Should EAs pay more attention to Climate Tipping Points? AMOC Collapse as a Case Study

By Rebecca Frank @ 2025-06-27T21:48 (+22)

Climate change doesn't rank as a top EA cause area because it already receives substantial funding, is less neglected than other risks, and—under gradual-warming scenarios—seems unlikely to cause human extinction. I broadly agree with that assessment. 

Yet some problems under the climate umbrella do fit EA criteria of scale, neglectedness, and tractability. Climate tipping points in particular could trigger catastrophic feedback loops—mass human suffering, great-power conflict, biodiversity collapse, and wild-animal suffering—while still attracting little targeted funding.

Conversations with long-time climate experts reinforce that most money still flows to mitigation; far less supports adaptation or contingency planning. From a “maximizing impact at the margins” perspective, work that limits damage once a tipping point is crossed looks unusually cost-effective, even if it is unfashionable in some environmental circles (it can feel like “admitting defeat”). Preparedness and response planning could therefore make a decisive difference. I would welcome the community’s perspective on this.

Personally, I appreciate the gravity of AI risk—my husband has worked in AI safety for years—and I also care about Gradual Disempowerment and other global threats. Still, many catastrophes (AI, engineered pandemics, nuclear war, etc.) could result in a common need for civilizational and food resilience. That lens led me to work with ALLFED and study the agricultural impacts of an Atlantic Meridional Overturning Circulation (AMOC) collapse.

After several months of research, preliminary results suggest an abrupt AMOC shutdown could reduce global crop yields by ~11% and put an additional ~300 million people at risk of starvation—about 45× the COVID-19 death toll for perspective.

I’ve compiled these findings in my working paper, “Assessing the Risk of Global Catastrophic Food Failure from AMOC Collapse.” It synthesizes current AMOC science, models potential food-system impacts, and proposes resilience research directions. Feedback and collaboration are warmly invited.

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Assessing the Risk of Global Catastrophic Food Failure from AMOC Collapse

Abstract

This Working Paper assesses whether a collapse of the Atlantic Meridional Overturning Circulation would meet the six Global Catastrophic Food Failure criteria. Integrating key studies and preliminary agricultural impact modeling, we show that AMOC collapse would be long-lasting, severe, globally interconnected, and pose extreme humanitarian risks. We project an ~11 % drop in global crop yields, driving food prices up 30 – 100 % and adding 100 – 500 million undernourished people. Early warning systems, coordinated international action, and strategic use of supply-elasticity levers could reduce impacts. Our results highlight the urgent need for detailed crop-modeling and robust adaptation frameworks to address this threat.

Disclosures & Acknowledgements

This Working Paper presents my independent analysis and conclusions. While I collaborated with Alliance to Feed the Earth in Disasters (ALLFED)—particularly Mike Hinge, who provided assistance with preliminary food‐price modeling and engaged in insightful discussions—all opinions, interpretations, and any errors are my own and should not be attributed to ALLFED or its members. I gratefully acknowledge Mike’s contributions; any remaining shortcomings are my sole responsibility.

Introduction

This analysis applies the criteria established by Wescombe et al. (2025) in "It's Time to Consider Global Catastrophic Food Failures," to assess whether the potential collapse of the Atlantic Meridional Overturning Circulation (AMOC) qualifies as such an event. Below is a table summarizing the findings. 

Overview of the Atlantic Meridional Overturning Circulation (AMOC)

The Atlantic Meridional Overturning Circulation (AMOC) is a critical and extensive system of ocean currents that plays a fundamental role in regulating Earth's climate. It functions by transporting warm, salty water northward from tropical regions within the Atlantic Ocean, while simultaneously moving colder, deep water southward. IPCC AR6 Ch 9 The mechanism underpinning this circulation involves convection in the North Atlantic, where water cools, becomes denser, and sinks several kilometers below the surface before returning southward. Complementing this northern sinking process, southern water gradually rises to the surface driven by wind and oceanic mixing. As it resurfaces in the tropics, this water becomes warmer and saltier due to higher evaporation rates and warmer temperatures. These dual processes—northern sinking and southern upwelling—are the two primary "engines" driving the AMOC. Met Office, AMOC Factsheet (2025)

Beyond heat transport, the AMOC influences the ocean's carbon uptake capacity. Schaumann and Alastrué de Asenjo (2025) note that a weakened AMOC can reduce the ocean's ability to absorb carbon dioxide, thereby exacerbating global warming. Additionally, AMOC collapse would impact sea-level rise, influencing coastal areas across multiple continents. As a central element of Earth's climate system, AMOC profoundly affects weather patterns across Europe, North America, Africa, and Asia. Prominent components of this ocean current system include well-known currents such as the Gulf Stream and the Subpolar Gyre (SPG), both integral to regional climate stability.

