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 plays a key role in the climate system. The AMOC includes surface and deep ocean currents in the Atlantic 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 south becomes saltier because of high evaporation rates in tropical areas. This salty water forms the upper layer of the ocean, but when it cools, it becomes denser and sinks. This sinking process is a key part of how the AMOC works. Overturning occurs in specific regions, such as the Nordic Seas and the Southern Ocean. These areas are important for the exchange of heat, oxygen, carbon, and other nutrients, which support ocean ecosystems and help the ocean store 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. Studies suggest that the AMOC has been weaker since 2015 than it was before the Industrial Revolution. Scientists are still discussing how much of this weakening is due to climate change and how much is part of the ocean's natural changes over time. Climate models predict the AMOC will continue to weaken during the 21st century. This weakening could lower average air temperatures in Scandinavia, Great Britain, and Ireland because these regions rely on the North Atlantic Current for warmth. It could also increase sea level rise near North America and reduce the growth of marine life in the North Atlantic.
If the AMOC weakens severely, the circulation could collapse. A collapse would be difficult to reverse and is considered a major tipping point in the climate system. This collapse could lead to much colder temperatures and less rainfall and snowfall in Europe. It might also increase the number of extreme weather events and cause other serious effects.
Overall structure
The Atlantic meridional overturning circulation (AMOC) is the main current system in the Atlantic Ocean. It is part of the global thermohaline circulation, which connects all the world’s oceans through a continuous "conveyor belt" of water movement. Normally, warm, less-saline water stays near the ocean’s surface, while deeper water is colder, denser, and more-saline. This separation of water layers is called ocean stratification. Over time, deep water gains heat or loses salinity by exchanging with the mixed layer above, becoming less dense and rising toward the surface. 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 fresh rain. Its surface water is not salty enough to sink below several hundred meters, so deep water in the Pacific must come from other areas.
In the North Atlantic, ocean water is saltier than in the Pacific. This is partly because evaporation on the surface leaves salt behind in the remaining water. Also, sea ice near the Arctic expels salt as it freezes during winter. Another reason is that 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, such as the Tibetan Plateau, the Rocky Mountains, and the Andes, block the return of this moisture to the Atlantic.
Because of these processes, Atlantic surface water becomes salty and dense, eventually sinking to form the North Atlantic Deep Water (NADW). NADW mainly forms in the Nordic Seas, where different water masses, such as Denmark Strait Overflow Water (DSOW), Iceland-Scotland Overflow Water (ISOW), and Nordic Seas Overflow Water, mix. Water from the Labrador Sea may also play a role, but recent evidence suggests that water from the Labrador and Irminger Seas mainly circulates within the North Atlantic Gyre and does not strongly connect to the rest of the AMOC.
NADW is not the deepest water layer in the Atlantic Ocean. The densest and deepest layer is Antarctic Bottom Water (AABW), which is found in any ocean basin deeper than 4,000 meters (2.5 miles). As AABW rises, it mixes with and strengthens NADW. The formation of NADW starts the lower part of the circulation. The sinking of water to form NADW is balanced by an equal amount of rising water. In the western Atlantic, wind activity causes strong upwelling in the Canary Current and Benguela Current, which are located along the northwest and southwest coasts of Africa. As of 2014, upwelling near the Canary Current is stronger than near the Benguela Current, though this pattern was different before the Central American Seaway closed during the late Pliocene. In the Eastern Atlantic, upwelling occurs only during certain months because this region depends more on sea surface temperature than wind activity. There is also a long-term upwelling cycle that matches the El Niño/La Niña cycle.
At the same time, NADW moves southward. Around the southern end of the Atlantic Ocean, about 80% of NADW rises in the Southern Ocean, connecting it to the Southern Ocean overturning circulation (SOOC). After rising, the water takes one of two paths. Water near Antarctica is likely cooled by sea ice and sinks again, joining the AABW or continuing to the Pacific and Indian Oceans. Water that rises at lower, ice-free latitudes moves northward due to wind-driven movement and becomes part of the upper circulation. Warm water in the upper circulation 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 back into the NADW.
