What Is AMOC? What a Collapse Could Mean for Canada (Updated November 10, 2026)

Updated: November 10, 2026, 20:01 UTC

The Atlantic Meridional Overturning Circulation (AMOC) is a vast system of Atlantic currents that moves heat, salt and water between the tropics and the far North Atlantic. Canada’s 2026 climate assessment says human-caused warming is expected to gradually weaken it through the rest of this century. A sudden shutdown is a different, more severe possibility: it cannot be ruled out, but the assessment assigns medium confidence that the AMOC will not shut down before 2100.

For Canada, the distinction matters. Gradual weakening is projected to slightly reduce warming in eastern and northern Canada; a shutdown could produce a much stronger regional cooling influence and wider changes to climate patterns. Neither outcome means an immediate freeze or an end to the Gulf Stream. Environment and Climate Change Canada’s 2026 assessment says the evidence and models still leave important uncertainties.

Destaques

• AMOC is a connected Atlantic circulation, not one current or a climate “off switch.”
• Its gradual weakening this century is projected with high confidence; the scale and timing remain uncertain.
• A shutdown is not the expected 21st-century outcome, but scientists cannot rule it out.
• Canadian projections point to a modest reduction in warming in eastern and northern regions from weakening alone.

What is the AMOC, and how does it work?

AMOC stands for Atlantic Meridional Overturning Circulation. “Meridional” describes movement between the tropics and the poles; “overturning” refers to water moving both near the surface and at depth. Warm, relatively salty surface water flows north through the Atlantic. As it cools in northern regions, some becomes dense enough to sink and return southward at depth. The system also includes currents and mixing that connect these pathways.

Temperature and salt content both affect seawater density. Warming makes surface water less dense, while additional freshwater from rainfall, melting sea ice or Greenland ice can dilute it. If less water sinks in the North Atlantic, the overturning circulation can weaken. The AMOC is related to the Gulf Stream, but the terms are not interchangeable: winds also drive the Gulf Stream, and it would not simply vanish if the AMOC weakened or collapsed.

Is the AMOC already collapsing?

No confirmed shutdown has been reported. Direct, continuous AMOC observations are relatively recent, beginning in 2004 with the RAPID monitoring array near 26.5°N, so scientists cannot infer the full long-term history from direct measurements alone. The Canadian assessment finds high confidence that the circulation weakened and then partly recovered between 2004 and the present, but low confidence that those changes were caused by human activity. It also says historical climate simulations show no clear long-term decline.

That does not mean the future is stable. Canada’s assessment finds high confidence that the AMOC will gradually weaken over the remainder of the 21st century due to human influence. The IPCC Sixth Assessment Report likewise assessed a decline as very likely this century and judged, with medium confidence, that it would not involve an abrupt collapse before 2100. These assessments distinguish the direction of change, which is more certain, from the amount of weakening, which remains less certain.

What could an AMOC collapse mean for Canada?

A shutdown would disrupt a major route for moving heat northward, producing a stronger cooling influence around the subpolar North Atlantic than gradual weakening. Climate model experiments also indicate that a shutdown could alter rainfall patterns and shift tropical rain belts. These are conditional consequences of a hypothetical shutdown, not a forecast that it will happen or a description of current Canadian weather.

For eastern Canada, the federal assessment associates a weaker-than-normal AMOC with cooler and drier-than-normal winters. In one model experiment under a very high emissions scenario, weakening reduced projected warming by about 1°C in eastern and northern Canada from the 1961–1980 period to 2061–2080. Yet warming of more than 3°C across Canada still dominated in that experiment. The figures illustrate one model’s result, not a precise local forecast or the effect of a collapse.

Scientists’ confidence about a shutdown is limited partly because models do not capture every process affecting the circulation, including some ways Greenland meltwater could enter the ocean. Canada’s assessment notes that standard climate models do not simulate an AMOC shutdown this century, even under very high emissions, while also cautioning that such an outcome cannot be ruled out. Past abrupt changes in ocean circulation show that large shifts have occurred in Earth’s history, but they do not establish when or whether one will occur again.

What happens next in AMOC research?

Researchers continue to combine direct measurements, ocean observations, climate models and evidence from past climates. Longer records can help separate short-term natural variation from a sustained trend, while improved models may better represent the effects of freshwater and changing ice sheets. For readers, the practical takeaway is to track assessments that clearly distinguish a projected gradual weakening from the less certain shutdown scenario.

Frequently asked questions

Would an AMOC collapse stop the Gulf Stream?

No. The Gulf Stream would not simply disappear; it is partly driven by winds as well as by the wider Atlantic circulation.

Does AMOC weakening mean Canada will get colder?

Not overall. Weakening is projected to slightly reduce warming in eastern and northern Canada, while the country is still expected to warm.

Is an AMOC shutdown expected before 2100?

Current assessments do not treat a shutdown before 2100 as the expected outcome, but uncertainty means it cannot be ruled out.