The Atlantic meridional overturning circulation (AMOC) is the main ocean current system in the Atlantic Ocean. It is part of Earth's ocean circulation system and helps regulate the planet's climate. The AMOC includes surface and deep ocean currents that are influenced by changes in weather, temperature, and salt levels. These currents make up half of the global thermohaline circulation, with the other half being the Southern Ocean overturning circulation.
The AMOC consists of a northward movement of warm, salty water in the upper layers of the Atlantic and a southward movement of cold, less salty water in the deep ocean. Warm water from the southern regions becomes saltier because of high evaporation rates in tropical areas. This salty water forms the upper layer of the ocean, but when it cools, its increased density causes it to sink into the deep. This sinking process is a key part of how the AMOC works. The system connects through overturning areas in the Nordic Seas and the Southern Ocean. These regions are important for exchanging heat, oxygen, carbon, and nutrients, which support ocean ecosystems and the ocean's role in storing carbon. Changes in the strength of the AMOC can affect many parts of the climate system.
Climate change may weaken the AMOC by increasing ocean heat and adding more freshwater from melting ice sheets. Studies suggest that by 2015, the AMOC was weaker than it was before the Industrial Revolution. Scientists are still debating whether this weakening is due to climate change or natural changes over time. Models predict the AMOC will weaken further during the 21st century. This weakening could lower average air temperatures in Scandinavia, Great Britain, and Ireland, as these regions rely on the North Atlantic Current for warmth. It could also speed up sea level rise near North America and reduce the growth of marine life in the North Atlantic.
If the AMOC weakens severely, the circulation might collapse. Such a collapse would be hard to reverse and could act as a tipping point in the climate system. A collapse would cause much lower temperatures and less rainfall in Europe. It might also increase extreme weather events and lead to other serious consequences.
Overall structure
The Atlantic meridional overturning circulation (AMOC) is the main current system in the Atlantic Ocean and is part of the global thermohaline circulation, which connects the world's oceans through a continuous "conveyor belt" of water movement. Normally, warmer, less-salty water stays near the ocean's surface, while deeper water is colder, saltier, and denser, a process called ocean stratification. Over time, deep water gains heat or loses salt through mixing with the surface layer, becoming less dense and rising. Differences in temperature and salinity between ocean layers and regions drive the thermohaline circulation. The Pacific Ocean has less salt than other oceans because it receives large amounts of rainfall. Its surface water is not salty enough to sink below several hundred meters, so deep ocean water must come from other areas.
In the North Atlantic, ocean water is saltier than in the Pacific. This happens partly because evaporation on the surface leaves salt behind and partly because sea ice near the Arctic releases salt as it freezes. Also, moisture evaporated from the Atlantic is carried by wind across Central America to the eastern North Pacific, where it falls as rain. Major mountain ranges like the Tibetan Plateau, Rocky Mountains, and Andes block moisture from returning to the Atlantic.
Because of this, Atlantic surface water becomes salty and dense, eventually sinking to form the North Atlantic Deep Water (NADW). NADW forms mainly in the Nordic Seas, where different water masses, such as the Denmark Strait Overflow Water (DSOW), Iceland-Scotland Overflow Water (ISOW), and Nordic Seas Overflow Water, mix. Labrador Sea Water may also play a role, but recent evidence suggests water from the Labrador and Irminger Seas mostly circulates within the North Atlantic Gyre and has limited connection to the rest of the AMOC.
NADW is not the deepest layer in the Atlantic Ocean. The Antarctic Bottom Water (AABW) is the densest and deepest layer in any ocean basin deeper than 4,000 meters (2.5 miles). As AABW rises, it merges with NADW, strengthening it. The formation of NADW starts the lower part of the circulation. The sinking of water that creates NADW is balanced by an equal amount of rising water. In the western Atlantic, wind-driven ocean mixing, called Ekman transport, causes strong upwelling in the Canary Current and Benguela Current, which flow along the northwest and southwest coasts of Africa. As of 2014, upwelling near the Canary Current is stronger than near the Benguela Current, though the opposite was true before the Central American Seaway closed during the late Pliocene. In the Eastern Atlantic, upwelling occurs only during certain months because this region's deep thermocline makes it more dependent on sea surface temperature than wind. A multi-year upwelling cycle also aligns with the El Niño/La Niña cycle.