Role in the climate system
Equatorial areas are the hottest parts of the Earth. Due to heat movement, this heat travels toward the poles. Most of this heat is carried by wind patterns in the atmosphere, but warm ocean currents also help move it. Heat from the equator moves either north or south. In the Atlantic Ocean, heat flows 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 Sea. While the Gulf Stream is mainly driven by wind, its northern part, the North Atlantic Current, gets much of its heat from the AMOC, which is a deep ocean current that moves water based on temperature and salt differences. The AMOC carries about 25% of the total heat toward the northern hemisphere and plays a key role in the climate of northwest Europe.
Atmospheric patterns also help move heat, so the idea that northern Europe would be as cold as northern North America without ocean currents 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. For example, the difference in temperature is about 4°C (7.2°F) to 10°C (18°F) depending on the area. Studies of the Florida Current show that the Gulf Stream was about 10% weaker between 1200 and 1850 due to higher salt levels in the ocean, which likely contributed to a period called the Little Ice Age.
The AMOC helps the Atlantic Ocean absorb more carbon in two ways. First, it brings deep, nutrient-rich water to the surface, which supports the growth of phytoplankton and increases the amount of photosynthesis in the ocean. Second, the deep water that rises to the surface has low carbon levels because it is very old and has not absorbed recent human-made carbon dioxide. This water absorbs more carbon than surface water and keeps it from returning to the atmosphere when it sinks again. While the Southern Ocean is the strongest carbon sink overall, 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 ocean water layers with different temperatures and salt levels. These changes can be small and short-term or large and long-term. Many of these changes happened during the Late Pleistocene, which was the last major ice age before the current warm period called the Holocene. This time also included the Last Glacial Period, known as the "last ice age." During this time, there were 25 sudden temperature changes between the northern and southern hemispheres, called Dansgaard–Oeschger events (D-O events). These events were discovered by scientists studying ice cores from Greenland in the 1980s.
D-O events are best known for rapid warming in Greenland, where temperatures rose by 8°C (15°F) to 15°C (27°F) over a few decades. Similar warming happened across the North Atlantic, but the Southern Ocean cooled at the same time. This pattern fits with the AMOC moving more heat between hemispheres. The warming in the northern hemisphere likely caused ice sheets to melt, and some D-O events ended when large amounts of icebergs broke off from the Laurentide ice sheet. As the icebergs melted, the ocean became less salty, slowing the AMOC and ending the warming.
Scientists do not yet fully understand why the AMOC changed so much during the ice age. Some ideas include changes in salt levels in the North Atlantic or shifts in wind patterns caused by ice sheets. Research from the 2010s suggests the AMOC was most sensitive to changes during times with large ice sheets and low carbon dioxide levels, making the Last Glacial Period a time when these changes were common. Some studies suggest the warming in the southern hemisphere started the pattern, as warmer water moved north through the ocean. However, there is not enough evidence to say whether the AMOC changed first or if something else caused the changes. For example, changes in sea ice might have started the D-O events by affecting ocean temperature and circulation through a process called ice-albedo feedback.
D-O events are numbered in reverse, with the largest numbers for the oldest events. The last major event, called D-O event 1, happened about 14,690 years ago and marked the end of a cold period called the Oldest Dryas and the start of a warmer period called the Bølling–Allerød Interstadial. This period lasted until about 12,890 years ago and was named after two sites in Denmark with plant fossils that only survive in warm climates. The warming in the northern hemisphere was balanced by cooling in the southern hemisphere, with little overall change in global temperature. This fits with changes in the AMOC. The warm period also caused a rise in sea levels due to melting ice sheets, known as Meltwater pulse 1A.
