Ocean Science Explainer
A giant loop of ocean currents that regulates climate across the entire North Atlantic — and is showing signs of strain.
How AMOC Works — Schematic Cross-Section
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🌊 What is AMOC? A giant loop of ocean currents running the full length of the Atlantic. It carries warm water north near the surface and cold water south in the deep ocean — like a massive conveyor belt driven by temperature and salinity differences. |
🧂 What drives it? Cold, salty water is denser and sinks in the North Atlantic. This sinking pulls more warm, salty water northward behind it — the engine of the whole system. Oceanographers call this thermohaline circulation (thermo = heat, haline = salt). |
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🌍 Why does it matter? It keeps Northern Europe 5–10°C warmer than it would otherwise be. It moves carbon deep into the ocean, regulates rainfall across Africa and South America, and influences sea levels along the US East Coast. |
⚠️ Is it in trouble? Yes. Melting Greenland ice adds fresh, less-dense water that disrupts the sinking. Research shows AMOC has weakened and the IPCC says it is very likely to slow further through the 21st century. |
Warm water heads north
In the tropics, the sun heats surface water and evaporation makes it saltier. This warm, salty water flows northward — the Gulf Stream is the most famous part of this flow, transporting an enormous 17 million cubic meters of water per second.
Europe warms up
Along the way, the current releases heat into the atmosphere over the North Atlantic and Western Europe — giving the UK, Ireland, and Scandinavia a much milder climate than their high latitude would otherwise produce.
Water cools and sinks
Near Greenland and Iceland, the water loses its heat to cold Arctic air. Cold, salty water is dense — it sinks all the way to the ocean floor in a process called deep-water formation. This is the motor of the whole system.
Cold return flow heads south
The deep, cold water creeps southward along the ocean floor toward the Southern Ocean. It carries dissolved carbon dioxide with it, locking it away from the atmosphere and acting as a carbon sink.
Upwelling completes the loop
In tropical and Southern Ocean regions, the deep water is pushed back toward the surface (upwelling), warms again, and the cycle repeats. One full lap takes roughly 1,000 years.
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~1,000 yrs Weakest in at least the past millennium based on proxy records |
17 Sv Current transport in Sverdrups — projected to decline further this century |
Medium IPCC confidence that a full collapse can be avoided before 2100 |
Climate change is attacking AMOC from two sides: warmer water is less dense and sinks less readily, while melting Greenland ice adds a flood of fresh, lightweight water that suppresses the sinking entirely. The IPCC says a major slowdown is very likely — but a sudden complete collapse before 2100 is considered unlikely. If it did collapse, Europe could cool dramatically, US East Coast sea levels would rise sharply, and rainfall patterns across Africa and South America would be severely disrupted.
Sources: NOAA Ocean Service · Woods Hole Oceanographic Institution · UK Met Office · National Oceanography Centre (NOC) · IPCC Sixth Assessment Report (AR6), 2021