Meanwhile, NADW moves southward and upwells in the Southern Ocean near Antarctica, connecting it to the Southern Ocean overturning circulation (SOOC). After upwelling, water near Antarctica is cooled by sea ice and sinks again, rejoining the lower part of the circulation. Some of this water becomes part of AABW, while other water flows into the Pacific and Indian Oceans. Water that upwells at lower, ice-free latitudes moves northward due to Ekman transport and enters the upper part of the circulation. Warm water in the upper part returns to the North Atlantic mainly near Africa and through the Indonesian archipelago. Once this water reaches the North Atlantic, it cools and becomes denser, sinking again to feed into NADW.
Role in the climate system
Equatorial areas are the hottest part of the globe. Heat from these areas moves toward the poles because of the way heat moves. Most of this heat is carried by wind patterns in the atmosphere, but warm ocean currents also help. Heat from the equator moves either north or south. In the Atlantic Ocean, the heat flow is mainly northward. Much of the heat movement in the Atlantic happens because of the Gulf Stream, a surface current that carries warm water north from the Caribbean. The Gulf Stream is mainly driven by wind, but its northern part, the North Atlantic Current, gets heat from the Atlantic Meridional Overturning Circulation (AMOC). This circulation helps move up to 25% of the total heat toward the northern hemisphere and affects the climate in northwest Europe.
Atmospheric patterns also help move heat. Without ocean currents, the climate in northern Europe might be as cold as northern North America, possibly 15–20 °C (27–36 °F) colder. However, this idea is not widely accepted. Some studies suggest that if the AMOC collapsed, it could cause cooling similar to an ice age, but the accuracy of these results is uncertain. Scientists agree that the AMOC keeps northern and western Europe warmer than it would be otherwise. The temperature difference varies by area, from 4 °C (7.2 °F) to 10 °C (18 °F). For example, studies show the Gulf Stream was weaker between 1200 and 1850, which may have contributed to a period called the Little Ice Age.
The AMOC helps the Atlantic Ocean absorb more carbon in two ways. First, rising water from the deep ocean brings nutrients to the surface, supporting the growth of phytoplankton and increasing the amount of photosynthesis in surface waters. Second, upwelled water has low carbon levels because it is old and has not absorbed recent human-made carbon dioxide. This water absorbs more carbon than surface water and prevents it from returning to the atmosphere when it sinks. While the Southern Ocean is the strongest carbon sink, the North Atlantic is the largest single carbon sink in the northern hemisphere.
The AMOC is not static. It changes over time due to interactions between water layers of different temperatures and salt levels. These changes include small, repeating patterns and larger, long-term shifts. Many of these shifts happened during the Late Pleistocene, which was the last major ice age before the current warm period. This time included the Last Glacial Period, known as the "last ice age." During this time, there were 25 sudden temperature changes between the hemispheres, called Dansgaard–Oeschger events (D-O events). These events were discovered by scientists studying Greenland ice cores in the 1980s.
D-O events are best known for rapid warming in Greenland, with temperatures rising by 8–15 °C (15–27 °F) over decades. Similar warming happened across the North Atlantic, but the Southern Ocean cooled during these events. This pattern matches the AMOC moving more heat between hemispheres. Warming in the northern hemisphere likely caused ice sheets to melt, and many D-O events ended when large icebergs broke off from the Laurentide ice sheet. As these icebergs melted, the ocean became fresher, weakening the AMOC and stopping the warming.