Figure 1. Schematic of the AMOC: Red shows near-surface transport and blue shows return flow at depth. Adapted from Met Office Atlantic Meridional Overturning Circulation schematic Factsheet (2025).

AMOC Weakening and Tipping Potential

Historical Cycles

Historical paleo-oceanographic data indicate that AMOC naturally cycles through stronger and weaker phases. During stronger periods, the northward-transported water is warmer and less dense, reducing the sinking process and weakening the circulation over time. Conversely, during weaker phases the northern Atlantic water grows colder and denser, reinforcing and strengthening the circulation.

Anthropogenic Weakening

Whether AMOC is transitioning to a permanently weaker state, potentially tipping over into a collapsed state, is of ongoing scientific debate and limited by model uncertainties. Caesar et al. (2018) found a 15% decline in strength since the 1950s. Their follow-up research (2021) found after a long stable period there were two pronounced weakening periods: one in the mid-19th century and another more severe weakening in the mid-20th century. It is now in its weakest state in the last millennium. Lee et al. (2024) further model AMOC dynamics by combining the anthropogenic effects with its natural variations. They note that anthropogenic factors significantly weakened the AMOC in the 2000s, yet recent natural strengthening have partially offset this trend. They describe the system as currently in a "tug-of-war" condition. This indicates that unless there is significant reduction in GHG emissions, anthropogenic forces may overtake the natural AMOC cycles and cause further weakening in the future.

AMOC collapse probabilities vary considerably in the literature. Smolders et al. (2024) present the highest estimate at 59% chance by mid-century (though this is not a peer-reviewed paper yet). Ditlevsen & Ditlevsen (2023) predict a likely collapse by 2057, with a broad 95% confidence interval ranging from 2025 to 2095. Though, on the lower end, the IPCC AR6 report considers it "very unlikely" (0-10%) to collapse within the 21st century.

Furthermore, Baker et al. (2025) introduce an important caveat by highlighting that the Southern Ocean’s wind-driven upwelling strengthens under high greenhouse gas scenarios, potentially sustaining AMOC at a weaker but stable state, despite substantial warming and freshwater inputs in the North Atlantic. However, this model operates at greenhouse gas concentrations approximately four times pre-industrial levels, about 2.7 times current atmospheric CO₂ concentrations.

Model Uncertainty

Model uncertainties persist largely due to limited observational data, available only since 2004, and significant discrepancies among CMIP5, CMIP6, and paleo-reconstruction models. Additionally, the Subpolar Gyre was thought to be a reliable source of proxy-data, however recent findings suggest SPG may move independently from AMOC variance, adding further complexity to predictive modeling.

AMOC's Role in Tipping Cascades

The AMOC is intricately linked to other critical tipping elements, particularly the Greenland Ice Sheet (GIS). Kriegler et al. (2009) indicate a 25% probability of the GIS tipping within this century, potentially exacerbating AMOC weakening through increased freshwater input into the North Atlantic. AMOC acts as a mediator in tipping cascades since it connects the two hemispheres, therefore if it tips it could have a domino effect on other regional and global tipping points. Wunderling et al. (2021) show that AMOC's collapse could significantly alter regional climate systems, notably weakening the African monsoon, potentially triggering Amazon rainforest dieback which would elevate atmospheric CO₂ concentrations, leading to additional global warming. However, Nian et al. (2023) suggest increased rainfall and lower temperatures in the Southern Hemisphere from an AMOC collapse might actually stabilize the Amazon rainforest, potentially interrupting this critical tipping cascade.

