AMOC - The Atlantic Ocean Conveyor
The Atlantic Meridional Overturning Circulation carries warm water north and cold water south, moving heat that helps keep northwest Europe’s winters mild. It is one of the climate’s best-known tipping points, and whether it is slowing - and how close it might be to collapse - is one of the most debated questions in climate science. This page shows what the direct measurements say, how the conveyor works, and why studies reach such different answers.
Current State - 16.4 Sv, Below Average
Measured directly at 26.5°N to Mar 2024, the latest released data. The arrays publish in batches a year or more after collection, so this is the newest measurement available - not real time.
Atlantic Ocean
Warm water enters from the South Atlantic, runs up past Brazil and through the Caribbean, then crosses as the Gulf Stream and North Atlantic Current. Part circles south of Iceland and Greenland, the rest flows on as far as Fram Strait near 80°N. Cooling all the way, it sinks - mostly east of Greenland - and spills back south over the ridges as cold deep water. Meltwater from Greenland and the Arctic freshens those sinking regions, which makes the water lighter and slower to sink. Paths are schematic.
Latest Measurement - 12 Months to Mar 2024
16.4 Sv
-0.6 Sv against the 2004-2024 mean of 17.0 Sv. The subpolar OSNAP array averaged 15.3 Sv in its latest year of data (Jul 2022).
Trend Since Measurements Began
-1.5 Sv (-9%)
2019-2023 against 2005-2009. The overturning dipped sharply in 2009-10, partly recovered, and has run a little lower since - but it swings by several Sverdrups from year to year.
Is It Slowing?
Probably Weakening - No Collapse Under Way
The measurements show no collapse. Twenty years is too short to confirm a long-term trend, but sea-temperature fingerprints and older records point to weakening since the mid-20th century, and the IPCC judges further decline very likely this century. Whether it could tip, and when, is genuinely disputed.
Reading the Map
Warm water enters from the South Atlantic, runs up past Brazil and through the Caribbean, then crosses as the Gulf Stream and North Atlantic Current. Part circles south of Iceland and Greenland, the rest flows on as far as Fram Strait near 80°N. Cooling all the way, it sinks - mostly east of Greenland - and spills back south over the ridges as cold deep water. Meltwater from Greenland and the Arctic freshens those sinking regions, which makes the water lighter and slower to sink. Paths are schematic.
The Measurements
RAPID - The AMOC at 26.5°N
Moored instruments across the Atlantic from Florida to the coast of Africa have measured the overturning twice a day since Apr 2004. Monthly means to Mar 2024, the latest released data.
What Makes Up the 26.5°N Figure (record averages)
The overturning is what is left once the southward return flow in the upper ocean is taken off the northward Gulf Stream and wind-driven flow - roughly 32 + 4 − 18 ≈ 17 Sv heading north near the surface, balanced by deep water flowing south.
OSNAP - The Subpolar North Atlantic
A second array, from Canada to Greenland to Scotland, measures where the sinking happens. Monthly overturning from Aug 2014 to Jul 2022, the latest released data.
OSNAP’s headline result: most of the overturning happens east of Greenland, in the Irminger and Iceland basins, not in the Labrador Sea that models had long pointed to (Lozier et al. 2019). Each section is measured on its own density scale, so East and West do not simply add up to the whole-array figure.
How It Works
How the Great Ocean Conveyor Works
Why salt and cold make the Atlantic overturn - and why the flow can have two stable states.
1. Warm, Salty Water Heads North
The Gulf Stream and North Atlantic Current carry warm surface water from the tropics towards Europe and the Arctic. Evaporation on the way leaves it saltier.
2. It Cools and Sinks
In the far North Atlantic it gives up its heat to the air - which is part of why northwest Europe has mild winters - becomes cold and dense, and sinks kilometres deep, mostly east of Greenland.
3. Deep Water Flows South
That deep water spreads south through the Atlantic and on into the other oceans, while more surface water is drawn north to replace it - a slow loop that takes centuries to complete.
The weak spot is the sinking. If the northern water becomes fresher - from heavier rain, rivers and melting Greenland ice - it stays lighter and sinks less, so less warm water is pulled north and less salt arrives to keep it sinking. That self-reinforcing loop is why the AMOC is counted among the climate’s tipping elements. Wallace Broecker’s “conveyor belt” drawing made the idea famous (Broecker 1991), and Henry Stommel showed back in 1961, with just two boxes of water, that such a flow can have two stable states (Stommel 1961). Try his model below.
Stommel’s Two-Box Model
Model State
Strong overturning - the "on" state (today)
Strength +0.89
Push the slider past the tipping point and the flow collapses into the reversed state. Then pull it back: it stays “off” until the extra freshwater is removed altogether - right down to zero or just below. That memory is hysteresis, and it is why a collapse is feared - getting back is much harder than tipping over.
