The Atlantic Meridional Overturning Circulation (AMOC), an essential component of global ocean circulation that includes the well-known Gulf Stream, is facing a potentially catastrophic future under scenarios of continued high greenhouse gas emissions. A groundbreaking study, utilizing advanced climate models and conducted with significant contributions from the Potsdam Institute for Climate Impact Research (PIK), reveals that the AMOC could undergo a complete shutdown sometime after the year 2100. This eventual collapse, far from a distant scientific curiosity, would have profound and far-reaching impacts on weather patterns and climate, particularly in northwestern Europe and tropical regions worldwide.
The importance of the AMOC to the Earth’s climate system cannot be overstated. It functions as a vast conveyor belt, transporting warm, saline tropical waters northward near the ocean’s surface while returning colder, denser waters southward at depth. This circulation helps to moderate the climate of Europe, ensuring relatively mild winters, and influences weather systems on a global scale by regulating temperatures and precipitation patterns. The new research, published in the journal Environmental Research Letters, draws on the Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations, extending projections well beyond the typical 2100 horizon used in most Intergovernmental Panel on Climate Change (IPCC) assessments.
One of the defining features of the study is its revelation that the tipping point sparking the shutdown of the AMOC emerges well before the actual collapse of the circulation system—specifically through a breakdown of deep ocean convection in the winter months within critical North Atlantic regions such as the Labrador, Irminger, and Nordic Seas. This deep convection process normally drives the sinking of cold, dense water, which is vital for maintaining the deep branch of the circulation. However, global warming is significantly reducing ocean-atmosphere heat exchange during winter, due to higher atmospheric temperatures that inhibit heat loss from surface waters. This causes the surface layer to remain warmer and less dense, disrupting the essential sinking mechanism.
As the sinking of cold water diminishes, the vertical mixing of ocean layers weakens, causing surface waters to stay lighter and less saline. This salinity reduction further decreases water density, establishing a positive feedback loop that perpetuates the weakening of the overturning circulation system. Importantly, this feedback loop is self-reinforcing: atmospheric warming initiates the sequence, but the circulation system’s own response perpetuates it. According to the study’s models, this cascade of changes could reach a critical irreversible state within decades, making the eventual collapse of the AMOC inevitable once triggered.
The implications of a shutdown are dire. The northward transport of heat by the AMOC would be drastically reduced, with some simulations predicting heat flows to plummet to less than 20 percent of current levels, or nearly zero in extreme cases. This would translate into profound climatic shifts. Northwestern Europe, currently cushioned from the harshness of high latitudes by the AMOC’s warming influence, would face much drier summers and significantly more severe winter extremes. Changes would also ripple outwards across the tropics, inducing shifts in the location and intensity of tropical rainfall belts, altering the dynamics of monsoons, and potentially promoting droughts or flooding in vulnerable regions.
What is particularly alarming is that these results are consistent across all nine high-emission scenario simulations examined. Even more concerning is that some of the intermediate and low-emission scenario models also indicate the possibility of AMOC shutdown, albeit less conclusively. The critical tipping point—the collapse of deep convection—is projected to occur as early as mid-century, according to the multi-model ensemble results, challenging the previous assumption that the AMOC’s demise is a distant prospect. Early observational data seems to support these projections, as measured convective activity in these North Atlantic deep-water formation regions has already shown decreased intensity over the past decade.
Lead author Sybren Drijfhout from the Royal Netherlands Meteorological Institute highlighted that although some recent variability might influence these observations, their consistency with the modeled trends is striking and warrants urgent attention. The study emphasizes that the time lag between the tipping point and full shutdown could range from 50 to 100 years, but this period offers limited opportunity to mitigate the progressive destabilization once underway.
The models used for this research were critically comprehensive but do have limitations. Notably, they do not fully incorporate the additional freshwater influx resulting from accelerated ice melt in Greenland. This fresh water input could exacerbate the weakening of the AMOC by further reducing surface water salinity and density, suggesting that the real-world risk might be even greater than current models predict. This underscores the importance of immediate and aggressive emission reduction efforts to slow or prevent the approach to this tipping point.
Stefan Rahmstorf, head of the Earth System Analysis department at PIK and co-author of the study, stresses that while it may no longer be feasible to completely eliminate the risk of AMOC shutdown, rapid reduction in greenhouse gas emissions remains the most effective strategy to reduce the probability and severity of this scenario. The potential socioeconomic impacts, including sharply altered weather patterns influencing agriculture, water resources, and ecosystems, amplify the urgency of addressing climate change through effective policy and technological measures.
The conclusion of this research resonates deeply within the climate science community. It forces a reconsideration of the timelines and risks associated with major climate tipping points, particularly those connected to ocean circulation systems. While the AMOC has persisted through natural climatic shifts in the past, current anthropogenic influences introduce unprecedented rates of warming and freshwater input into sensitive regions, pushing the system toward thresholds that may arguably have no parallel in the recent geological past.
The projected collapse of the AMOC is not just an oceanographic phenomenon; it represents a fundamental change in the planet’s climatic engine with potentially irreversible consequences. The intricate interplay between atmospheric warming, oceanic convection, and salinity-driven density contrasts that maintains this circulation is unraveling. Understanding these dynamics through improved simulations and ongoing observations will be critical for refining projections and formulating adaptive strategies.
In summation, the study paints a stark and urgent picture: the once-stable conveyor belt of the North Atlantic is unravelling as climate change accelerates. If emissions continue unabated, the century following 2100 may witness an unprecedented shutdown of the AMOC, reshaping climate patterns with global repercussions. The imperative to curb emissions is clear—not only to protect the stability of this critical ocean circulation system but to safeguard the environmental and societal systems that depend upon it.
Subject of Research: Ocean circulation, specifically the Atlantic Meridional Overturning Circulation (AMOC) and its future under climate change scenarios.
Article Title: Shutdown of northern Atlantic overturning after 2100 following deep mixing collapse in CMIP6 projections.
News Publication Date: 28-Aug-2025
Web References:
DOI Link
References:
Sybren Drijfhout, Joran R. Angevaare, Jennifer Mecking, René M. van Westen, Stefan Rahmstorf (2025): Shutdown of northern Atlantic overturning after 2100 following deep mixing collapse in CMIP6 projections. Environmental Research Letters. DOI: 10.1088/1748-9326/adfa3b
Keywords: Ocean circulation, AMOC, climate change, ocean convection, North Atlantic, Gulf Stream, CMIP6, computational simulation, oceanography, climate tipping points
