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 driven by changes in weather, temperature, and salinity. 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 flow of warm, salty water in the upper layers of the Atlantic and a southward flow of cold, less salty water in the deep ocean. Warm water from the south is saltier because of high evaporation rates in tropical regions. This salty water forms the upper layer of the ocean, but when it cools, its density increases, causing it to sink. This sinking process is a key part of how the AMOC works. The different parts of the AMOC are connected through overturning in the Nordic Seas and the Southern Ocean. These overturning areas help exchange heat, oxygen, carbon, and other nutrients, which are vital for 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 show that by 2015, the AMOC was weaker than it was before the Industrial Revolution. Scientists are still discussing whether this weakening is mainly due to climate change or natural changes over long periods. Climate 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 warmth from the North Atlantic Current. It could also increase sea level rise near North America and reduce the growth of plants and marine life in the North Atlantic.
If the AMOC weakens severely, the circulation might collapse. A collapse would be hard to reverse and is considered a major tipping point in the climate system. This would cause much lower average temperatures and less rain and snow in Europe. It could also increase extreme weather events and have other serious effects.
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, warm, less salty water stays near the ocean's surface, while deeper water is colder, saltier, and denser. This layering of water is called ocean stratification. Over time, deep water gains heat or loses salt through interactions with the mixed layer above, becomes less dense, and rises toward the surface. Differences in temperature and salt levels 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 and partly because sea ice near the Arctic releases salt as it freezes. Additionally, 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 moisture from returning to the Atlantic.
Because of this process, Atlantic surface water becomes salty and dense, eventually sinking to form the North Atlantic Deep Water (NADW). NADW forms mainly in the Nordic Seas and involves interactions between different water masses, such as the Denmark Strait Overflow Water (DSOW), Iceland-Scotland Overflow Water (ISOW), and Nordic Seas Overflow Water. Water from the Labrador and Irminger Seas may also play a role, but recent evidence suggests this water 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 densest and deepest layer is Antarctic Bottom Water (AABW), which exists in basins deeper than 4,000 meters (2.5 miles). As AABW rises, it mixes with and strengthens the NADW. The formation of NADW begins 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-driven ocean currents cause strong rising water in the Canary Current and the Benguela Current, located along the northwest and southwest coasts of Africa. As of 2014, rising water near the Canary Current is stronger than near the Benguela Current, though this pattern was reversed before the Central American Seaway closed during the late Pliocene. In the Eastern Atlantic, rising water occurs only during certain months because this region's deep thermocline makes it more dependent on sea surface temperature than wind activity. A cycle of rising water that lasts many years is linked to El Niño and La Niña events.
At the same time, NADW moves southward. Around the southern end of the Atlantic, about 80% of it rises in the Southern Ocean, connecting with the Southern Ocean overturning circulation (SOOC). After rising, water near Antarctica is likely cooled by sea ice and sinks again, rejoining the AABW or flowing to the Pacific and Indian Oceans. Water that rises at lower, ice-free latitudes moves northward due to wind-driven currents and enters the upper part of the circulation. Warm water in the upper part returns to the North Atlantic mainly along Africa's coast 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 part of the globe. Heat from these areas moves toward the poles because of how heat naturally flows. Most of this heat moves through the atmosphere, but warm ocean currents also help. Heat from the equator moves either north or south. In the Atlantic Ocean, heat flows northward. Much of the heat movement in the Atlantic happens because of the Gulf Stream, a 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, gains heat from the AMOC. The AMOC 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. Some people think northern Europe would be as cold as northern North America without ocean currents, but scientists generally believe this idea is incorrect. One study suggested the AMOC could collapse, causing cooling similar to an ice age, but the accuracy of this is unclear. Scientists agree the AMOC keeps northern and western Europe warmer than it would be otherwise. For example, in some areas, the difference in temperature is about 4°C (7.2°F) or 10°C (18°F). Studies show the Gulf Stream was weaker from about 1200 to 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, deep water rising to the surface brings nutrients that support phytoplankton growth, increasing photosynthesis in the ocean. Second, the deep water that rises has low carbon levels because it is very old and has not been exposed to recent human-made carbon dioxide. This water absorbs more carbon than surface water and stores it 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 depends on interactions between ocean water layers of different temperatures and salinity. It is not static and changes over time. Many changes happened during the Late Pleistocene (126,000 to 11,700 years ago), which was the last ice age before the current warm period. During this time, 25 sudden temperature shifts, called Dansgaard–Oeschger events (D-O events), occurred. These events involved rapid warming in Greenland by 8°C to 15°C (15°F to 27°F) over decades. The North Atlantic also warmed, while the Southern Ocean cooled. This pattern matches the AMOC moving more heat between hemispheres. Some D-O events ended when large icebergs melted, making ocean water fresher and slowing the AMOC.
