Running AMOC
Running AMOC
When the AMOC collapses it will lower temperatures by up to 10 or 15 degrees in Europe… The last time AMOC stopped and restarted was during the Ice Ages about 115,000 to 12,000 years ago.
The Impending Collapse of the Gulf Stream and its Consequences
The car thermometer registered -24C. I can't tell you if it was genuinely that cold or just so cold the equipment was malfunctioning. If it was official, it would be in the five coldest temperatures ever recorded in the UK.
I can tell you my anti-freeze-laced window wash had frozen solid, not just in the pipes but in the bottle.
Not that it would have had any impact on the thick hoar of ice inside the car. My face and fingers ached. I changed my mind. Today was not a good day to travel.
It was best not to drive anyway—at those low temperatures, gritting the road is ineffective, and even though I hoped the road would soon be ploughed, it was a half-mile unlit track to reach it, with wind-piled snowdrifts who knew how many feet high. And it was a job to dig the car out and then put the chains on just for the first and last half mile of any trip.
We were snowed in, but we were prepared. The Beast from the East—Anticyclone Hartmut—had arrived.
Moscow Rules
“Winds in the east, There's a mist comin' in. Like somethin' is brewin', And 'bout to begin. Can't put me finger on what lies in store. But I feel, What's to 'appen, All 'appened before.”
“Chim-Chim-Cher-ee”, Bert - Mary Poppins
In the Scottish Borders, we’re at the same latitude as Moscow, but we only flirt with the harsher winters of the Eastern Bloc and our northern Nordic neighbours. We’re kept temperate by the “Atlantic Meridional Overturning Circulation” (AMOC) and Polar Vortex.
The AMOC drives the Gulf Stream, bathing the British Isles in a warm shower, while the Vortex - a whirlpool of air over the north pole - traps the Cold in the Arctic.
In February 2018, the vortex failed, and a deep freeze settled over Northern Europe. That winter, we lost trees that had weathered a century of storms—they had grown strong and steadfast against the western wind, only to be struck down from behind when the tide turned. More firewood, then, to add to the store in the stables, itself buried deep in snow that had blown under the bolted door.
These harsh conditions were temporary—caused by a weakening of the Polar Vortex—and Anticyclone Hartmut met Storm Emma, resulting in widespread death, disruption, and destruction. After Poland, with 27 fatalities, the United Kingdom had 17. Scientists are warning that this may become the new normal if the AMOC fails. It may be already failing, but whether it's 2025 or 2099, they are reluctant to tie down a firm date beyond best guesses and probabilities from incomplete models.
Running AMOC
With daily news of rising sea temperature anomalies and runaway global warming, it seems almost absurd to be concerned about a big freeze - but of course, the better term has always been “Climate Change” and a change to more extreme chaotic weather. It’s perfectly logical for the world as a whole to get larger, while specific areas face deeper unprecedented winters. What was a temporary situation with the weak Polar Vortex could become the new normal in Northern Europe once the AMOC collapses. The AMOC is the linchpin in the oceanic conveyor belt that redistributes heat across the planet.
“A collapse from the currently attained strong to the weak mode would have severe impacts on the global climate system and further multi-stable Earth system components.”
This circulation system moderates weather patterns and stabilises temperatures globally by transferring warm water from the equator towards the poles and returning cooler water to the tropics.
“If it collapses, it could lower temperatures by up to 10 or 15 degrees in Europe… The last time Amoc stopped and restarted was during the Ice Ages about 115,000 to 12,000 years ago.”
BBC News.
Warnings from the Deep
"We're observing changes in salinity and temperature gradients that suggest a weakening trend, which is alarming,"
Professor Johan Nilsson of Stockholm University.
In October 2024, over forty climate scientists wrote an open letter warning the Nordic Council of Ministers about the risks of a major change in the Atlantic Ocean's circulation pattern.
They explained how this "collapse" of the Atlantic Meridional Overturning Circulation (AMOC) will significantly impact the climate of the Nordic countries and the rest of the world. Losing this essential mechanism for heat transport in the North Atlantic means major cooling in the Nordic region while surrounding regions warm. This will lead to unprecedented extreme weather events and threaten the very viability of agriculture in northwestern Europe.
Data indicates the AMOC weakening has been accelerating since the mid-20th century. A 2023 study published in Nature Climate Change notes a 15% decrease in strength since 1950, with projections suggesting a potential collapse by 2100 if current warming trends continue.
Potential Global Impacts
This collapse will drastically alter climates worldwide. Northwestern Europe will face severe Siberian winters as the region loses the warming effects of the Gulf Stream. Africa will see more severe droughts, disrupting agriculture and increasing food insecurity. The oceans will reduce their carbon uptake, significant sea-level rises will flood the American Atlantic coast.
