The Atlantic’s great conveyor belt is faltering. The Atlantic Meridional Overturning Circulation (AMOC) - the current that carries warm surface waters north and cold deep waters south - underpins much of Earth’s climate system. For decades, scientists have warned that global warming could slow or even collapse this circulation. What was once considered a remote possibility now looks worryingly near. A recent study suggests breakdown could happen as early as 2100. The social, environmental, and economic aftershocks would not be gradual inconveniences, but a civilisational shockwave.

The economic arithmetic is staggering. Nobel laureate William Nordhaus estimates AMOC collapse would reduce global GDP by 30% - economic devastation comparable to the Great Depression, but potentially permanent and worldwide. Total damages to 2200 could reach $3.1-8.4 trillion, dwarfing the economies of most nations.

Yet even these figures understate the true cost. Recent climate modelling research shows the consequences on both sides of the Atlantic Ocean would be immense, including infrastructure damage from extreme weather and the need for entirely new agricultural systems. The marine ecosystem collapse would cause a fishing famine, with a breakdown of nutrient flows that sustain cod, haddock and herring, devastating protein supplies for billions. Meanwhile, northern European countries would face dramatically increased heating costs precisely when their agricultural productivity vanishes.

Insurance markets would buckle under claims that dwarf anything in human experience. Many regions would become simply uninsurable, forcing governments to shoulder risks that private markets cannot bear.

When scientists speak of AMOC collapse, they are not indulging in academic hyperbole. The breakdown would fundamentally alter the distribution of heat and precipitation globally. A group of 44 leading climate scientists recently warned that collapse risks have been "greatly underestimated".

An AMOC collapse would deliver a wholesale restructuring of the global food system. 58% of the land currently suitable for wheat and 59% for maize would become unusable. Together with rice, these crops supply more than half of global calories. Their collapse would shred food security.

The United Kingdom, which currently enjoys a climate warmer than Newfoundland in Canada, despite sharing similar latitudes, would face temperature declines of 3-7°C. Agricultural production would plummet by 78%, shrinking arable farming from 32% to just 7% of the country's land. Annual losses to British agriculture alone would reach £346 million - roughly 10% of total farming income.

But Europe's suffering would be merely the opening act. West Africa's monsoon systems, which sustain hundreds of millions, would weaken dramatically. The region faces crop yield reductions of 60-80%, potentially displacing 400-800 million people. India's monsoons, critical for 1.5 billion people, could lose 70% of their current rainfall patterns, threatening the subcontinent's agricultural foundation.

The demographic consequences may prove even more destabilising than the economic ones. The Syrian refugee crisis contributed to political upheaval across Europe, with fewer than one million arrivals. Historical analogues and modelling suggest that upwards of 100 million people could become migrants or internally displaced, concentrated in Sub-Saharan Africa, South Asia and, somewhat ironically, Europe. The demographic reshuffling would dwarf any event in recorded history. Political systems would not bend; many would break.

The social fabric would strain under such pressures. History suggests that when agricultural systems fail and populations move en masse, political institutions follow suit. Crop losses drive migration; migration strains politics; politics undermines co-operation. State failure could ensue in vulnerable regions, particularly across the Sahel and parts of South Asia, as governments lose the capacity to feed their people or maintain order.

International co-operation - already fragile - could fracture as nations prioritise domestic crisis response over global co-ordination. Resource wars over the remaining arable land and freshwater become grimly plausible scenarios. Nuclear security risks multiply as affected nations face existential pressures.

The feedback loops are particularly troubling. AMOC collapse would bring abrupt cooling across large parts of the northern hemisphere, changes in tropical rainfall, and non-linear changes in sea-level rise, according to recent scientific assessments. These impacts could undermine society's capacity to respond to climate change, potentially triggering what researchers call "spiralling derailment risk" toward a ‘Hothouse Earth’ state.

The window for preventing this catastrophe is rapidly closing. Current emission trajectories put the world on track for warming well beyond 2°C, the threshold above which AMOC collapse becomes increasingly likely. Limiting warming to below 2°C could minimise collapse risks, but this requires immediate, unprecedented global action.

The AMOC has collapsed before, triggering ice ages and abrupt climate shifts. Humanity has never lived through such an event with billions of mouths to feed and borders to defend. The research suggests collapse could happen within a generation. The consequences would be irreversible on human timescales.

Civilisations fall not just because of the shocks they endure but because they fail to prepare. The AMOC is nature’s reminder that the climate system does not bend gently; it breaks abruptly. The question for policymakers is whether they are prepared for a world where the Atlantic’s great conveyor stops - and whether humanity can prevent it from happening at all.

Expert philanthropically funded groups like the Strategic Climate Risks Initiative are emerging to explore and mitigate emerging climate risks, including AMOC collapse.

The UK's ARIA has awarded £11 million to the UK’s National Oceanography Centre to develop early-warning systems for a potential AMOC breakdown.

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