Scientists are still unsure why the AMOC changed so much during the ice age. Possible reasons include changes in ocean salinity or wind patterns caused by ice sheets. Research suggests the AMOC was most sensitive to changes during the ice age when carbon dioxide levels were low. Some theories say the southern hemisphere warming started the D-O events by moving warm water north. However, evidence is not strong enough to say whether the AMOC caused the events or responded to other changes, such as sea ice affecting ocean currents.
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 start of a warm period called the Bølling–Allerød Interstadial, which lasted until 12,890 years ago. This event was named after two sites in Denmark with fossils from plants that grew in warmer conditions. The warming in the northern hemisphere was balanced by cooling in the southern hemisphere, with little overall change in global temperature. This matches the AMOC’s role in moving heat.
During the Bølling–Allerød period, the northern hemisphere warmed, but the southern hemisphere cooled. This was followed by a short cooling period called the Older Dryas, where Arctic flowers grew in areas that had forests before. The warm period ended with the Younger Dryas (12,800–11,700 years ago), when northern hemisphere temperatures dropped again, possibly within a decade. This happened because the AMOC slowed due to fresh water from melting ice. Unlike earlier events, this was caused by meltwater from the Laurentide ice sheet flowing through the Mackenzie River in Canada. This caused changes in rainfall patterns, with more rain in North America and less in South America and Europe. Global temperatures remained stable during the Younger Dryas, and warming resumed after it ended.
Stability and vulnerability
The AMOC did not always exist; for much of Earth's history, ocean current movement in the northern hemisphere happened in the North Pacific. Paleoclimate evidence shows that the shift of ocean current movement from the Pacific to the Atlantic occurred 34 million years ago at the Eocene-Oligocene transition, when the Arctic-Atlantic gateway had closed. This closure changed the structure of thermohaline circulation. Some researchers suggest that climate change might eventually reverse this shift and re-establish the Pacific current after the AMOC stops. Climate change affects the AMOC by warming surface water due to Earth's energy imbalance and by reducing the saltiness of surface water because of large amounts of fresh water from melting ice, mainly from Greenland, and increased rainfall over the North Atlantic. These changes increase the difference between surface and deep water layers, making the upwelling and downwelling that drive the circulation more difficult.
In the 1960s, Henry Stommel studied the AMOC using a model later called the Stommel Box model. This model introduced the idea of Stommel Bifurcation, which suggests the AMOC could exist in a strong state, like the one observed in recorded history, or collapse to a weaker state and not recover unless warming and/or freshening are reduced. Warming and freshening could directly cause the collapse or weaken the circulation to a state where normal fluctuations might push it past a tipping point. Scientists have discussed 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 have one or more intermediate stable states between full strength and full collapse. These states are more common in Earth Models of Intermediate Complexity (EMICs), which focus on specific 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 a single stable state and is unlikely to collapse. Researchers have noted that GCMs may resist collapse because they redirect large amounts of fresh water to the North Pole, where it no longer affects the circulation, a process that does not happen in nature.
In 2024, three researchers used one of the Community Earth System Models (CIMP) to simulate a classic AMOC collapse, similar to what happens in EMICs. Unlike other simulations, they gradually increased the amount of meltwater input rather than applying unrealistic levels immediately. Their simulation ran for over 1,700 years before the collapse occurred, and they reached meltwater 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) per year rise between 1993 and 2017. The researchers explained that these unrealistic conditions were used to balance the model's stability and that the results should not be seen as predictions but as a detailed view of how currents might change before a collapse. Other scientists agreed that this study would help improve more realistic research once better observational data is available.
Some research suggests that EMIC projections may overestimate the risk of AMOC collapse because they assume a constant flow of fresh water. In one study, the difference between constant and variable fresh water flow delayed the collapse of the circulation in a typical Stommel Bifurcation EMIC by over 1,000 years. This simulation matched reconstructions of the AMOC's response to a major meltwater event 13,500–14,700 years ago. A 2022 study found limited effects from massive fresh water input during the final Holocene deglaciation around 11,700–6,000 years ago, when sea levels rose about 50 m (160 ft). It suggested that many models overestimate the impact of fresh water on the AMOC. If the AMOC relies more on wind strength, which changes little with warming, it may 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 indicate that an AMOC collapse is unlikely unless warming levels (≥4 °C (7.2 °F)) remain high for many years after 2100. Some paleoceanographic research supports this idea. However, some scientists worry that complex models may be too stable and that simpler models predicting an earlier collapse are more accurate. One such model suggests the AMOC could collapse 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 indicate the risk of AMOC collapse has been greatly underestimated and that it could occur in the next few decades, with severe impacts for Nordic countries. They urged Nordic countries to follow the Paris Agreement to prevent this. A 2026 preprint study using high-resolution modeling suggests that an AMOC collapse may be more likely than previous simulations indicated, due to a higher sensitivity to meltwater influx than previously thought.
