Worldwide, seawater moves in a pattern of currents known as thermohaline circulation, or the global ocean conveyor. The currents flow because of differences in water density and move between the deep and surface ocean. 

Credit: Argonne National Laboratory

In the North Atlantic, water heated near the equator travels north at the surface of the ocean into cold, high latitudes where it becomes cooler. As it cools, it becomes more dense and, because cold water is more dense than warm water, it sinks to the deep ocean where it travels south again. More warm surface water flows in to take its place, cools, sinks, and the pattern continues. 

However, melting Arctic sea ice and melting Greenland glaciers could change this pattern of ocean currents, or stop it altogether.

Recent research shows that Arctic sea ice is melting due to climate warming. The melting ice causes freshwater to be added to the seawater in the Arctic Ocean which flows into the North Atlantic. The added freshwater makes the seawater less dense. This has caused the North Atlantic to become fresher over the past several decades and has caused the currents to slow. 

Water that is less dense will not be able to sink and flow through the deep ocean, which may disrupt or stop the pattern of ocean currents in the region. Scientists estimate that, given the current rate of change, these currents could stop within the next few decades.

What would happen if Atlantic ocean currents stopped?

Even though warming is causing the disruption to ocean currents, stopped or slowed currents in the North Atlantic would cause regional cooling in Western Europe and North America. The ocean currents carry warmth from the tropics up to these places, which would no longer happen. If the currents were to stop completely, the average temperature of Europe would cool 5 to 10 degrees Celsius. There would also be impacts on fisheries and hurricanes in the region.

The currents in the North Atlantic are part of a global pattern called thermohaline circulation, or the global ocean conveyor. If they were to stop, this would not be the first time that the global ocean conveyor was halted. There is evidence from sedimentary rocks and ice cores that it has shut down several times in the past which caused changes in climate. One of the most well-known, called the Younger Dryas Event, happened about 12,700 years ago and caused temperatures to cool about 5 degrees Celsius in the region.