The possible collapse of the Gulf Stream would have drastic effects on the climate, especially in northern Europe, and would have a global impact on various climatic and ecological aspects. This may sound catastrophic, but science has shown that the planet Earth has experienced this dramatic event many times. The AMOC is one of the factors stabilising the climate in Western Europe by transporting heat from the tropics to the North Atlantic. If this current were to stop, Europe would face much colder winters, with a noticeable drop in temperatures, the recovery of glaciers and possible extreme weather events. This could transform Europe’s climate, making it more similar to the cold and severe climate of Canada, which is at a similar latitude.
Oceanography asserts that the disruption of the AMOC would affect other oceanic and climate systems. The loss of this northward flow of heat would alter the pattern of rainfall and NAWLDs in various regions of the planet, leading to major changes in agriculture and freshwater availability in places like Africa and South America. In addition, the AMOC contributes to the circulation of nutrients and oxygen in the North Atlantic, which supports rich marine biodiversity. A collapse would affect not only the species that depend on these nutrients, but also the fishing industries and the economies of communities that depend on the sea. These profound and prolonged changes could alter both ocean ecosystems and global economies, demonstrating that the AMOC plays a critical role in the planet’s climate and ecological stability.
What is the Gulf Stream and the AMOC?
Oceanography – the science that studies the seas, oceans and their related factors – defines the Gulf Streamas a specific surface current that is made up of warm waters flowing from the Gulf of Mexico northeastward along the east coast of the United States and into Europe. It is responsible for moderating the climate of the east coast of North America and Western Europe by bringing warmth from the tropics.
The Gulf Stream is one of the most powerful oceanic forces on the planet. It runs 10,000 kilometres from the warm Gulf of Mexico to the cold coasts of Europe, shaping climates and accelerating crossings. With a width of up to 150 kilometresand depths of up to 800 metres, this monumental current moves at a speed of 6 to 9 kilometres per hour, carrying warm waters of 24°C to 30°C northwards. It is much more than just a current: it is an artery of heat that gives life to Western Europe and, since the time of explorers like Columbus and geniuses like Franklin, has been the natural way to cross the ocean. The Gulf Stream is the true engine of the Atlantic, the conveyor belt of energy that connects continents and sustains ecosystems.
On the other hand, the AMOC, or Atlantic Meridional Overturning Circulation, is a much wider and deeper system of ocean currents . The AMOC includes several currents – such as the Gulf Stream – and relies on the difference in temperature and salinity between water masses known as the thermohaline circulation to transport heat in a complete and deep cycle across the Atlantic.
The AMOC comprises a series of interconnected ocean currents in the North Atlantic that together allow the movement of warm and cold waters in a cycle that regulates climate. In addition to the Gulf Stream, it includes other important currents including the North Atlantic Current. This transports warm waters from the end of the Gulf Stream to the northeast, approaching Europe. Also the Labrador Current, which carries cold waters from the Arctic southward along the east coast of Canada and contributes to cooling the waters in the North Atlantic. And finally, the Greenland and Iceland-Norway currents, which also carry cold water into the North Atlantic and sink due to their high density.
The discovery of the Gulf Stream
The first hint of the existence of the AMOC came to Christopher Columbus during his voyages to America in the late 15th century. During expeditions sponsored by the Spanish Empire, Columbus noticed strong ocean currents that propelled his ships westward from the eastern Atlantic, which facilitated their voyage to the New World.
Later, the Spanish explorer Juan Ponce de León, during his expedition in 1513 where he discovered and christened Florida, encountered the intense currents of the Gulf Stream, which diverted his vessel and made navigation difficult. From the 16th century onwards, the Gulf Stream became a well-known route used by other illustrious Spanish sailors such as Pedro Menéndez de Avilés, Hernando de Soto and Álvar Núñez Cabeza de Vaca. This ‘rolling tapestry’ on the sea helped to significantly reduce navigation time and optimised the routes between Spain and its viceroyalties in America.
Finally, it was Benjamin Franklin in 1769 who made the first formal study of the Gulf Stream. His research succeeded for the first time in detailing on a map the route of this current and instructed sailors to take advantage of it on voyages to Europe and avoid it on their return, optimising time and fuel consumption on transatlantic journeys. This map of the Gulf Stream, a pioneer in oceanography, is now preserved in the Library of the American Philosophical Society in Philadelphia, as well as an original copy in the Bibliothèque Nationale de France in Paris.