Trends
Until 2024, scientists noticed a difference between observations showing a slower movement of ocean currents and computer models predicting steady currents. In November 2024, a study published in Nature Geoscience aimed to address this issue. Researchers used advanced computer models that simulate Earth’s systems and ocean-sea ice interactions. After this study, the observations and models matched more closely. The research found that ocean currents have slowed by 0.46 sverdrups each decade since 1950.
Direct measurements of the strength of the Atlantic Meridional Overturning Circulation (AMOC) began in 2004 through the RAPID project, which uses a network of instruments at 26°N in the Atlantic Ocean. Observations require long-term data collection to be useful. Some scientists have used smaller-scale data to make predictions. For example, in May 2005, underwater research led by Peter Wadhams found that water movement in the Greenland Sea—part of the AMOC—was less than a quarter of its usual strength. In 2000, other scientists studied the North Atlantic Gyre (NAG), also called the Northern Subpolar Gyre (SPG). Measurements in 2004 showed a 30% drop in NAG strength compared to 1992, which some thought might signal an AMOC collapse. However, RAPID data later showed this was a statistical anomaly, and the NAG recovered by 2007–2008. It is now understood that the NAG operates separately from the rest of the AMOC and could weaken independently.
By 2014, enough RAPID data had been analyzed up to 2012. These data suggested a decline in ocean circulation 10 times greater than what models predicted. Scientists debated whether this decline was due to climate change or natural variability in ocean currents. Data up to 2017 showed that the decline in 2008–2009 was unusually large, but circulation remained weaker than it was in 2004–2008.
The AMOC is also studied by measuring heat transport, which is linked to ocean current movements. In 2017 and 2019, data from NASA’s CERES satellites and Argo floats suggested that heat transport was 15–20% lower than RAPID measurements indicated, showing a stable flow with limited signs of long-term changes.
Measurements of the Florida Current, a key part of the AMOC, have shown stable strength over the last 40 years after accounting for changes in Earth’s magnetic field.
Climate reconstructions, which use indirect evidence to study past ocean conditions, are less reliable than direct observations. In February 2021, RAPID data was combined with older reconstructions from 25 years before RAPID began. This study found no overall decline in the AMOC over the past 30 years. A 2020 study in Science Advances also found no significant change in AMOC circulation compared to the 1990s, though other parts of the North Atlantic showed changes. A 2022 review concluded that while global warming may weaken the AMOC over time, detecting changes since 1980 is difficult due to both periods of weakening and strengthening. The review called for more precise and long-term research.
Some reconstructions compare the current AMOC to its state a century ago. A 2010 study found the AMOC has weakened since the late 1930s, with a sudden 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, with the strongest slowdown occurring in most of the 20th century. Between 1975 and 1995, the AMOC was weaker than at any time in the past millennium. This study noted a small recovery after 1990 but warned of future declines.
A 2018 reconstruction suggested a 15% weakening of the AMOC since the mid-20th century. A 2021 reconstruction used over 100 years of ocean temperature and salinity data, showing significant changes in eight AMOC indicators that might signal a major loss of stability. This study excluded data from 35 years before 1900 and after 1980 to ensure consistency. However, 2022 research using data from 1900 to 2019 found no AMOC changes between 1900 and 1980, and a minor reduction in strength occurred only after 1980, within natural variability.
Sediment analyses showed a 20% weakening of the AMOC since the middle of the 20th century. A 2018 study found the AMOC has been unusually weak in the last 150 years compared to the previous 1,500 years, suggesting a mismatch in models predicting AMOC 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 showed the Atlantic multidecadal variability has become more persistent, possibly linked to the AMOC, indicating a "quiet" loss of stability not seen in most models.