Scientists do not fully agree on why the AMOC changed so much during the ice age. Some ideas include changes in salt levels in the North Atlantic or wind patterns affected by ice sheet growth and shrinkage. Research from the 2010s suggests the AMOC was most sensitive to changes during periods with large ice sheets and low carbon dioxide levels, making the Last Glacial Period a key time for these events. Evidence suggests warming in the southern hemisphere may have started the D-O events, as warmer water moved north through ocean currents. However, it is unclear whether the AMOC changed first or responded to other changes, such as shifts in sea ice.
D-O events are numbered in reverse order, with the oldest events having the highest numbers. The last major event, D-O event 1, happened about 14,690 years ago. It marked the end of the Oldest Dryas period and the start of the Bølling–Allerød Interstadial, a warm period that lasted until about 12,890 years ago. This event was named after two sites in Denmark where plant fossils showed the climate was warm. The warming in the northern hemisphere was balanced by cooling in the southern hemisphere, with little overall change in global temperatures. This matches changes in the AMOC. The warm period also caused a rise in sea levels, called Meltwater pulse 1A, due to ice sheets melting.
The Bølling and Allerød stages were separated by a short period of cooling in the northern hemisphere and warming in the southern hemisphere, known as the Older Dryas. This period was named after a plant that grew during colder times. The warm interglacial period ended with the Younger Dryas (YD) period, from 12,800 to 11,700 years ago, when northern hemisphere temperatures dropped to near-glacial levels. This happened because the AMOC slowed down, likely due to fresh water from melting ice in the Laurentide ice sheet. Unlike true ice age events, this change was caused by a large flow of meltwater from the Mackenzie River in Canada. During the Younger Dryas, rainfall patterns shifted, causing more rain in North America and less in South America and Europe. Global temperatures changed little during this time, and warming resumed after it ended.
Stability and vulnerability
The AMOC did not always exist. For most of Earth's history, ocean current movement in the northern hemisphere happened in the North Pacific. Evidence from Earth's past shows that the shift of these ocean currents from the Pacific to the Atlantic occurred 34 million years ago during the Eocene-Oligocene transition, when the Arctic-Atlantic gateway had closed. This closure changed the structure of ocean currents driven by temperature and salt differences. Some researchers suggest that climate change might eventually reverse this shift and restore the Pacific circulation if the AMOC stops. Climate change affects the AMOC by making surface water warmer due to Earth's energy imbalance and by making surface water less salty because of large amounts of fresh water from melting ice, mainly from Greenland, and increased rain in the North Atlantic. These changes would increase the difference between surface and deep water layers, making the upwelling and downwelling that drive the circulation harder to maintain.
In the 1960s, Henry Stommel studied the AMOC and developed the Stommel Box model, which introduced the idea of Stommel Bifurcation. This concept suggests the AMOC can exist in either a strong state, like the one observed in history, or a weak state that might not recover unless warming and freshening are reduced. Warming and freshening could directly cause the AMOC to weaken or collapse, or its normal fluctuations might push it past a critical point. The possibility that the AMOC is a bistable system, meaning it is either "on" or "off," and could suddenly collapse has been discussed by scientists since Stommel's work.
Some models developed after Stommel's research suggest the AMOC could have one or more stable states between full strength and full collapse. These are more common in Earth Models of Intermediate Complexity (EMICs), which focus on parts of the climate system like the AMOC and ignore others, compared to general circulation models (GCMs), which are more comprehensive but often simplify interactions. GCMs usually show the AMOC has a single stable state and is unlikely to collapse. Researchers have noted that GCMs may appear more stable because they redirect large amounts of fresh water toward the North Pole, where it does not affect the circulation, a process not seen in nature.
