Changing ocean currents

The ocean currents that circle the North Atlantic ocean could be affected by melting ice in the Arctic. If this happens, air temperatures in Britain, northwest Europe, and the east coast of North America could drop by up to 5 degrees in as little as a decade.

Ocean currents today

Ocean currents have a major effect on climate.

In Britain, winters are very mild. Parts of Siberia are on the same latitude (distance north) as Britain, but winter temperatures there are regularly well below zero. Britain’s milder winters are caused by an ocean current called the Gulf Stream.

There are ocean currents all over the world. These include circular currents in the north and south of the Pacific and Atlantic Oceans, and one that travels around Antarctica.

All of the ocean currents together are sometimes called the Ocean Conveyor, because they act like a giant conveyor belt that carries water around the world's oceans.

How the Gulf Stream works

The Gulf Stream, in the North Atlantic Ocean, carries warm salty water from the equator up to the coast of Greenland in the Arctic. This water travels near the surface of the ocean, because warm water isn’t very dense.

As it travels to the Arctic, the warm water heats the countries of the North Atlantic, like Britain. It then cools, which increases its density. The dense water sinks to the bottom of the ocean where it is carried back to the equator.

Effects of melting ice

Global warming is making the Greenland ice cap begin to melt.  If this happens rapidly, the meltwater, which is fresh, will flow into the North Atlantic and dilute the salty equatorial water.  This will make it less dense and stop it from sinking. It could stop the Gulf Stream completely.

If this happened, winters in Britain could be up to 5 degrees colder. It would have a severe effect on agriculture, the economy, and the wildlife that lives in the UK.

At the same time, the Earth as a whole would continue to suffer from global warming, which could reduce the effects of localised cooling in the North Atlantic, but may not stop them completely.

Past changes in ocean currents

The study of past climate shows that the Gulf Stream has stopped several times in the past, causing rapid climate change.

At the end of the last ice age, the melting ice disrupted the ocean currents in the North Atlantic and caused a drop in temperature of almost 5 degrees. Even though the rest of the planet was warming up, the North Atlantic region remained in a cold period for 1300 years.

The same thing happened around 8000 years ago, when the cooling lasted about a hundred years, and it could happen again today.

Even a short period of cooling in the North Atlantic could have a dramatic effect on the wildlife, and the human populations, living there.

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