Figure 2. Tipping Point Cascade schematic. Adapted from Lenton et al. (2019)

In summary, the IPCC AR6 underscores that AMOC is very likely to weaken over the 21st century, albeit with low confidence in exact timing. Enhanced freshwater influx from Greenland meltwater is likely to further accelerate this weakening process.

Figure 3. Time series of AMOC from CMIP5 and CMIP6 experiments. Adapted from IPCC AR6 Chapter 9: Ocean, Cryosphere and Sea Level Change

Impacts

Changes in Climate

Modeling studies consistently project that a large-scale slowdown or collapse of the AMOC would trigger pronounced shifts in global and regional climate. On average, global mean temperatures would drop by approximately 0.5 °C, but this modest global cooling masks stark hemispheric contrasts. In the Northern Hemisphere, particularly over Europe, winters would become markedly colder—by a few degrees Celsius in Western Europe and up to 10 °C in northern latitudes—accompanied by more frequent and intense winter storms and prolonged summer droughts Armstrong McKay et al. (2022), Jackson et al. (2015).

Figure 3. Atlantic Meridional Overturning Circulation surface air temperature and precipitation anomaly schematic. Adapted from Jackson et al. (2015).

Simultaneously, the Intertropical Convergence Zone (ITCZ)—the equatorial band of rising air and heavy rainfall—would shift southward, depriving equatorial regions of moisture and exacerbating aridity Van Westen et al. (2024). 

Major monsoon systems would be reorganized. In Africa and Asia, wet seasons would shorten while dry seasons lengthen; in contrast, parts of South America would face shorter dry spells but heavier overall rainfall Ben-Yami et al. (2024):

• West African Monsoon: Annual rainfall reduced by 29.1%
• Indian Summer Monsoon: Annual rainfall reduced by 18.8%
• East Asian Summer Monsoon: Annual rainfall reduced by 3.8%
• South American Monsoon: An increase in annual rainfall of 43.8%
• Southeast Asian Monsoon might see daily precipitation drop by 0.1–2 mm—translating to nearly a rainfall reduction of 30% 

Earlier hypotheses by Drijfhout (2015) that AMOC-driven cooling could temporarily reverse global warming have been overturned by newer work by Schaumann and Alastrué de Asenjo (2025) showing a roughly linear coupling between AMOC strength and oceanic carbon uptake. As AMOC weakens, carbon sequestration declines, allowing atmospheric CO₂ to accumulate and amplify warming elsewhere.

Sea levels would also respond swiftly after the AMOC collapse. Coasts of North America and the U.K. could see rises around 0.5 m, with Northern Europe and Russia experiencing up to 0.8 m Kuhlbrodt, et al. (2009). This would threaten coastal agriculture, disrupt ports—raising freight costs and slowing trade—and inundate fertile delta regions.

Figure 4. Sea level rise from Thermohaline Circulation (THC) breakdown (m) by 2150. The effect of global warming was subtracted. Adapted from Kuhlbrodt et al. (2009)

Crop Yield Decline

Collectively, these climatic changes drive agricultural shocks. On a global scale, average crop yields are estimated to fall by roughly 11%. This is an initial estimate derived from conducting a weighted average of regional crop production (FAO Stat) and various estimates of regional yield loss from the scientific literature. Regional extremes include up to a 30% yield loss in European breadbaskets, a 10% decline in Indian rice production, and near-total collapse of cultivation potential in the Sahel Environmental tipping points and food system dynamics: Main Report (2017). The Global Food Security programme, UK. Where yield loss estimates were not available, the estimated net plant productivity decline of 5% by Vellinga & Wood (2002) was used instead. More rigorous analysis and detailed crop modeling under AMOC collapse conditions is needed. 

Food Price Increase

Estimating the long-run food price response to an AMOC collapse is necessarily speculative, given wide uncertainty around global agricultural adaptation and policy reactions.

Under plausible high- and low-bound assumptions, our baseline scenario suggests a sustained food price shock of roughly 30% to 100%. Such increases would translate into an additional 100–500 million people unable to afford even a minimally caloric diet—a 100%–500% rise over current levels—and a further 340–840 million who could no longer purchase a fully nutritionally complete diet (a 20%–45% increase).

These figures underscore the critical importance of robust early-warning systems, rapid yield-enhancing interventions, and nimble policy measures—particularly around biofuel mandates and targeted social safety nets—to dampen price spikes and protect the most vulnerable populations.