In 2024, three researchers used a Community Earth System Model (CIMP) to simulate a classic AMOC collapse, similar to what happens in EMICs. Unlike some other simulations, they gradually increased fresh water input over 1,700 years before the collapse occurred. Their simulation reached fresh water levels equivalent to a sea level rise of 6 cm (2.4 in) per year, about 20 times higher than the 2.9 mm (0.11 in)/year rise between 1993 and 2017. The researchers said these extreme conditions were used to balance the model's unrealistic stability, and the results should not be seen as predictions but as detailed representations of how currents might change before collapse. Other scientists agreed the study would help improve future research once better data is available.
Some research suggests EMICs may overestimate the risk of AMOC collapse because they apply a constant flow of fresh water to the circulation. In one study, using variable fresh water levels instead of constant ones delayed the collapse by over 1,000 years in a typical EMIC model. This simulation matched reconstructions of the AMOC's response to a major fresh water event 13,500–14,700 years ago. A 2022 study found limited effects from massive fresh water input during the final stage of the Holocene deglaciation, when sea levels rose about 50 meters (160 feet). It suggested many models overestimate the impact of fresh water on the AMOC. If the AMOC depends more on wind strength, which changes little with warming, it might be more resistant to collapse. Some researchers believe the less-studied Southern Ocean overturning circulation (SOOC) may be more vulnerable to collapse than the AMOC.
High-quality Earth system models suggest AMOC collapse is unlikely unless warming of at least 4°C (7.2°F) continues long after 2100. Some paleoceanographic research supports this idea. Some scientists worry that complex models may be too stable and that simpler models predicting an earlier collapse are more accurate. One simpler model suggests AMOC collapse could occur around 2065 (updated from 2057 in August 2025), though many scientists are skeptical. Some research also suggests the SOOC may be more prone to collapse than the AMOC. In October 2024, 44 climate scientists published an open letter stating that recent studies suggest the risk of AMOC collapse has been greatly underestimated and that it could happen in the next few decades, with severe effects for Nordic countries. They urged Nordic countries to follow the Paris Agreement to prevent this outcome.
Trends
Before 2024, scientists had different opinions about the Atlantic Meridional Overturning Circulation (AMOC). Observations showed the AMOC was slowing down, but climate models suggested it remained stable. In November 2024, a study published in Nature Geoscience aimed to resolve this issue. Scientists used models that study Earth's systems and ocean movements, including ocean and sea ice. After this study, observations and models matched more closely. The research found the AMOC slowed by 0.46 sverdrups per decade since 1950.
Direct measurements of the AMOC’s strength began in 2004 through the RAPID project, which uses a network of instruments at 26°N in the Atlantic. Observational data must be collected over long periods to be useful. Some scientists used smaller-scale data to make predictions. For example, in 2005, research by Peter Wadhams found that water movement in the Greenland Sea, part of the AMOC, was less than a quarter of its normal strength. In 2000, other scientists studied the North Atlantic Gyre (NAG), also called the Northern Subpolar Gyre (SPG). Measurements in 2004 showed a 30% decline in the NAG compared to 1992, but later RAPID data showed this was a statistical anomaly. Observations from 2007 and 2008 revealed the NAG had recovered. It is now known the NAG operates separately from the rest of the AMOC and could collapse independently.
By 2014, enough RAPID data had been processed up to 2012. These data showed a decline in AMOC circulation 10 times greater than predicted by models at the time. Scientists debated whether this decline was due to climate change or natural long-term changes in the circulation. Data up to 2017 showed the decline in 2008–2009 was unusually large, but circulation after 2008 was weaker than in 2004–2008.
The AMOC is also measured by tracking heat transport, which is linked to ocean currents. In 2017 and 2019, estimates from NASA’s CERES satellites and Argo floats suggested 15–20% less heat transport than RAPID data indicated. These findings suggested a stable AMOC with limited signs of long-term changes.
Measurements of the Florida Current, which is part of the AMOC, have shown stability over the last 40 years after adjusting for changes in Earth’s magnetic field.