A simplified teaching model, so the numbers show relative strength rather than real ocean measurements, and it is not a forecast. Full climate models add winds, every ocean basin and the Southern Ocean, which is one reason they disagree about how close the real AMOC is to its tipping point - see the evidence below.
The AMOC and the AMV
The AMV is the North Atlantic’s slow warm and cool phases - a full warm-and-cool cycle takes about 60 to 80 years. The leading review finds strong evidence from observations and models that the AMOC’s slow swings are a crucial driver of it (Zhang et al. 2019), and in many models the overturning changes a few years before the sea surface follows. Not everyone agrees. One study argued the AMV can arise from the atmosphere alone (Clement et al. 2015), which others dispute (Zhang et al. 2016), and air pollution has played a part too (Booth et al. 2012). The link may also change as the circulation’s strength changes (Nature Communications 2026).
Twenty years of direct measurements is too short to settle it, since one AMV cycle is several times longer - so a match between the two over a few years is not proof on its own. The two run side by side in the 4byo Climate Symphony, and the NAO Tracker covers the AMV in detail.
Is It Slowing?
Is It Slowing? What the Evidence Says
Scientists reach different answers depending on the method - direct measurement, fingerprints in sea temperature, old records, statistics or climate models.
The overturning averaged 16.1 Sv in 2019-2023 against 17.7 Sv in 2005-2009. But it swings by several Sverdrups from year to year - it fell to its lowest in 2009-10 and partly recovered - so two decades of measurement are not yet long enough to separate a long-term decline from natural variation.
The cold patch south of Greenland and fast warming along the US east coast match a slowdown of about 15% (3 Sv) since the mid-20th century.
Caesar et al. 2018, NatureSeveral largely independent proxy records agree the 20th-century decline is unprecedented, leaving the AMOC at its weakest in over a millennium.
Caesar et al. 2021, Nature GeoscienceRebuilding the overturning from how much heat the North Atlantic gives up to the atmosphere finds no decline at 26.5°N from 1963 to 2017.
Terhaar et al. 2025, Nature CommunicationsRising variance and memory in a sea-temperature proxy point to a collapse around 2057, with a 95% range of 2025 to 2095. The assumptions behind it have been widely criticised.
Ditlevsen & Ditlevsen 2023, Nature CommunicationsA full climate model (CESM), pushed by slowly added freshwater until its AMOC tipped, yields a warning signal - the freshwater the AMOC carries at the southern edge of the Atlantic - and reanalysis data suggest the real ocean is on course to tip.
van Westen et al. 2024, Science AdvancesUnder extreme warming and freshwater forcing the AMOC weakens in every model but never fully collapses, held up by Southern Ocean winds - a collapse this century looks unlikely.
Baker et al. 2025, NatureThe AMOC will very likely decline over the 21st century. Medium confidence that the decline will not involve an abrupt collapse before 2100.
IPCC AR6 WG1, Chapter 9 (2021)More than 160 scientists judge the AMOC at risk of collapse below 2°C of global warming.
Global Tipping Points Report 2025Too Early to Tell?
For the measurements alone, yes. The direct record is about 20 years long, while the changes that matter play out over decades, so it cannot yet confirm or rule out a long-term decline. The disagreement elsewhere comes from method: the statistical warnings lean on long proxy records and assumptions that are hard to test, while most climate models have biases that may make their AMOC too stable. What almost all of the evidence agrees on is that a weaker AMOC is very likely as the world warms, and that a full collapse - unlikely this century on most estimates - would be a high-impact, hard-to-reverse event. That is why it is watched so closely.
If It Collapsed
If It Collapsed
What simulations and assessments say a shutdown would mean. These come from models deliberately pushed past the tipping point - they describe the stakes, not a forecast.
Europe
In a full climate model (CESM) pushed past its tipping point, Europe cooled by about 1°C per decade, over 3°C per decade in some regions, and European sea level rose by around 100 cm (van Westen et al. 2024) - all while the rest of the world kept warming.
Monsoons and Food
Much harsher northwest European winters, disrupted West African and Indian monsoons, and lower crop yields across much of the world, with major consequences for food security (Global Tipping Points Report 2025).
Carbon and Cascades
A collapse could flip the Southern Ocean from soaking up carbon to releasing it - 47 to 83 ppm of CO₂ over centuries, adding about 0.2°C of global warming - and above about 350 ppm of CO₂ (today it is around 430) the AMOC stays “off” once collapsed (PIK, 2026). One tipping point feeding another is what scientists call a cascade.
Explore
Explore Climate Data
Data Sources
Measuring Arrays
Twice-daily overturning since April 2004, shown here as monthly means. Moat et al., British Oceanographic Data Centre, doi:10.5285/48d0bf43-0598-ceb2-e063-7086abc062f1.
Data from the RAPID AMOC observing project is funded by the Natural Environment Research Council, U.S. National Science Foundation (NSF) with support from NOAA. They are freely available from https://rapid.ac.uk/.
