How we track the Atlantic overturning circulation

What the dashboard shows, where the numbers come from, and what they can’t tell you.

The short answer

The Atlantic overturning circulation (AMOC for short, “the conveyor” on the dashboard) carries warm surface water north. In the far North Atlantic that water gives off its heat, becomes denser, sinks, and flows back south deep below the surface. It is not the Gulf Stream. The Gulf Stream is driven mainly by wind and will not switch off. The overturning is driven by differences in temperature and saltiness, which is why a warmer, fresher North Atlantic can weaken it.

It has weakened. Direct measurements across the Atlantic began in 2004. In the first five years the overturning moved about 18.4 million cubic metres of water per second; since 2009 it has averaged about 15.5. (Oceanographers call a million cubic metres per second a sverdrup, Sv, and the dashboard uses that unit.) The flow swings a lot from year to year. 2022, the latest year published, was the strongest since 2007, so no single year settles anything.

The UN’s climate science panel, the IPCC, judged in 2021 that the overturning will very likely weaken further this century, and that a collapse before 2100 is unlikely but cannot be ruled out. Several studies published since then argue the risk is higher than that.

How we know

Direct measurement at 26°N (RAPID). Since 2004, a line of moorings across the Atlantic, from Florida and the Bahamas to the coast of Africa, has recorded temperature, saltiness, pressure and currents from the surface to the seafloor. From those readings, the UK–US RAPID programme calculates how much water the overturning moves. It is the longest continuous direct record of the AMOC, and it is the series in the dashboard’s main chart.

Farther north (OSNAP). Since 2014, a second array called OSNAP has measured the overturning between Canada, Greenland and Scotland, where the sinking actually happens. It sees a different part of the same circulation, so its numbers are not directly comparable with RAPID’s. The dashboard shows its 2014–2020 average as context.

Indirect evidence (the “cold blob”). Over the past century almost the whole planet has warmed, but a patch of ocean south of Greenland has warmed far less, and at times cooled. Many scientists read that as a sign that less heat is being carried north. It is a fingerprint, not a measurement of flow: winds and the exchange of heat with the air affect it too. The dashboard tracks it with NOAA’s Atlantic Multidecadal Variability index, a record of North Atlantic sea-surface temperature back to 1856. The coloured patch on the dashboard is a diagram drawn from that index, not a satellite map.

How current each part is

Overturning at 26°N (RAPID): 2004–2022. New years arrive in published releases from the British Oceanographic Data Centre, usually a few years after they are measured, and we add each release by hand. That is why the chart stops at 2022.
Subpolar overturning (OSNAP): the 2014–2020 average from the published results. We update it when the team publishes new ones.
Sea-surface temperature index (NOAA): NOAA has not updated this series since January 2023 and it is no longer maintained. We keep the whole record back to 1856 and still check it every night. A maintained sea-surface temperature record will be added: where the two overlap, it serves as an independent check on this one, and it carries the index forward from 2023.
Recent research list: checked every night against OpenAlex, an open catalogue of scholarly papers. Only articles in peer-reviewed journals are listed.

Where scientists disagree

The question is less whether the overturning can weaken than how fast, and whether it could pass a point beyond which it does not recover. The papers marked on the dashboard’s chart take different positions:

Caesar and colleagues (2018) used the cold-blob fingerprint to estimate that the overturning has weakened by about 15% since the mid-twentieth century.
Ditlevsen and Ditlevsen (2023) found statistical warning signs in the same kind of temperature record and estimated that a collapse could come as early as mid-century. Other researchers question the method.
van Westen and colleagues (2024) produced a collapse in a detailed climate model and identified a warning sign that can be measured in the real ocean, which they argue shows the overturning heading toward a tipping point.
Rahmstorf (2024) reviewed the evidence and concluded that the weakening is real and the risk of tipping this century is substantial.
In October 2024, 44 climate scientists wrote to the Nordic Council of Ministers that the risk of collapse has been greatly underestimated.
Baker and colleagues (2025) pushed 34 climate models to extremes and found the overturning weakens but does not fully collapse this century, because winds over the Southern Ocean keep driving part of it.
Portmann and colleagues (2026) corrected climate models against observations and projected a weakening of about half by 2100 under a middle emissions scenario, more than the models’ average.

The IPCC’s 2021 assessment came before most of this work, so its next report will be the first to weigh it.

What the dashboard can’t tell you

It cannot tell you that a collapse is coming. Eighteen years of direct measurement are invaluable but short for a circulation that varies over decades. Anything before 2004 relies on indirect evidence, such as ocean sediments and temperature fingerprints, with wider uncertainty. A decline since 2004 shows weakening over that period. It is not a countdown.

It cannot forecast your local weather either. A weaker overturning could make winters in parts of northwest Europe colder than they would otherwise be, shift tropical rain belts, and raise sea level along parts of the US East Coast. How much, when and where depends on emissions, melting ice, winds and the climate models used. The “near you” section describes the kinds of effects expected in your region, not a forecast for your town.

Credits

The direct record exists because the RAPID and OSNAP teams have kept instruments in the open Atlantic for years, and the British Oceanographic Data Centre publishes their data. The sea-surface temperature index comes from NOAA’s Physical Sciences Laboratory, and the research list from OpenAlex. This dashboard collects and presents their work.

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