Derailment Risk

Finally, socioeconomic “derailment” risks loom large. As Laurie Laybourn et al. (2023) emphasizes, climate-driven food insecurity would likely trigger migration, social unrest, and nationalist backlashes, siphoning political will and resources away from climate mitigation and adaptation—thereby compounding chaotic feedback loops.

Timelines and Early Warnings

Timeline of Unfolding Impacts

Full AMOC collapse is projected to unfold over approximately 15 to 50+ years, as detailed by Armstrong McKay et al. (2022) with slower biophysical processes—such as new sea-ice formation extending the tail of the collapse timeline.

Pinpointing exact timings for specific impacts remains challenging. However, certain effects—such as a southward shift of the Intertropical Convergence Zone (ITCZ), disruptions to monsoon systems, and pronounced cooling and drying across the Northern Hemisphere—are expected to commence immediately upon collapse and intensify throughout the first decade.

Jackson et al. (2015) provide one of the clearest temporal examples: their modeling indicates that Northern Hemisphere surface air temperatures plunge sharply following collapse, reaching a nadir around years 10–15. 

Figure 5. Anomalies of area-averaged surface air temperatures for the entire Northern Hemisphere (blue) and the Atlantic basin (60°–0°W, 20°–60°N; red). Adapted from Jackson et al. (2015).

This rapid initial cooling, combined with compounding climatic stresses, suggests that global food production could experience abrupt shocks in the early post-collapse period. As Lenton et al. (2023) note:

“Ocean current tipping elements such as AMOC and the North Atlantic Subpolar Gyre could have immediate impacts on food production.”

Early Warning Indicators 

Detecting an impending AMOC collapse relies on monitoring key system metrics:

1. Net Freshwater Transport at 30°S. When the AMOC pumps less warm, salty surface water northward, it also carries less compensating freshwater (return flow) southward. A declining minimum freshwater transport at the southern boundary of the Atlantic indicates weakened overturning cell strength Van Westen et al. (2024).
2. Increasing Autocorrelation. Scientists measure multiple AMOC “fingerprints” including sea-surface temperature and salinity. Recent AMOC observations show that each month’s values are becoming more similar to the previous month’s—indicating slower recovery from perturbations, reflecting reduced system resilience Boers (2021).
3. Rising Variance. Over the past century, the natural ups and downs in AMOC strength have grown larger, meaning the circulation is experiencing bigger swings—another sign it is destabilizing. Boers (2021).

These early warnings, however, must be interpreted cautiously. Direct measurements of AMOC have existed only since 2004, and historical reconstructions are confounded by other climatic variables. Thus, while freshwater transport, autocorrelation, and variance trends can signal destabilization, uncertainties persist Met Office, AMOC Factsheet (2025).

Recommendations for Resilience and Further Research

Crop Yield Impact Research

Conduct high-resolution crop modeling across key producing regions to underpin effective preparedness and response planning. Without a granular understanding of regional yield impacts and total crop losses, adaptation strategies cannot be properly designed. In particular, focused studies on the United States and China—two of the world’s largest calorie producers—are essential to assess collapse impacts and develop targeted solutions.

Northern Hemisphere Adaptation

Shifting agricultural production toward cool-tolerant and drought-tolerant crop varieties could mitigate yield losses under colder, more variable climates.

• Expand on ALLFED’s outdoor growing research in Abrupt Sunlight Reduction Scenarios (ASRS) to address global tipping point scenarios.
• Build upon ALLFED’s existing greenhouse and research to explore resilient solutions post-collapse.

Southern Hemisphere Opportunities

Regions such as Brazil may benefit from increased rainfall and warmer temperatures, potentially expanding crop suitability and yield potential. However, these opportunities must be weighed against the risks of deforestation, biodiversity loss, and the cascading climate impacts of further Amazon degradation.

Sea Level Rise Impact Research

Sea-level rise from an AMOC collapse could damage coastal infrastructure and disrupt ports, increasing freight costs and slowing trade flows. Quantifying these economic impacts is crucial—continual trade will help buffer food shortages—so demonstrating potential losses can strengthen the case for government preparedness measures.

References 

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