Ocean Circulation and Climate

If the ocean currents that transport warmth up from the Gulf Stream were ever to slow down or to shut down completely, the climate in Britain would be considerably colder - similar in fact to that of Moscow, which is on the same latitude. This event is known as Rapid Climate Change.

"The ocean plays a major role in transporting heat polewards, thus moderating the Earth's climate."
World Ocean Circulation Experiment

Scientists believe that Rapid Climate Change has happened before, about 13,000 years ago. A period of warming caused a massive ice sheet across the top of North America to melt which flushed huge quantities of fresh water into the North Atlantic Ocean. This flow of fresh water upset the process of thermohaline circulation and the Gulf Stream current shut down. Within 10 to 20 years of this happening, ocean temperatures around Britain had dropped by an average of 10°C. Sea ice reached as far south as 45°N - which is well beyond the UK's south coast. This mini-ice age lasted for 1200 years and is called the Younger Dryas Cooling.

It is impossible to say whether our present period of warming could cause the same thing to happen again. There isn't a North American ice sheet to melt any more, but climate change is causing ice caps to melt at both poles. The action of the fresh water from these ice caps entering the North Atlantic sea from Greenland and Russia could slow down the circulation of the ocean currents. This is something Britain and Norway are taking very seriously and carrying out a great deal of research into.

Surface and deep currents in the ocean combine to form what is known as the thermohaline circulation, more simply the 'great conveyor belt', which helps transport heat from the equator towards the poles.

The sea between Greenland, Iceland and Northern Norway is the main northern hemisphere region where surface water sinks into the deep, completing the three dimensional loop of ocean currents. The sinking is a result of relatively small changes in the density of seawater, its salinity and its temperature. Any changes to this delicate balance, for example an increase of warmer 'fresher' water provided by river and ice melt, could have the potential of changing the rate of flow and direction of the Great Conveyor Belt.

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