What’s the Global Conveyor Belt?

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The global conveyor belt is the name given to the major circulation system in the world’s oceans. Ocean water circulates on a global scale, forming flows known as thermohaline currents, as they are driven by temperature and salinity. The flows form large-scale rings consisting of warm surface currents and cold, deep currents. These connect where warm water cools and sinks and where cold, deep water warms and rises. It has been estimated that the global conveyor belt takes about 1,000 years to complete a single cycle.

When seawater freezes in the Arctic region of the North Atlantic, salt is left in the remaining water, increasing its salinity and density and causing it to sink. Warmer water from further south flows to take its place, while cold, salty water flows south at a deeper level, eventually approaching the Antarctic coast. Here the flow splits into two veins, one enveloping the Indian Ocean and the other forming a larger loop around the Pacific Ocean. As water flows north into these oceans and toward the equator, it begins to warm up, becoming less dense and rising to the surface north of the equator. When it meets landmasses in the northern parts of these oceans, the water turns south again, then returns west into the Atlantic, turning north to complete the cycle.

The global conveyor belt has a major impact on climate. For example, warm water flowing across the North Atlantic towards the Arctic has a moderating effect on winter temperatures in NW Europe, resulting in a much milder climate than other areas at similar latitudes. Without the global conveyor belt, the UK’s climate would resemble that of Alaska.

It has been suggested that the global conveyor belt has slowed down, been reduced or stopped altogether at times in the past. This could be due to the melting of ice sheets and glaciers in the Arctic region, for example the Greenland ice sheet. The influx of fresh water would have reduced the salinity of ocean water, preventing it from sinking and causing it to freeze at a higher temperature. Without sinking water in the Arctic, the flow of warm water northward would cease; this would result in an abrupt change to a much colder climate in northern Europe. Some evidence suggests that cold snaps in northern Europe over the past tens of thousands of years have coincided with large-scale melting of Arctic ice sheets and glaciers.

There are fears that climate change could bring the global conveyor belt to a halt again, drastically cooling the climate of northern Europe. Evidence suggests that temperatures are rising over the Arctic, resulting in the melting of parts of the Greenland ice sheet. Some scientists fear that large amounts of fresh water from melting ice could reduce the salinity of seawater enough to keep it from sinking, effectively shutting down the conveyor belt.

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