The Bølling and Allerød stages were separated by a short period of cooling in the northern hemisphere and warming in the southern hemisphere, called the Older Dryas. This name comes from a plant called Dryas
Stability and vulnerability
The AMOC did not always exist. For much of Earth's history, ocean currents in the northern hemisphere flowed mainly in the North Pacific. Evidence from Earth's past shows that the shift of these currents from the Pacific to the Atlantic happened 34 million years ago, during a time called the Eocene-Oligocene transition. This change occurred after the Arctic-Atlantic gateway closed, which changed how salt and temperature-driven ocean currents worked. Some scientists think that climate change might one day reverse this shift and restart the Pacific currents if the AMOC stops working. Climate change affects the AMOC by warming surface water due to Earth's energy imbalance and by making surface water less salty because of melting ice, mainly from Greenland, and increased rainfall over the North Atlantic. These changes would increase the difference between surface and deep ocean layers, making the upwelling and downwelling that drive the AMOC harder to maintain.
In the 1960s, Henry Stommel studied the AMOC and created a model called the Stommel Box model. This model introduced the idea of Stommel Bifurcation, which suggests the AMOC could exist in either a strong state, like it has been throughout recorded history, or a much weaker state that might not recover unless warming and freshening decrease. Warming and freshening could directly cause the AMOC to weaken or collapse. If the AMOC weakens, its natural variations might push it past a tipping point. Scientists have long debated whether the AMOC is a bistable system that can be either "on" or "off" and might suddenly collapse.
Some models developed after Stommel’s work suggest the AMOC could exist in one or more stable states between full strength and full collapse. These intermediate states are more common in Earth Models of Intermediate Complexity (EMICs), which focus on parts of the climate system like the AMOC and ignore others. More detailed general circulation models (GCMs), which are considered the best for simulating the entire climate, often show the AMOC has only one stable state and is unlikely to collapse. Researchers have pointed out that GCMs may overestimate the AMOC’s stability because they move large amounts of freshwater to the North Pole, where it does not affect the AMOC, a process that does not happen in nature.
In 2024, three scientists used a model called the Community Earth System Model (CESM) to simulate the AMOC. Their simulation showed a classic AMOC collapse, similar to what happens in simpler models. Unlike other simulations, they gradually increased freshwater input over 1,700 years before the collapse occurred. The model reached freshwater 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. These conditions were not realistic, but the researchers said the results help show how ocean currents might change before a collapse. Other scientists agreed the study would help improve future models once better data is available.
Some studies suggest simpler models overestimate the AMOC’s collapse because they assume a constant flow of freshwater. In one study, using a variable freshwater flow instead of a constant one delayed the AMOC’s collapse by over 1,000 years in a typical model. This simulation matched past events, like the Meltwater pulse 1A around 13,500–14,700 years ago. A 2022 study found that massive freshwater input during the final stage of the last ice age had a limited effect on the AMOC, suggesting models may overestimate how much freshwater affects it. If the AMOC depends more on wind strength, which changes little with warming, it might be more resistant to collapse. Some scientists think the Southern Ocean overturning circulation (SOOC) may be more vulnerable to collapse than the AMOC.
High-quality climate models suggest the AMOC is unlikely to collapse unless warming reaches very high levels (≥4 °C or 7.2 °F) and continues long after 2100. Some past studies support this idea. However, some scientists worry that complex models are too stable and that simpler models predicting an earlier collapse might be more accurate. One simpler model suggested the AMOC could collapse around 2065 (updated from 2057 in 2025), but many scientists doubt this prediction. Research also suggests the SOOC may be more likely to collapse than the AMOC. In October 2024, 44 climate scientists published an open letter, stating recent studies show the risk of AMOC collapse has been underestimated and that it could happen in the next few decades, with severe effects for Nordic countries. They urged Nordic nations to follow the Paris Agreement to prevent this outcome.
Trends
Until 2024, scientists noticed a difference between observations showing a slower ocean current and models showing a steady current. In November 2024, a study published in Nature Geoscience aimed to address this issue. Researchers used advanced models that study the ocean and sea ice. After this study, observations and models matched more closely. The study found the current slowed by 0.46 sverdrups each decade since 1950.
Direct measurements of the Atlantic Meridional Overturning Circulation (AMOC) began in 2004 with the RAPID project, which uses underwater sensors at 26°N in the Atlantic. Observations need long-term data to be useful. Some scientists used smaller-scale data, like submarine research in 2005 that found water movement in the Greenland Sea was less than a quarter of normal levels. In 2000, other scientists studied the North Atlantic Gyre (NAG), which is also called the Northern Subpolar Gyre (SPG). Measurements in 2004 showed a 30% drop in the NAG compared to 1992, but later RAPID data showed this was a statistical error. Observations from 2007 and 2008 showed the NAG recovered. Scientists now know the NAG is mostly separate from the AMOC and could weaken on its own.