Heating Europe: the Gulf Stream and the WCOW
The Gulf Stream and the AMOC act as a temperature moderator in Europe. To understand this, we can imagine the AMOC as a ‘natural lift’ of seawater: warm, salty waters from tropical regions rise northwards at the surface, and when they reach the colder areas near Greenland and the Arctic, they cool, become denser and sink into the deep ocean. From there, they return southwards in a cycle that balances temperatures in different parts of the globe and plays a key role in Europe’s temperate climate.
Thanks to the constant flow of warm water northwards, the AMOC allows Western Europe to have less severe winters and milder temperatures compared to other regions at similar latitudes, such as eastern Canada or Siberia.
As the reader can see, the AMOC is more than just a stream: it is an interconnected and vital system that acts as Europe’s natural “heating system ’ and is crucial to the global climate balance.
Can the Gulf Stream and the AMOC slow down, causing us to enter an ice age?
Of course it can. In fact it has already happened several times. The AMOC, as a natural system, has experienced variations in strength and intensity over the centuries, which has had significant effects on the climate of Europe and the North Atlantic. Historically, there have been periods when the AMOC has slowed down or temporarily stopped, causing episodes of cold weather over the European continent.
In recent climate history, there is evidence of pauses or slowdowns in the AMOC during natural climate change events. For example, during the Little Ice Age (roughly between the 14th and 19th centuries), Europe experienced unusually cold winters, and scientists believe that a weakened AMOC may have contributed to this cooling. Temperatures at this time are documented to have dropped considerably, and the weather became more extreme, with frequent snowfalls and frosts in regions such as Alsace-Lorraine well into the spring. These periods coincide with evidence of pauses or slowdowns in the AMOC and allow us to study how the climate system responded in cooling situations.
But how are the variations in the Gulf Stream known since the 14th century?
Information on the functioning of the Gulf Stream in times before modern instrumentation is provided by climate proxies, or indirect indicators of climate. Among the most important are ice cores in Greenland and Antarctica, which contain trapped air bubbles that reflect past atmospheric composition and temperatures, and tree rings, which show the climate of each year through their thickness: narrow rings indicate cold, dry years, while wide rings reflect warm years. Ocean sediments and corals are also used, which, through their isotopic compositions, indicate changes in water temperatures and salinity, key factors in inferring the strength of the AMOC.
In addition, historical records, such as accounts of extreme winters and crop failures, also help to reconstruct the climate of certain periods in history. Combining these proxies allows scientists to approximate past AMOC activity and understand how it fluctuated in response to natural changes, even without direct measurements.
In the current context, global warming may accelerate a weakening of the AMOC, and while similarities to past cooling cycles are observed, the increase in global temperature introduces new variables. The AMOC could reach a pause similar to these historical periods, but the ongoing warming raises questions about whether the effects would be identical to those in climate history. Such AMOC ‘cycles’, such as those that occurred during the Hundred Years War or in periods of Alpine glacier expansion, could be repeated, but with unpredictable effects due to the intervention of global warming in the process.
The historical periodicity of the AMOC also suggests that there are cycles of weakening and recovery, meaning that the Atlantic circulation system may be more resilient than some climate models suggest. However, if global warming accelerates ice melt in Greenland and other Arctic glaciers, freshwater input to the Atlantic could disrupt or hinder the resilience of the AMOC, leading to a prolonged weakened state or premature pause in its cycle including the collapse of the Gulf Stream.
Analysis of the probability of collapse (2025-2090) according to the University of Utrecht
The study, published in February 2024, from Utrecht University in the Netherlands suggests that the AMOC could collapse anytime between 2025 and 2090 with a probability of 95%. This prediction has raised concerns because of the impact that a collapse of this magnitude could have on the European and global climate. However, while the results are alarming, we believe it is important to consider the basis and limitations of these calculations.
A simulation, not a reality
The Utrecht research relies on advanced mathematical models, which consider thousands of interconnected variables, such as water temperature, salinity and melt rate in the Arctic and Greenland. These models make it possible to simulate the behaviour of the AMOC under conditions of accelerated global warming and predict a possible disruption in the coming decades. Although the study was published in a reputable scientific journal, its predictions should be treated with caution. Climate models, however complex and detailed, are still simplified representations of reality. As expert Andrew Watson, from the Department of Marine and Atmospheric Sciences at the University of Exeter, pointed out, ‘a simulation is not reality’. The behaviour of the AMOC depends on multiple external factors and interactions that may not be fully captured in these models.