Causes of the Collapse
o understand why the Atlantic Meridional Overturning Circulation (AMOC) is at risk of collapsing, we need to look at the delicate balance of temperature and salinity in the North Atlantic—a balance that drives this powerful ocean current. The AMOC functions as part of a global “conveyor belt” that redistributes heat, moderates temperatures, and stabilises climates around the world. This system is complex. Sensitive. Highly susceptible to disruption by climate change.
The Role of Melting Ice and Freshwater Influx
The sinking of dense, salty water in the North Atlantic drives the AMOC. Warm tropic water flows northward, it cools and evaporates, increasing its salinity and making it denser. This dense water sinks. It creates a downward flow that pulls warm surface water in.
Accelerating glacial melt in Greenland and the Arctic is flooding fresh water into the North Atlantic, diluting the salinity and reducing the water's density. This fresh water weakens the sinking process, which then disrupts the entire AMOC system (Rahmstorf, 2006).
This is one of the most critical factors threatening AMOC stability. According to Bamber et al. (2018), the Greenland Ice Sheet alone is melting at unprecedented rates, contributing vast amounts of freshwater to the North Atlantic. This influx of freshwater interferes with the natural density-driven sinking process, creating a “freshwater cap” that prevents warm tropical waters from moving northward, slowing down the AMOC and potentially leading to a shutdown.
Temperature Changes and Density Gradients
The AMOC relies on temperature gradients between the warm tropics and cooler poles. As global temperatures rise, the gradients are diminishing, altering the density differences that drive the circulation. The IPCC (2021) highlights that higher atmospheric temperatures are warming ocean surface waters, reducing the ability of these waters to cool and sink in the North Atlantic. This warming effect disrupts the natural heat and density distribution that powers the AMOC, adding further instability.
The interplay of temperature and salinity “thermohaline circulation”—is crucial to AMOC’s function. But as ocean temperatures rise and Arctic ice melts, the thermohaline “pump” is weakening, putting the AMOC at risk.
This system is highly chaotic and unpredictable. Chaotic doesn't mean random rather that small changes in temperature or salinity can have outsized effects, creating conditions for abrupt shifts in circulation patterns (Dijkstra & Ghil, 2005).
The Chaotic Nature of Ocean Currents
The AMOC operates within a highly chaotic, non-linear system. Ocean currents are influenced by a complex web of feedback loops—small disruptions in one area can cascade, creating larger, often unpredictable consequences elsewhere. This chaotic nature makes it challenging to model AMOC accurately, with even minor environmental changes potentially triggering a collapse. Studies do suggest that the AMOC has "tipping points" beyond which it may not be recoverable (Boers, 2021).
The Role of Greenhouse Gases in AMOC Weakening
Greenhouse gas emissions are an underlying force driving AMOC destabilisation. Carbon dioxide, methane, and other greenhouse gases trap heat in the atmosphere, warming the oceans and accelerating ice melt. The IPCC’s Sixth Assessment Report (2021) indicates that continued emissions will increase sea surface temperatures and drive further fresh water into the North Atlantic.
This intensifying heat disrupts natural oceanic processes, directly influencing the delicate thermohaline circulation that sustains AMOC.
I can't overstate how far out of the park the current sea level temperatures currently are. Sea temperatures have reached unprecedented levels, with many scientists warning of a potentially catastrophic shift.
In 2023, global ocean surface temperatures shattered previous records, hitting an average of over 21°C, with some regions, like the North Atlantic, warming 5°C above typical seasonal temperatures. 2024 isn't looking much better.
This spike in sea temperature anomalies is a clear indicator of accelerating climate breakdown. Oceans absorb over 90% of excess heat from global warming, but the system appears to be reaching its limits. Such intense and sustained warming destabilises marine ecosystems, disrupts oceanic currents, and accelerates the melting of polar ice, pushing the planet closer to critical climate tipping points.
The current state of ocean warming is “alarming” and “far worse than most models predicted,” with the Atlantic, Pacific, and Indian Oceans all reporting unprecedented heat anomalies (Cheng et al., 2023). These anomalies are not just records—they are warning signals, indicating a trajectory toward runaway climate impacts if urgent action is not taken.
The AMOC’s vulnerability to these combined pressures underscores the urgency of climate action. Exact predictions are difficult to make. Scientists can only outline probable outcomes based on observed trends, stressing that, while we may not be able to pinpoint exactly when AMOC will collapse, the risk is growing as climate change progresses.
But Baby, It’s Cold Outside
In terms of practical preparations for extreme winters -, many good guides are available free online from areas that are more used to them, such as this one from Montana - = https://myfwp.mt.gov/getRepositoryFile?objectID=94015
But the long-term issue is not just weathering a storm, having a snow shovel and chains and several days supply of food in your vehicle. We are talking about a fundamental shift in the nature of how our society can function.
What will the Socio-economic impact be of a 10-15°C Temperature Decrease?