Monthly overturning from August 2014, for the whole array and its eastern and western sections, doi:10.35090/gatech/78023.
OSNAP data were collected and made freely available by the OSNAP (Overturning in the Subpolar North Atlantic Program) project and all the national programs that contribute to it (www.o-snap.org).
Both arrays release data in batches a year or more after collection; this page updates automatically when a new release appears. Research findings are summarised from the papers linked in each card.
FAQs
AMOC - Common Questions
What is the AMOC?
The Atlantic Meridional Overturning Circulation (AMOC) is a system of ocean currents that carries warm, salty surface water north through the Atlantic and returns cold, deep water south. Often called the Great Ocean Conveyor, it moves heat towards Europe and the Arctic and helps keep northwest Europe's winters mild. The water sinks in the far North Atlantic, mostly east of Greenland, then spreads south at depth - a loop that takes centuries.
Is the AMOC the same as the Gulf Stream?
No. The Gulf Stream is a fast surface current driven largely by winds and the Earth's rotation, and it would keep flowing, though more weakly, even if the AMOC stopped. The AMOC is the much larger overturning loop - surface water heading north, sinking and returning south at depth. The Gulf Stream carries part of the AMOC's northward flow, which is why the two are often confused.
Is the AMOC collapsing?
There is no sign in the measurements that it is collapsing now. The RAPID array at 26.5°N shows the overturning a little weaker in recent years than when measurements began in 2004, but it varies by several Sverdrups from year to year and two decades is too short to separate a trend from natural swings. Studies disagree about the longer term: sea-temperature fingerprints and proxy records suggest it has weakened since the mid-20th century, a reconstruction from ocean heat loss finds no decline since the 1960s, and climate models range from steady weakening to tipping. The IPCC judges a decline this century very likely, with medium confidence that it will not collapse abruptly before 2100.
Why do scientists disagree about an AMOC collapse?
Mostly because of method. Statistical early-warning studies, such as Ditlevsen & Ditlevsen (2023), which estimated a collapse between 2025 and 2095, depend on long indirect records and assumptions that are hard to test, and have been widely criticised. Physics-based work in a full climate model (van Westen et al. 2024) found a warning signal suggesting the real ocean is on course to tip. But a comparison of 34 climate models (Baker et al. 2025) found the AMOC weakens without fully collapsing, held up by Southern Ocean winds - while many models may have an AMOC that is too stable. With only about 20 years of direct measurement, the data cannot yet settle it.
How is the AMOC measured?
Directly, with lines of moored instruments across the ocean. RAPID-MOCHA-WBTS has measured the overturning at 26.5°N, from Florida to the coast of Africa, twice a day since April 2004. OSNAP, from Canada via Greenland to Scotland, has measured the subpolar North Atlantic since 2014. Both release their data in batches, a year or more after collection, which is why this page is updated as new releases appear rather than monthly.
What is a Sverdrup?
A Sverdrup (Sv) is the oceanographers' unit of flow: one million cubic metres of water per second. The AMOC at 26.5°N averages about 17 Sv - around fifteen times the flow of all the world's rivers put together (about 1.2 Sv).
What would happen if the AMOC collapsed?
Simulations deliberately pushed past the tipping point show Europe cooling sharply even as the rest of the world warms - by about 1°C per decade, and more than 3°C per decade in some regions, in one full climate model (van Westen et al. 2024) - along with around 100 cm of extra European sea-level rise. The Global Tipping Points Report 2025 adds much harsher northwest European winters, disrupted West African and Indian monsoons and lower crop yields across much of the world. A 2026 PIK study found a collapse could turn the Southern Ocean from a carbon sink into a source, adding about 0.2°C of warming over centuries.
Could the AMOC recover after collapsing?
Not easily. The classic Stommel (1961) two-box model shows hysteresis: once the circulation flips to its "off" state, reducing the freshwater back below the tipping point is not enough - it only recovers once the extra freshwater is removed altogether. A 2026 PIK study found that at CO2 levels above about 350 ppm - well below today's roughly 430 ppm - a collapsed AMOC stays off. The interactive model on this page lets you try the hysteresis yourself.
Is the AMOC a tipping point?
Yes - it is one of the climate system's best-known tipping elements, because the sinking that drives it weakens itself once the northern water becomes fresh enough: less sinking draws less salty water north, which weakens the sinking further. The Global Tipping Points Report 2025 judges it at risk of collapse below 2°C of global warming. Whether, and when, the real ocean would pass that threshold is the open question.
How is the AMOC related to the NAO and the AMV?
The NAO is an atmospheric pressure pattern that changes week to week, while the AMOC is an ocean circulation that changes over decades. The NAO's winds help drive the heat loss and mixing where the AMOC's water sinks, and the AMOC is thought to be one of the influences behind the slow warm and cool phases of North Atlantic sea temperatures (the AMV). They are linked but distinct - see the NAO Tracker and the 4byo Climate Symphony.