Water is pretty cool, right? Drink it, and you’re not thirsty any more; pour it on yourself, and you’re cleaner than ever before; dive in it, and you’re refreshed to the core. But most importantly, water powers one of Earth’s most crucial climate systems: the Atlantic Meridional Overturning Circulation (AMOC).
Now compromised, the AMOC has been pushed into an existential crisis due to human-induced climate change. Its slowdown and potential collapse could have catastrophic impacts on Europe’s weather, global rainfall patterns, and food production around the world. Before all, let’s first clarify what the AMOC is and why it is so crucial.
Representation of the AMOC; Tasoff, 2024, Phys.org
The Atlantic Meridional Overturning Circulation (AMOC) is a core component of our planet’s ocean circulation system, acting like a giant heating system. As warm surface water flows from the tropics to the North Atlantic, it releases heat, warming Europe and making it milder than other regions at similar latitudes. This process is driven by thermohaline circulation, which relies on temperature (“thermo”) and salinity (“haline”). As warm surface water flows from the Tropics toward the North Atlantic, it cools and, in northern latitudes, loses some of its water content to ice formation, leaving the remaining water saltier. The combined increase in salinity and drop in temperature makes the water much denser. This very dense water then sinks into the deep ocean, pulling warmer water from the south to take its place. This process sustains the AMOC’s continuous flow, with the cold, dense water eventually flowing back toward the tropics and rising to the surface in a constant cycle. See video
Problem? Human-induced climate change is threatening the functioning of this entire cycle, putting the AMOC at increasing risk.
Most abrupt temperatures and climate changes in Earth’s history have been linked with instabilities in the AMOC. By studying the past, geologists have identified distinct markers they refer to as the “fingerprints” of an AMOC slowdown. For several decades now, scientists have detected those fingerprints: a century-long cooling trend of the Atlantic cold blob region and a warming along the North American coast. This signals an AMOC slowdown since the mid-twentieth century.
This AMOC slowdown is driven by climate change. Rising temperatures lower water salinity in the Arctic due to melting ice and increased precipitation while also warming surface waters. Together, these changes reduce water density, weakening the Atlantic’s sinking mechanism and gradually slowing the AMOC.
The scary part is that this creates a feedback loop—where the initial change reinforces itself. As the AMOC weakens, it brings less salty water from the south to northern latitudes, making the water in the Arctic region even less dense and harder to sink, which further slows down the AMOC.
This process could eventually lead to a tipping point—a threshold beyond which the AMOC’s slowdown becomes self-sustaining and would lead to a complete collapse, even without further human interference.
Imagine you’re balancing on a chair, leaning back on just two legs. You can push back slowly until a certain point: the tipping point, where you fall over no matter what you do. In this case, the AMOC’s tipping point, leading to its collapse, may have been widely underestimated.
Last month, more than 40 renowned scientists issued an open letter to the Nordic Council of Ministers stressing that the risk concerning the potential collapse of the AMOC has been strongly underestimated – even in the latest IPCC report. This strong stance does not come out of the blue. In recent years, many scientific studies have highlighted the underestimated risk of the AMOC potential collapse. Where the IPCC forecasted a tipping point after 2100, new findings suggest that it could come around 2050 with the current scenario of future emissions.
While some papers highlight ongoing uncertainties in prediction models, relying solely on this to argue that we are far from a tipping point is a very risky bet, given the catastrophic consequences an AMOC collapse would have on our civilization.
Now, this is the spooky part.
An AMOC collapse scenario would have several severe consequences. While the following impacts and figures represent a complete AMOC collapse, a continuous slowdown would bring similar effects, though to a lesser extent.
The collapse of the AMOC would bring dramatic changes to Europe’s climate. As the AMOC slows and potentially collapses, the cold blob in the Arctic region will expand, bringing colder and colder air towards Northern Europe. This shift would have a substantial impact on annual temperatures across the region. In northern Europe, annual temperatures could drop by 1.2°C to 2.5°C. Winter temperatures would eventually take the biggest hit, with a decrease of over 10 degrees in the far north and between 5 to 7 degrees in the UK.
Annual mean temperature change in an idealized future CO2 doubling scenario
in which the AMOC has fully collapsed; Liu et al, 2017, Science Advances.
So now you’re thinking, “Oh, never mind, global warming will eventually compensate for it…”. Right? Well, not so fast. Let’s remember that we’re looking at annual temperature averages here. For this part of Europe, the “zero” annual change is misleading. It results from mean winter temperature dropping by about 4 degrees and summer temperatures rising by roughly the same amount. So, while the average temperature might stay steady over the year, the standard deviation – the difference between the coldest and the warmest day of the year – would drastically increase, meaning much bigger swings in temperature between and within seasons.
In short, a stable annual average does not mean stable temperatures but rather more extreme ups and downs from season to season. For instance, the 1.2°C of global warming experienced in Europe does not mean that each day of the year is exactly 1.2°C warmer. Instead, temperatures have surged to record highs of 48.8°C in Sicily in 2021 and dropped to -35.8°C in the province of Leon, Spain, highlighting the increasing intensity of seasonal extremes.
Additionally, the mix of cold air from northern Europe and hot air from the south isn’t a cocktail I’d recommend. This increase in air temperature contrast will increase the likelihood and strength of extreme events. To give you an impression of the gravity of the situation, in an interview for the Guardian, Stefan Rahmstorf – renowned Oceanographer part of the Potsdam Institute – warns about the fact that he “would expect major extreme weather events that we have not seen in the past”.
But if you think that’s a lot, you haven’t seen the rest. An AMOC collapse would cool the Northern Hemisphere more than the Southern Hemisphere, creating a temperature imbalance that pulls the Intertropical Convergence Zone – a rain belt near the equator – southward.
Why does this matter? Imagine a surplus of water in regions not accustomed to heavy rain and drought in areas that depend on it. Tragic right?
A recent study showed that this southward shift could drastically disrupt three major monsoon systems: The West African, Indian, and East Asian monsoons. Each of these monsoons would experience shorter wet seasons with reduced rainfall coupled with extended dry seasons. This disruption would have severe impacts on agriculture and water availability for the nearly 3 billion people affected by these monsoons.
Annual mean precipitation in an idealised future CO2 doubling scenario
in which the AMOC has fully collapsed; Liu et al, 2017, Science Advances.
Europe would face an overall decrease in precipitation across the continent, though, masking significant regional disparities, particularly in summer. In the Mediterranean region, summer rainfall could increase by up to 35%, raising the risk of flooding in areas unaccustomed to sudden surges in rain. Meanwhile, northern Europe would experience drier summers, leading to more frequent droughts, straining water supplies, and intensifying wildfire regimes.
Due to these significant disruptions in Europe’s seasonal temperatures and humidity, a study suggests that an AMOC collapse could severely reduce crop productivity across key agricultural regions in western, northern, and eastern Europe. The letter issued by more than forty scientists warned that it could “threaten the viability of agriculture in northwestern Europe”.
Eventually, the collapse of the AMOC will also strongly contribute to water-level rise along the southeast American coast. Between 2015 and 2020, the AMOC slowdown has already accounted for 30 to 50% of floods in the region. Additionally, the ocean's capacity to store carbon—a crucial role, as the ocean has absorbed 25% of our emissions since the Industrial Revolution—will be strongly diminished. In turn, an AMOC collapse would significantly accelerate climate change.
This article, rather than a discussion on how doomed we are, serves as a call for immediate action.
The climate crisis has rarely felt more real than with recent climate-driven disasters, like the flooding in Valencia. These events should be a wake-up call for each of us, motivating change at both individual and collective levels.
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