Agricultural Challenges
Crops like maise, wheat, and other cereals that thrive across the UK are at risk. Shorter growing seasons and unexpected frosts spell trouble. We're already reliant on food imports, but if we don't act soon, our existing homegrown food systems will not survive. We could switch to more resilient crops like barley, oats, and root veggies like swedes and carrots. Potentuially explore frost-resistant crops through genetic tweaks or selective breeding, and adjust planting times and tweak farming methods to squeeze out every possible yield in these shorter seasons.
But we probably won't, or won't enough, or not in time.
Our woodlands will also feel the chill. Native trees like the English oak simply may not make it if the mercury drops too low, impacting everything from bugs to birds that depend on these forests.
Infrastructural Challenges
Energy and transport are already under pressure. With colder winters the need for heat will soar, pushing our energy systems to the brink. Blackouts could become a common feature of our winters. Snow and ice could make travel treacherous or even impossible at times. More investment in snow-clearing gear and better rail systems could keep us moving.
Buildings
Most of our buildings aren't cut out for this new icy era. Many are poorly insulated with outdated heating—issues that will only become more apparent as the temperatures continue to fall. Recent decisions, like the ban on wood-fired heaters in Scotland, will leave many unresilient in the Cold during power cuts.
Impact on Our Economy and Civilisation
Health risks will jump. Hypothermia will lead the charge, especially among the elderly and vulnerable. This will put extra pressure on our already stretched-thin healthcare systems. And if every civilisation is only three meals from revolution—well, even the short 2018 freeze saw empty shelves in supermarkets—a colder climate could disrupt everything from farming to supply chains, hitting your pockets hard and possibly leading to a serious economic slump.
The weakening of the AMOC should be a screaming warning to competing nation states that civilisation is not the natural state of the earth and only exists by virtue of the goldilocks zones we have carved out that are not too hot, too cold, too wet, or too dry.
The AMOC is only one of many natural forces that we barely understand, yet by whose good grace our civilisation, as we know it exists.
When AMOC collapses, there's a strong possibility we will collapse, too.
References
Becker, E., & Nilsson, J. (2023). Observational and model evidence for a weakening Atlantic Meridional Overturning Circulation. Nature Climate Change.
Johnson, S. (2023). The socioeconomic impacts of a potential AMOC collapse. University of Leeds.
Cartwright, H. (2023). Ethical dimensions of climate change and global stewardship. Philosophical Transactions of the Royal Society.
Boers, N. (2021). Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation. Nature Climate Change, 11, 680–688. https://doi.org/10.1038/s41558-021-01097-4
BBC. (n.d.). Retrieved from https://www.bbc.co.uk/news/science-environment-66289494
NASA’s Scientific Visualization Studio. (n.d.). Retrieved from https://svs.gsfc.nasa.gov/5176/
Technical University of Munich. (n.d.). Niklas Boers. Retrieved from https://www.professoren.tum.de/en/boers-niklas
Chim Chim Cher-ee Lyrics – Mary Poppins Musical. (n.d.). Retrieved from https://www.allmusicals.com/lyrics/marypoppins/chimchimcheree.htm
Bamber, J. L., Oppenheimer, M., Kopp, R. E., Aspinall, W. P., & Cooke, R. M. (2018). Ice sheet contributions to future sea-level rise from structured expert judgment. Proceedings of the National Academy of Sciences, 116(23), 11195-11200.
Boers, N. (2021). Observation-based early-warning signals for a collapse of the Atlantic Meridional Overturning Circulation. Nature Climate Change, 11(8), 680-688.
Dijkstra, H. A., & Ghil, M. (2005). Low-frequency variability of the large-scale ocean circulation: A dynamical systems approach. Reviews of Geophysics, 43(3).
Intergovernmental Panel on Climate Change (IPCC). (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.
Rahmstorf, S. (1995). Bifurcations of the Atlantic thermohaline circulation in response to changes in the hydrological cycle. Nature, 378(6553), 145-149.
Ice sheet contributions to future sea-level rise from structured expert judgment — TU Delft Research Portal. https://research.tudelft.nl/en/publications/ice-sheet-contributions-to-future-sea-level-rise-from-structured-
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Cheng, L., Abraham, J., Hausfather, Z., & Trenberth, K. E. (2019). How fast are the oceans warming? Science, 363(6423), 128-129.
Cheng, L., Abraham, J., Trenberth, K. E., Fasullo, J., Boyer, T., Locarnini, R., ... & Zhu, J. (2023). Another year of record heat for the oceans. Advances in Atmospheric Sciences, 40(5), 1-5.
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National Oceanic and Atmospheric Administration (NOAA). (2023). Global ocean surface temperatures break records. NOAA Climate.gov.
Rahmstorf, S. (2006). Thermohaline Ocean Circulation. In H. A. Dijkstra (Ed.), Nonlinear Physical Oceanography (pp. 133-158). Springer.
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