By 2014, RAPID data up to 2012 showed a decline in the AMOC 10 times greater than models predicted. Scientists debated whether this was due to climate change or natural variability. Data up to 2017 showed a large drop in 2008–2009 but a weaker current after 2008 compared to 2004–2008.
The AMOC is also measured by tracking heat transport. In 2017 and 2019, data from NASA’s CERES satellites and Argo floats suggested 15–20% less heat transport than RAPID data, but showed a stable flow with limited changes over decades.
Measurements of the Florida Current showed it has remained stable for 40 years after adjusting for Earth’s magnetic field changes.
Climate reconstructions use past data to study the AMOC, though they are less reliable than direct observations. In February 2021, RAPID data combined with older records showed no overall decline in the AMOC over the past 30 years. A 2020 study found no major changes in the AMOC compared to the 1990s, though the North Atlantic changed. A 2022 review noted global warming may weaken the AMOC over time, but changes since 1980 are hard to detect because the current has both weakened and strengthened. The review called for more sensitive and long-term research.
Some reconstructions compared the AMOC’s current state to earlier periods. A 2010 study found the AMOC has weakened since the 1930s, with a major shift in the North Atlantic overturning cell around 1970. A 2015 study linked cold temperature patterns to a 15–20% AMOC weakening over 200 years, with the current slowing most of the 20th century. Between 1975 and 1995, the current was weaker than any time in the past millennium. A 2018 study found a 15% weakening since the mid-20th century. A 2021 study used over a century of ocean data to show changes in eight AMOC indicators, suggesting "almost complete loss of stability." This study excluded data from 1900–1980 to keep records consistent. A 2022 study challenged these findings, saying no major AMOC changes occurred between 1900 and 1980, and a small weakening began in 1980, which is within natural variability.
Sediment analysis showed the AMOC weakened by 20% since the mid-20th century. A 2018 study found the AMOC has been unusually weak in the last 150 years compared to the previous 1,500 years. A 2017 review found strong evidence of past AMOC changes during abrupt climate events like the Younger Dryas. A 2022 study found the Atlantic’s long-term variability has increased, making it less likely to return to normal states. This could signal a slow AMOC weakening not seen in most models.
In February 2021, a study in Nature Geoscience found the AMOC weakened significantly over the past millennium, suggesting human actions caused the change. The study’s co-author said the AMOC has already slowed by 15%, and further weakening could increase storms, heatwaves in Europe, and sea level rises on the U.S. East Coast. A 2022 article in Nature Geoscience disputed these findings, saying the long-term AMOC trend remains uncertain. The 2021 study’s authors defended their results.
Some scientists link recent climate changes to AMOC weakening. For example, a large area near Greenland cooled by 0.39°C (0.70°F) between 1900 and 2020, while other oceans warmed. This cooling is seasonal, peaking in February at 0.9°C (1.6°F), but still warms compared to pre-industrial times. Between 2014 and 2016, this area stayed cool for 19 months, a phenomenon called the "cold blob."
The cold blob occurs because fresh, cool water avoids sinking, which some scientists linked to AMOC weakening. Later research found atmospheric changes, like more low clouds and stronger North Atlantic Oscillation (NAO), also contributed to this pattern.
Projections
Historically, CMIP models, which are the most trusted tools in climate science, show that the Atlantic Meridional Overturning Circulation (AMOC) is very stable. These models suggest that even if the AMOC weakens, it will recover rather than permanently collapse. For example, in a 2014 experiment where carbon dioxide (CO₂) levels were doubled from 1990 values and remained unchanged, the AMOC declined by about 25% but did not collapse. It recovered slightly—by 6%—over the next 1,000 years. In 2020, research estimated that if global warming stabilizes at 1.5 °C (2.7 °F), 2 °C (3.6 °F), or 3 °C (5.4 °F) by 2100, the AMOC would weaken for an additional 5–10 years after warming stops but would not collapse. It would partially recover after about 150 years. Many scientists believe that models avoid predicting collapse due to errors in their design.