The impact of melting ice
A key factor in predicting a collapse of the AMOC is the melting of glaciers and ice sheets in Greenland. As these ice sheets melt, they release large amounts of freshwater into the North Atlantic, lowering the salinity and thus the density of the water.
‘As the Greenland ice melts, large amounts of freshwater are released into the North Atlantic – decreasing salinity and water density – which can reduce the flow of the Gulf Stream’.
In theory, this weakens the ability of the waters to sink and return south, which is vital to the AMOC cycle. However, as Professor Jonathan Bamber of Bristol University has pointed out, the amount of freshwater used in the simulation is much larger than reality, and could influence the accuracy of the predictions.
The prediction that the collapse may occur sometime in the future – between 2025 and 2090 – reflects a significant range of uncertainty. According to experts, this range indicates the difficulty of accurately predicting when (or even if) the AMOC ‘tipping point’ will be reached. Although the study suggests a high probability, some scientists believe that it may take longer before a collapse of such magnitude is plausible.
It is highly unlikely that the Gulf Stream will collapse in the 21st century.
To delve deeper into the methodological limitations and uncertainties of studies on the potential collapse of the AMOC or Gulf Stream, it is worth exploring some details on the use of predictive models and their proxies, the reliance on limited historical data, and the criticisms of experts in oceanography and glaciology. Although the Utrecht University and Copenhagen University studies have been published in reputable journals, such as Science Advances and Nature Communications, and have been endorsed as relevant research, they also face criticismsthat must be considered to give a complete picture of the current state of knowledge on the AMOC.
First, one of the main challenges in modelling a system as complex as the AMOC is the reliance on simulations and computational modelling. Researchers in Utrecht and Copenhagen use advanced mathematical models that integrate thousands of interconnected variables, including water temperature, salinity and the amount of freshwater derived from melting ice in Greenland and the Arctic. These models make it possible to simulate the dynamics of the AMOC under global warming conditions and to predict how it might evolve in the future. However, a simulation is still a simplified representation of reality, and there are external factors and complex interactions in the oceans that current models cannot capture.
In addition, the models used in these studies are based on specific assumptions that, in some cases, have been challenged. Jonathan Bamber, a glaciology expert at the University of Bristol, pointed out that
‘the simulation includes a forced freshwater input equivalent to a six centimetre rise in sea level per year, an amount significantly greater than the historically observed rate of melting.’
This implies that models may overestimate the impact of freshwater on the AMOC, creating an extreme scenario that may not reflect actual conditions. For context, the current rate of melt and the resulting freshwater input to the Atlantic are high, but not yet at the level considered in some models, suggesting that these models may generate more alarming forecasts of collapse than necessary.
Another significant limitation is the paucity of extensive and reliable historical data on the AMOC. Penny Holliday, head of marine physics and ocean circulation at the National Oceanography Centre in the UK, explained that
There is no evidence of a sustained decline in the strength of the AMOC over the past 75 years, which raises doubts about predictions of imminent collapse.
The data currently available are largely from recent observing systems, such as gauging buoys and satellites, which only began collecting detailed information in the last few decades. This means that models must extrapolate trends based on limited data, which can lead to the cyclical nature of the AMOC being overlooked. The thermohaline circulation cycles up and down in intensity, and these variations do not necessarily indicate an irreversible trend towards collapse. The lack of a broader and more consistent time frame makes it difficult to draw definitive comparisons and conclusions.
Finally, some scientists question the data collection methodology in the Utrecht study, which is based on observations made by only five ships in the North Atlantic region. This approach may not adequately capture the variability of an ocean system as large and dynamic as the AMOC. In contrast, more comprehensive studies, such as those conducted by the Intergovernmental Panel on Climate Change (IPCC), incorporate multiple data sources and measurement systems, and while they also consider the possibility of a tipping point in the AMOC, the IPCC assesses that such a collapse is highly unlikely to occur in the 21st century, suggesting that the AMOC, while vulnerable to global warming, may not be on the verge of total disruption in this century.