Climate reconstructions use historical data to study the AMOC’s past state, though these methods are less reliable than direct observations. In February 2021, RAPID data was combined with reconstructions from data collected 25 years earlier. This study found no overall decline in the AMOC over the past 30 years. A 2020 study in Science Advances found no significant change in AMOC circulation compared to the 1990s, though changes occurred in other parts of the North Atlantic. A 2022 review noted that while global warming may weaken the AMOC over time, detecting changes since 1980 is difficult because the data show both weakening and strengthening periods. The review called for more sensitive, long-term research.
Some reconstructions compared the current AMOC to its state a century ago. A 2010 study found the AMOC has weakened since the late 1930s, with a major shift in ocean circulation around 1970. A 2015 study linked a cooling pattern in temperature records to a 15–20% weakening of the AMOC over 200 years. Between 1975 and 1995, the AMOC was weaker than at any time in the past millennium. A 2018 study suggested a 15% weakening since the mid-20th century. A 2021 reconstruction used over a century of ocean data and showed significant changes in eight AMOC indicators, suggesting "almost complete loss of stability." However, this study excluded data from 35 years before 1900 and after 1980 to maintain consistency. A 2022 study using data from 1900 to 2019 found no change in the AMOC between 1900 and 1980, with a small reduction in strength starting in 1980, which fits within natural variability.
Sediment analyses showed the AMOC weakened by 20% from the middle of the 20th century. A 2018 study noted the AMOC has been unusually weak compared to the previous 1,500 years, suggesting human activity may have influenced the timing of its decline after the Little Ice Age. A 2017 review found strong evidence of past AMOC changes during abrupt climate events like the Younger Dryas and Heinrich events. A 2022 reconstruction found the Atlantic’s long-term climate patterns are showing increased "memory," meaning they are less likely to return to normal states. This could indicate a slow, unnoticed loss of AMOC stability not seen in most models.
In February 2021, a major study in Nature Geoscience reported the AMOC weakened significantly over the past millennium, suggesting human actions caused the change. The study’s co-author stated the AMOC had already slowed by 15% and predicted further weakening in 20–30 years, which could lead to more storms and heatwaves in Europe and rising sea levels on the U.S. East Coast. In February 2022, a "Matters Arising" commentary in Nature Geoscience, co-authored by 17 scientists, challenged these findings, saying the long-term AMOC trend remains uncertain. The 2021 study’s authors defended their conclusions.
Some scientists link recent climate changes to AMOC
Projections
In the past, CMIP models, which are the most trusted tools in climate science, have shown that the Atlantic Meridional Overturning Circulation (AMOC) is very stable. Even if it weakens, it usually recovers rather than collapsing completely. For example, in a 2014 experiment where carbon dioxide (CO₂) levels were doubled quickly from 1990 levels and then stayed the same, the AMOC weakened by about 25% but did not collapse. It recovered slightly—by about 6%—over the next 1,000 years. In 2020, research estimated that if global warming stops at 1.5°C, 2°C, or 3°C by 2100, the AMOC would weaken for 5–10 years after warming stops but would not collapse. It would recover somewhat after about 150 years. Many scientists believe that models avoid predicting collapse because they have errors that affect their accuracy.
Although CMIP models have improved over time, the sixth generation of models, called CMIP6, still has some inaccuracies. On average, these models show greater weakening of the AMOC in response to greenhouse gas warming compared to earlier models. For example, when four CMIP6 models simulated the AMOC under a scenario where CO₂ levels more than double by 2100, they predicted a decline of over 50% by 2100. These models also struggle to accurately simulate the North Atlantic Deep Water (NADW), which affects confidence in their predictions.