Although CMIP models have improved over time, the sixth generation (CMIP6), used as of 2020, 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 from 2015 values by 2100 (from about 400 parts per million to over 850 ppm), they predicted a decline of over 50% by 2100. These models also struggle to simulate the North Atlantic Deep Water (NADW) accurately, which reduces confidence in their projections.
To address these issues, scientists tested bias correction in models. In one experiment, applying bias correction to a model caused the AMOC to collapse after 300 years. In 2016, researchers combined data from eight CMIP5 models with improved Greenland ice melt estimates. They found that under a moderate warming scenario (RCP 4.5), the AMOC would weaken by about 18% by 2090–2100, and under a high-emissions scenario (RCP 8.5), it would weaken by 37%. When these scenarios were extended past 2100, the AMOC stabilized under RCP 4.5 but continued to decline 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 model with advanced ocean physics and found that under RCP 4.5, the AMOC weakened similarly to the 2016 study, but under RCP 8.5, it declined by two-thirds after 2100 without collapsing.
In 2023, a statistical analysis of multiple models suggested that the AMOC is most likely to collapse around 2065, with a 95% chance of collapse between 2037 and 2109. However, this study faced criticism because the models used are considered less reliable and may confuse a slowdown with a complete collapse. The study relied on temperature data from a specific region, which some scientists argue does not represent the entire AMOC. Experts noted that while the research was "worrisome," it could be useful once better data is available.
A 2025 study extended CMIP6 simulations beyond 2100 and tracked the deep northern overturning cell (linked to NADW formation). Under a high-emissions scenario (SSP5-8.5), all nine models showed a sharp decline in the AMOC, with overturning transports dropping from about 14–26 Sv to 1–6 Sv by 2100. This was accompanied by a sudden shift in the depth of maximum overturning. The models also showed that the breakdown of deep mixing in subpolar regions preceded the AMOC’s collapse by about 30 years, consistent with feedback mechanisms like Welander and Stommel effects.
Large review papers and reports evaluate model outputs, observations, and historical data to provide expert judgments. The IPCC Third Assessment Report (2001) projected high confidence that the AMOC would weaken but not stop, with warming effects outweighing cooling. The Fifth Assessment Report (2014) stated that a rapid AMOC transition was "very unlikely." The Sixth Assessment Report (2021) said the AMOC is "very likely" to decline in the 21st century but noted only "medium confidence" that it would avoid collapse before 2100. This reduced confidence was influenced by studies highlighting model biases and simpler models suggesting the AMOC may be more vulnerable to abrupt changes.
The IPCC Sixth Assessment Report summarized that the AMOC is "very likely" to weaken over the 21st century but "not expected" to collapse before 2100. If collapse were to occur, it would likely cause sudden shifts in weather patterns and water cycles, affecting ecosystems and human activities. A 2022 assessment of climate tipping points identified the AMOC collapse as a potential event, likely triggered by 4 °C of global warming but possibly at lower levels. It estimated that once triggered, collapse would occur between 15 and 300 years, most likely around 50 years. The collapse of the Northern Subpolar Gyre, a separate tipping point, was predicted to occur at 1.8 °C of warming, with effects including a 3 °C drop in European temperatures and changes in regional precipitation.
The "State of the Cryosphere" report highlights that the AMOC may be approaching collapse due to ice melt and warming. Impacts could include rapid cooling in Northern Europe, with no realistic way to adapt, and significant changes in global weather patterns.
Effects of AMOC slowdown
As of 2024, scientists do not agree whether the AMOC has been slowing down steadily. However, most believe it will slow if climate change continues. The IPCC says that if the AMOC weakens in the future, it could cause less rain in areas around the middle of the Earth, more intense rain in tropical and European regions, and stronger storms that move along the North Atlantic. In 2020, research showed that a weaker AMOC might slow the loss of Arctic sea ice and create weather patterns similar to those during the Younger Dryas, such as moving the Intertropical Convergence Zone further south. These changes would be much greater under high-emissions scenarios.
