One of the most amazing systems our oceans boast is the “Great Conveyor Belt,” a mechanism which transfers heat from the tropics to higher latitudes. The system plays a critical role in supplying heat to the polar regions, which means it influences the rate of sea ice formation near the poles. But this conveyor belt is starting to lose steam: since the mid-1900s, the Atlantic Ocean’s circulation has slowed by approximately 15 percent. 

Wind is the force that powers this giant conveyor belt, bringing warm water from the tropics to the poles. As the wind carries warm water further north, the water cools down, making it denser. The water also begins to evaporate, which means the remaining water has a higher salt content, further increasing its density. This cold, salty water slowly flows back to the equator, where it warms up and starts to rise.  

This process, known as the thermohaline cycle, relies on two key factors: water temperature and salinity. This leaves the cycle vulnerable to drastic climate changes. Experts already expect increased amounts of rainfall and the melting of glaciers and sea ice in the coming decades as a result of global warming. 

These extreme changes will cause a large quantity of freshwater to mix with cold, salty water headed north. That means the salty water is less likely to sink, due to the lower salt content. Currently, as ice on Greenland melts, vast amounts of fresh water rush into the North Atlantic Ocean. This disruption threatens the operation of the entire conveyor belt.

As the conveyor belt slows down, carbon dioxide is less likely to reach deeper parts of the ocean. If the ocean is no longer storing this carbon, it only has one place to go: the atmosphere.

Global warming is accelerating the melting of Greenland’s ice, which is the main disruptor of the thermohaline cycle. Without aggressive actions to combat the emissions of greenhouse gases, we could see this historic Atlantic current be thrown into chaos, bringing the world deeper into the climate crisis.