AMOC and Global Climate: A Conveyor Belt That Holds the World Awake
The Atlantic Meridional Overturning Circulation (AMOC) is a vast oceanic flow that moves warm surface water from the tropics toward the North Atlantic while pulling cooler water from the northern hemisphere southward. This immense system acts as a climate regulator for the planet. In centuries past, natural factors have slowed or even halted this conveyor belt, with profound global consequences. Most recently, evidence suggests AMOC is under threat from rising global temperatures, a shift that could reshape climate patterns around the world.
Researchers from Germany and Brazilian paleoclimatologist Cristiano Mazur Chiessi, a professor at the University of São Paulo, conducted the study and published their results in Nature Communications. Chiessi notes that a slowdown in AMOC would alter energy distribution across the globe, potentially triggering significant climatic changes.
This giant circulation moves warmer surface water from the South Atlantic toward the North Atlantic. There, this water releases heat to the cooler air above and also becomes denser, sinking to greater depths. The waters then travel southward, circling nearly the entire planet until they rise again near Antarctica, where they return to the surface, heat up, lose density, and complete the loop.
Atlantic currents do not just move water; they transport energy on a planetary scale. The South Atlantic Current carries roughly 18 million cubic meters of water every second and an enormous amount of energy—about 100,000 times the output of Itaipu, one of the world’s largest hydroelectric plants. The spatial distribution of this energy influences climates far and wide.
When AMOC remains strong and steady, global climate stays relatively balanced. A slowdown, however, redistributes energy and disrupts established climatological patterns across multiple regions.
It’s Already Happened Before
To understand potential future impacts, it helps to look to the past. During the last glacial period, AMOC episodes occurred several times between roughly 71,000 and 12,000 years ago. Marine sediment analyses from the coast of Venezuela to northeastern Brazil indicate that these slowdowns brought heavy rainfall to parts of northeastern Brazil while causing droughts in Venezuela and northern Amazonia. Similar precipitation shifts affected the tropics of North Africa and parts of Asia.
Researchers also found that warming at high northern latitudes led to a massive release of icebergs into the sea in areas around Canada and the United States. This influx of freshwater altered ocean salinity and density, driving changes in circulation that helped trigger an AMOC collapse. The high latitude sea floor warmed, releasing more icebergs as glaciers melted, further destabilizing the system.
Even today, the immense amount of freshwater from melting icebergs reshapes ocean chemistry in the North Atlantic, a region highly sensitive to AMOC dynamics. Changes here can ripple outward, influencing weather and climate globally.
What Happens When AMOC Slows Down
The process often begins with a seemingly modest weakening of AMOC, which can trigger warming at high northern latitudes and accelerate glacier melt. Meltwater reduces surface salinity and density, making surface waters less able to sink. As sinking slows, AMOC weakens further, setting off a feedback loop that could push the system toward a deeper, longer-term slowdown.
Recent observations show that AMOC has weakened in recent years. Three contributing factors are often cited: increased precipitation in the high latitudes of the North Atlantic, Greenland ice sheet melt, and broader surface warming from climate change. All three tie back to elevated greenhouse gas levels from human activity, underscoring the planetary stakes of this system.
Scientists warn that a sustained weakening could lead to unusual warming of the seafloor in northern latitudes, promoting more rapid glacier melting in Greenland. In a worst-case scenario, this could push AMOC toward collapse, amplifying climate disruption and intensifying the global climate crisis.
Reference work: marked citation to Nature Communications, 2022, Fig. 1. This study synthesizes paleoclimate data with modern observations to illuminate how AMOC responds to different forcing scenarios.
For further reading, researchers note the importance of monitoring AMOC as a critical indicator of climate system stability and potential tipping points in ocean circulation.