To improve accuracy, scientists have tested bias correction in models. In one experiment, applying bias correction to a model caused the AMOC to collapse after 300 years in a CO₂ doubling scenario. In 2016, a study combined results from eight CMIP5 models with better estimates of Greenland ice melt. It found that under a moderate warming scenario (RCP 4.5), the AMOC would weaken by about 18% by 2100, and under a high-warming scenario (RCP 8.5), it would weaken by 37%. If these scenarios continued past 2100, the AMOC stabilized under RCP 4.5 but continued to weaken under RCP 8.5, leading to a 74% decline by 2290–2300 and a 44% chance of complete collapse. In 2020, another study used a more advanced model and found similar results under RCP 4.5, but under RCP 8.5, the AMOC declined by two-thirds after 2100 without collapsing.
In 2023, a study using data from several models suggested that the AMOC might collapse around 2065, with a 95% chance of collapse between 2037 and 2109. This study received attention and criticism because the models used are less reliable and may confuse a slowdown with a complete collapse. The study used temperature data from a specific ocean region, which some scientists say does not represent the entire AMOC. Others called the research "worrisome" but noted it could help once better data is available. Experts agreed the data used was not strong enough to support the findings.
In 2025, a study extended CMIP6 simulations beyond 2100 and tracked the deep northern overturning cell, which is linked to NADW. Under a high-emissions scenario (SSP5-8.5), all nine models showed the AMOC weakening from about 14–26 Sv to 1–6 Sv by 2100. The models also showed a shift in deep ocean currents, with a collapse of deep winter convection in subpolar regions happening about 30 years before the AMOC shutdown. This was linked to feedbacks that destabilize the overturning. The models also showed a shallow, wind-driven current remained after the AMOC weakened.
Large review papers and reports can evaluate model results, observations, and historical data to provide expert opinions. In 2001, the IPCC Third Assessment Report said the AMOC would likely weaken but not stop, with warming effects outweighing cooling. In 2014, the IPCC Fifth Assessment Report said a rapid transition of the AMOC was "very unlikely." In 2021, the IPCC Sixth Assessment Report said the AMOC is "very likely" to weaken this century and that changes could be reversed if warming stops. However, confidence in avoiding collapse before 2100 was reduced to "medium" due to studies showing model biases and simpler models suggesting the AMOC might be more vulnerable.
The IPCC Sixth Assessment Report summarized that the AMOC is very likely to weaken this century but that a sudden collapse is not expected before 2100. If a collapse were to happen, it would likely cause sudden changes in weather patterns, water cycles, and ecosystems. In 2022, a study identified 16 possible climate tipping points, including an AMOC collapse. It estimated that collapse would most likely occur with 4°C of warming but could happen between 1.4°C and 8°C. Once triggered, collapse might take 15–300 years, with the most likely time being about 50 years. The collapse of the Northern Subpolar Gyre was also identified as a separate tipping point, possibly triggered at 1.8°C. This collapse could lower global temperatures by 0.5°C and European temperatures by 3°C, with major effects on precipitation.
A report on the state of the cryosphere (ice-covered regions) said the AMOC may be heading toward collapse due to ice melt and warming water. This could cause Northern Europe to cool rapidly—by more than 3°C per decade—with no realistic way to adapt. At the same time, other regions might experience extreme weather changes.
Effects of AMOC slowdown
As of 2024, scientists do not agree on whether the AMOC has been slowing down steadily. However, most experts believe that if climate change continues, the AMOC will likely slow down in the future. According to the IPCC, the most likely effects of a weaker AMOC include less rain in the middle parts of the world, more intense rain in tropical and European regions, and stronger storms that travel along the North Atlantic. A 2020 study found that a weaker AMOC could slow the loss of Arctic sea ice and create weather patterns similar to those during the Younger Dryas, such as the Intertropical Convergence Zone moving farther south. Rainfall changes would be much greater in situations with high emissions.
A weaker AMOC would cause sea levels to rise faster along the U.S. East Coast. At least one event linked to a temporary slowdown of the AMOC has already been recorded. This effect would happen because warmer water near the coast would expand more, trapping more heat in coastal areas and reducing the amount of heat sent toward Europe. This is why sea level rise along the U.S. East Coast is expected to be three to four times higher than the global average.
