Labrador Sea - where cold, salty water sinks to the bottom and flows south, causing warmer water at the ocean surface to flow north to make up the difference, and warming the coast of Europe along the way.

Changes in either salinity or temperature at the sites where the water sinks can affect how fast the pump operates, and scientists have postulated that climate warming will increase inputs of fresh water into this region - due to higher precipitation as well as melting ice - reducing salinity and thereby slowing the rate at which the water sinks in the northern seas.

Scientists have long discussed the possibility of a slowdown or even cessation of the North Atlantic ocean circulation system as a result of global warming, but until now the discussions have been mostly theoretical. However, several teams of researchers are now uncovering signs that their concerns may be justified.

A team of researchers at the Scottish Executive's Marine Laboratory (Aberdeen) has found that the salinity of deep waters flowing south past Scotland has dropped about 0,01 grams of salt per kilogram of seawater per decade over the past two decades, decreasing its density as well.

Meanwhile, researchers at the Fisheries Laboratory of the Faroe Islands have found that deep water outflow in that region appears to be getting warmer, another sign that circulation patterns may be changing.

And a researcher team of Norway has discovered that one circulation pattern has already changed direction. Deep water from the Greenland Sea used to flow south into the Norwegian Sea at the rate of some 10 centimeters per second, but the researcher's measurements showed that in 1992 and 1993, the flow was in the opposite direction, a sign that the Greenland Sea pump has been dramatically reduced in power.

• There would be pronounced cooling in Western and Central Europe, as warm ocean currents (Gulf Stream) would no longer be present.
• The number of severe weather phenomena and climate fluctuations over decades would probably increase dramatically during the transition period (ca. 100 years).
• The global effects would be highly uncertain.
• A new climate state might last for centuries or millennia.

Further informations:

• Ocean Circulation Model
• Climate Change Impacts - an interactive informationsystem on the regional impacts of climate change