A weaker AMOC would likely speed up rising sea levels along the U.S. East Coast. At least one event linked to faster sea level rise was tied to a temporary slowdown in the AMOC. This would happen because warmer coastal waters would expand more, trapping more heat near the coast instead of moving it 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 in the AMOC could cause Europe to cool by about 1 degree Celsius (1.8 degrees Fahrenheit). Other areas would be affected differently. A 2022 study found that Siberian winters were milder 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 world’s 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, leading to more global warming, though this view is less common.
A 2021 study linked other major tipping points, such as the melting of the Greenland and West Antarctic ice sheets and the decline of the Amazon rainforest, to the AMOC. It said changes in the AMOC alone are unlikely to cause tipping in these systems. However, a slower AMOC could connect these elements, lowering the global-warming threshold at which tipping might occur. This connection could lead to a series of tipping events over several centuries.
Effects of an AMOC shutdown
A complete collapse of the AMOC would likely be permanent and could take thousands of years to recover. A shutdown of the AMOC is expected to cause significant cooling in Europe, especially in Britain, Ireland, France, and the Nordic countries. In 2002, research compared an AMOC shutdown to Dansgaard–Oeschger events—sudden temperature changes that happened during the Last Glacial Period. That study suggested Europe could experience local cooling of up to 8 °C (14 °F). A 2022 review of tipping points concluded that an AMOC collapse would lower global temperatures by about 0.5 °C (0.90 °F), while temperatures in Europe could drop by 4 °C (7.2 °F) to 10 °C (18 °F).
A 2020 study examined the effects of an AMOC collapse on farming and food production in Great Britain. It found that, after accounting for warming, temperatures in Britain would drop by an average of 3.4 °C (6.1 °F). Rainfall during the growing season would also decrease by about 123 mm (4.8 in), reducing suitable land for farming from 32% to 7%. This could lower the value of British farming by around £346 million per year—over 10% of its 2020 value.
A 2024 study modeled the effects of an AMOC collapse on a pre-industrial world. It predicted a more severe cooling in Europe, with average sea surface temperatures in northwest Europe falling by 10 °C (18 °F) and average February temperatures on land dropping by 10 °C (18 °F) to 30 °C (54 °F) in northern and western Europe within a century. This change could lead to sea ice extending into the territorial waters of the British Isles and Denmark during winter, while Antarctic sea ice would decrease. These findings do not include the warming effects of climate change, and the study’s methods have been debated.
A 2015 study led by James Hansen found that a shutdown or slowdown of the AMOC could worsen severe weather by increasing baroclinicity and speeding up northeasterly winds by 10–20% in the mid-latitude troposphere. This could lead to stronger winter and near-winter cyclonic "superstorms" with hurricane-force winds and heavy snowfall. This paper has also been debated.
Several studies have looked at how an AMOC collapse might affect the El Niño–Southern Oscillation (ENSO). Results vary, ranging from no overall impact to stronger ENSO activity, shifts toward dominant La Niña conditions, and more frequent extreme rainfall in eastern Australia, along with more intense droughts and wildfire seasons in the southwestern U.S.
A 2021 study used a simplified model to examine the effects of an AMOC collapse on the Amazon rainforest and its potential shift to a savanna state in some climate scenarios. It found that an AMOC collapse could increase rainfall in the southern Amazon due to the movement of the Intertropical Convergence Zone, which might help prevent the rainforest from dying back and stabilize its southern region. A 2024 study suggested the Amazon’s seasonal cycle could reverse, with dry seasons becoming wet and wet seasons becoming dry.
A 2005 paper stated that severe disruption of the AMOC would reduce North Atlantic plankton biomass to less than half its normal level due to increased ocean layer separation and reduced nutrient exchange. A 2015 study simulated global ocean changes under AMOC slowdown and collapse scenarios, finding that these events would greatly decrease dissolved oxygen in the North Atlantic, though dissolved oxygen would slightly increase globally due to larger increases in other oceans.