In February 2021, a major study in Nature Geoscience reported that the AMOC weakened significantly over the past millennium, suggesting human activity caused the change. The study’s co-author stated the AMOC has already slowed by 15% and warned of further weakening in 20–30 years, which could increase storms and heatwaves in Europe and raise sea levels on the U.S. East Coast. In February 2022, a "Matters Arising" article 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 a weakening AMOC. For example, a region of the North Atlantic Gyre near Greenland cooled by 0.39°C (0.70°F) between 1900 and 2020, unlike other areas experiencing warming. This cooling is seasonal, most pronounced in February, but the region still warms compared to pre-industrial levels in summer. Between 2014 and 2016, this area remained cool for 19 months before warming, a phenomenon called the "cold blob."
The cold blob occurs when fresh, cool water avoids sinking into deeper layers. This freshening was initially seen as evidence of AMOC weakening. Later research found atmospheric changes, such as increased low cloud cover and a stronger North Atlantic Oscillation (NAO), also contributed to the cold blob.
Projections
Historically, climate models called CMIP, which are widely used in climate science, show that the Atlantic Meridional Overturning Circulation (AMOC) is very stable. These models suggest that while the AMOC may weaken, it usually recovers rather than collapsing completely. For example, in a 2014 study where carbon dioxide levels were doubled from 1990 levels and stayed the same, the AMOC weakened by about 25% but did not collapse. It only recovered slightly (about 6%) over the next 1,000 years. In 2020, research found that if global warming stabilizes at 1.5°C, 2°C, or 3°C by 2100, the AMOC would weaken for about 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 because they have some errors in their design.
Although climate models have improved over time, the latest generation, called CMIP6 (as of 2020), still has some inaccuracies. On average, these models predict a much greater weakening of the AMOC in response to greenhouse gas warming than earlier models. For example, when four CMIP6 models simulated the AMOC under a scenario where carbon dioxide levels more than double from 2015 values by 2100, they found the AMOC declined by over 50% by 2100. These models still struggle to accurately simulate the North Atlantic Deep Water (NADW), which affects the AMOC, reducing confidence in their predictions.
To improve accuracy, scientists have tested methods to correct errors in models. In one experiment, applying bias correction to a model caused the AMOC to collapse after 300 years in a study where carbon dioxide levels were doubled. In 2016, researchers combined results from eight CMIP5 models with better estimates of Greenland ice melt. They found that under a moderate emissions scenario, the AMOC would weaken by about 18% by 2100, and under a high emissions scenario, it would weaken by about 37%. If these scenarios continued past 2100, the AMOC stabilized under the moderate scenario but continued to weaken under the high scenario, leading to a 74% decline by 2290–2300 and a 44% chance of collapse. In 2020, another study used a model with advanced ocean physics and found similar results for the moderate scenario but showed the AMOC declined by two-thirds under the high scenario, though it did not collapse.
In 2023, a statistical analysis of multiple models suggested the AMOC might collapse around 2065, with a 95% chance of collapse between 2037 and 2109. This study was widely discussed but criticized because the models used are considered less reliable and may confuse a slowdown with a full collapse. The study relied on temperature data from a specific region, which some scientists argue does not represent the entire AMOC. Experts noted the data was not sufficient to support the study’s conclusions.
A 2025 study extended CMIP6 simulations beyond 2100 and tracked the deep northern overturning cell, which is linked to NADW. Under a high-emissions scenario, all nine models showed the AMOC weakened significantly, with overturning strength dropping from about 14–26 Sv to 1–6 Sv by 2100. This was accompanied by a sudden change in the depth of the circulation. The models suggested that the breakdown of deep mixing in the ocean could lead to the AMOC’s collapse, consistent with previous theories.
Large review papers and reports combine model results, direct observations, and historical data to provide expert judgments. The IPCC’s Third Assessment Report (2001) stated with high confidence that the AMOC would weaken but not stop. The Fifth Assessment Report (2014) said a rapid AMOC transition was "very unlikely" with high confidence. The Sixth Assessment Report (2021) said the AMOC is "very likely" to weaken in the 21st century and that changes would be reversible 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 may be more vulnerable.
The IPCC’s Sixth Assessment Report summarized that the AMOC is very likely to weaken in the 21st century but that an abrupt collapse is not expected before 2100. If such a collapse happened, it would likely cause sudden changes in weather patterns and ecosystems. In 2022, a review of climate tipping points identified the AMOC collapse as a possible event, likely triggered by 4°C of warming but possibly at lower levels. If triggered, collapse could occur between 15 and 300 years, most likely around 50 years. A separate tipping point, the collapse of the Northern Subpolar Gyre, was also identified, likely triggered at 1.8°C of warming and occurring within 5–50 years. This collapse could lower global temperatures by 0.5°C and reduce European temperatures by 3°C, with major effects on weather and ecosystems.
