By Olivia Colangelo

In simple terms, the Atlantic Meridional Overturning Circulation, or the AMOC, consists of ocean currents that carry warm water north and cold water south throughout the Atlantic Ocean. Marine scientists recently predicted a potential AMOC shutdown as soon as 2025.

The last AMOC shutdown occurred approximately 14,500 years ago when the current system experienced a significant slow down at the end of the Ice Age, propelling the Northern Hemisphere back into cold conditions.

Diagram of the AMOC current system. The system of currents which make up AMOC is comparable to a large conveyor belt which is controlled by the water’s density. (Photo courtesy of Woods Hole Oceanographic Institution).

The AMOC is a pivotal aspect of the global ocean circulation system. It includes a vast network of currents, such as the Gulf Stream, and is predominantly responsible for the movement of carbon, nutrients, and heat. As warm water from the tropics is transported to higher latitudes, it cools, becomes denser, and sinks to deeper parts of the ocean. This cold water then travels back towards the equator to finish its circulation. The AMOC helps transport warm water to Western Europe, moderating its climate and regulating global weather patterns. A potential slowdown could disrupt both temperature and precipitation in the region.

The AMOC has been steadily weakening over the past century, and officials predict that it will face erasure between 2025 and 2095. Since the 1950s, the AMOC’s primary current has slowed by about 15%. Climate studies and analyses attribute the shutdown to human-induced global warming. As glacial ice melts in the Arctic and Greenland (as a result of climate change), it causes an influx of freshwater into the North Atlantic. This added freshwater can decrease the density of the seawater, making it less likely to sink and disrupting the standard circulation pattern.

An AMOC shutdown would have dire impacts on climate throughout the Atlantic basin and beyond, but exactly how grave are the consequences? Repercussions include altered weather patterns, rising sea levels, and a loss of biodiversity within marine ecosystems. Modifications in ocean circulation may have an impact on atmospheric circulation, which may modify precipitation patterns and storm trajectories. The effects of the AMOC shutdown are comparable to that of La Niña, which causes temperatures to drop and rainfall to increase across regions.

A shutdown would further disrupt the rainwater that billions of people are dependent on for nutrients in India, South America and West Africa. Additionally, it would further endanger the Amazon rainforest and Antarctic ice sheets, while increasing storms and lowering temperatures throughout Europe.

It is important to note that predicting the exact timing of the AMOC shutdown is both challenging and uncertain. There is concern about the consequences of a shutdown, however it is difficult to precisely determine its exact timing and magnitude. Scientists continue to analyze this complex current system to acquaint themselves with its dynamics and long term impacts on the global climate. As we strive to limit our CO2 emissions, we keep the AMOC in check while limiting our carbon footprint.