Some scientists think a partial slowdown of the AMOC could cool Europe by about 1°C (1.8°F). Other areas would be affected differently. A 2022 study found that winters in Siberia were milder in the 20th century when the AMOC was weaker. One analysis suggested that a slower AMOC might lower the social cost of carbon, a measure of climate change’s economic effects, by −1.4%. This is because Europe contributes more to the global economy than regions harmed by the slowdown. However, this study may have underestimated the overall climate impacts. Some research argues that a slower AMOC would reduce the ocean’s ability to absorb heat, increasing global warming, though this view is not widely shared.
A 2021 study said other major climate tipping points, such as the Greenland ice sheet, the West Antarctic Ice Sheet, and the Amazon rainforest, are connected to the AMOC. The study noted that changes to the AMOC alone are unlikely to cause tipping in other systems. However, a slower AMOC could link these systems together, lowering the global-warming threshold at which tipping points might occur. This connection could lead to a chain reaction of tipping events over several centuries.
Effects of an AMOC shutdown
If the AMOC completely collapses, it may be hard to fix. Recovery could take thousands of years. A shutdown of the AMOC is expected to cause large drops in temperature in Europe, especially in Britain and Ireland, France, and the Nordic countries. In 2002, research compared AMOC shutdown to Dansgaard–Oeschger events—sudden temperature changes during the Last Glacial Period. That study suggested Europe could cool by up to 8 °C (14 °F). In 2022, a major review of tipping points concluded an AMOC collapse would lower global temperatures by about 0.5 °C (0.90 °F), while temperatures in Europe could fall by 4 °C (7.2 °F) to 10 °C (18 °F).
A 2020 study looked at how an AMOC collapse might affect farming and food production in Great Britain. It found that, after accounting for warming effects, temperatures in Britain could drop by an average of 3.4 °C (6.1 °F). Rainfall during the growing season could decrease by about 123 mm (4.8 in), reducing suitable farmland from 32% to 7%. This could lower the value of British farming by about £346 million each year—over 10% of its 2020 value.
In 2024, a study modeled an AMOC collapse in a pre-industrial world and predicted even greater cooling in Europe. It suggested sea surface temperatures in northwest Europe could drop by 10 °C (18 °F), and February temperatures on land could fall by 10 °C (18 °F) to 30 °C (54 °F) in northern and western Europe within a century. This could lead to sea ice extending into the territorial waters of the British Isles and Denmark during winter, while Antarctic sea ice would shrink. These findings do not include the warming effects of climate change, and the study’s methods are debated.
A 2015 study led by James Hansen found that a shutdown or slowdown of the AMOC could increase severe weather. This is because it strengthens wind patterns, which might lead to more frequent and intense winter storms with strong winds and heavy snowfall. This paper is also debated.
Several studies have examined how an AMOC collapse might affect the El Niño–Southern Oscillation (ENSO). Results vary, ranging from no major impact to stronger ENSO events, more frequent La Niña conditions, and changes in rainfall and drought patterns in parts of Australia and the southwestern U.S.
A 2021 study used a simplified model to explore how an AMOC collapse might affect the Amazon rainforest. It suggested that increased rainfall in the southern Amazon could help prevent the rainforest from shrinking and becoming a savanna. A 2024 study found that the Amazon’s seasonal rainfall patterns could reverse, with dry seasons becoming wet and wet seasons becoming dry.
A 2005 paper stated that a severe disruption of the AMOC could reduce North Atlantic plankton populations to less than half their usual levels due to changes in ocean layer mixing and nutrient availability. A 2015 study simulated ocean changes under AMOC slowdown or collapse scenarios and found that dissolved oxygen levels in the North Atlantic would drop significantly, though oxygen levels in other parts of the world might rise slightly.