A report on the "State of the Cryosphere" noted that the AMOC may be nearing collapse due to ice melt and warming. This could cause rapid cooling in Northern Europe, faster than 3°C per decade, with no clear way to adapt.
Effects of AMOC slowdown
As of 2024, scientists have not reached an agreement on whether the Atlantic Meridional Overturning Circulation (AMOC) has been slowing consistently. However, most experts believe that continued climate change will likely cause the AMOC to slow in the future. According to the Intergovernmental Panel on Climate Change (IPCC), the most likely effects of a future slowdown in AMOC include less rain in mid-latitude regions, changes in rainfall patterns in tropical and European areas, and stronger storms that move along the North Atlantic path. In 2020, research found that a weakened AMOC could slow the loss of Arctic sea ice and lead to atmospheric changes similar to those during the Younger Dryas, such as the Intertropical Convergence Zone shifting southward. These changes would be much more severe under high-emissions scenarios.
A slowdown in AMOC would increase the rate of sea level rise along the U.S. East Coast. At least one event linked to temporary AMOC slowing has already been observed. This would happen because warmer coastal waters would expand, trapping more heat near the coast and reducing heat transfer 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 AMOC could cause Europe to cool by about 1°C (1.8°F). Other regions would be affected differently. A 2022 study found that Siberian winter weather extremes in the 20th century were milder when AMOC was weakened. One analysis suggested that a slowing AMOC might lower the social cost of carbon—a measure of climate change’s economic impacts—by about 1.4%, because Europe contributes more to global GDP than regions harmed by AMOC slowdowns. However, this study may have underestimated 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 less common.
A 2021 study linked other major tipping points, such as the Greenland ice sheet, the West Antarctic Ice Sheet, and the Amazon rainforest, to the AMOC. It stated that changes in AMOC alone are unlikely to trigger tipping points elsewhere, but a slowdown could connect these systems. This connection might lower the global-warming threshold at which these tipping points occur, potentially leading to a chain reaction of tipping events over several centuries.
Effects of an AMOC shutdown
A complete collapse of the AMOC would be difficult to reverse, and it could take thousands of years for the system to recover. If the AMOC shuts down, Europe, especially Britain, Ireland, France, and the Nordic countries, would likely experience significant cooling. A 2002 study compared an AMOC shutdown to Dansgaard–Oeschger events, which were sudden temperature changes during the Last Glacial Period. This study suggested Europe could cool by up to 8 °C (14 °F). A 2022 review of tipping points estimated a global temperature drop of about 0.5 °C (0.90 °F) if the AMOC collapses, while Europe could see temperature drops of 4 °C (7.2 °F) to 10 °C (18 °F).
A 2020 study examined how an AMOC collapse might affect farming in Great Britain. It found that, after accounting for warming effects, temperatures in Great Britain could drop by 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 per year, or over 10% of its 2020 value.
A 2024 study modeled the effects of an AMOC collapse in a pre-industrial world and predicted severe cooling in Europe. It estimated northwest European sea surface temperatures could fall by 10 °C (18 °F), and land temperatures in northern and western Europe could drop by 10 °C (18 °F) to 30 °C (54 °F) within a century. This could bring sea ice into the territorial waters of the British Isles and Denmark during winter, while Antarctic sea ice might decrease. These results do not include warming from climate change, and the study’s methods have been debated.
A 2015 study led by James Hansen suggested that a slowdown or shutdown of the AMOC could increase extreme weather events. This is because it strengthens wind patterns and increases the likelihood of powerful winter storms with strong winds and heavy snowfall. This study has also been debated by scientists.
Research on the AMOC’s collapse and its effects on the El Niño–Southern Oscillation (ENSO) has shown mixed results. Some studies found no major impact, while others suggested stronger ENSO activity or a shift toward more frequent La Niña conditions. This could lead to more extreme rainfall in eastern Australia and more intense droughts and wildfires in the southwestern U.S.
A 2021 study used simple models to examine how an AMOC collapse might affect the Amazon rainforest. It found that the collapse could increase rainfall in the southern Amazon, potentially helping to prevent the rainforest from shrinking into a savanna. A 2024 study suggested the Amazon’s seasonal rainfall patterns could reverse, with dry seasons becoming wetter and wet seasons drier.
A 2005 study noted that severe AMOC disruption 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 would drop significantly in the North Atlantic, though they might slightly increase globally due to changes in other ocean regions.