Atlantic HVAC Collapse: Part Duex

Source: Guardian.

As reported by Responsible Alpha one year ago, as greenhouse gas emissions warm and freshen the North Atlantic, a new study warns that the AMOC could collapse more likely than we thought, reshaping weather patterns, sea levels, and ecosystems for centuries. While uncertainty remains, the direction of risk is clear. Businesses and investors that understand and prepare for AMOC-related impacts will be better positioned to manage climate volatility, protect assets, and build long-term resilience in a changing world.

Why This Matters

• Businesses: the AMOC influences weather, energy demand, and sea levels, all of which affect operations and supply chains.

• Investors: changes in the AMOC can affect long-term returns by influencing agriculture, real estate, energy, and insurance markets. 

What is the AMOC?

The Atlantic Meridional Overturning Circulation (AMOC) is a vast system of ocean currents that moves warm, salty water northward near the surface and sends colder, denser water southward at depth. This is powered by differences in temperature, saltness, and together, density.

It acts as the Atlantic’s climate engine, keeping Europe and the U.K. far warmer than their latitude would otherwise indicate and shaping rainfall patterns across the Americas and Africa. But with continued carbon emissions, scientists warn that this circulation could change faster and more severely than once thought.

What did the new study find?

A recent study extended climate model projections beyond the usual 2100 cutoff to 2500. It found that under high-emission scenarios, about 70% of model simulations led to a complete AMOC collapse. This is a risk much higher than previously believed.

Even under intermediate and low emissions, the probabilities remained concerning: 37% and 25%, respectively. The findings suggest that what was once considered a “low-likelihood, high-impact” event may now be a plausible long-term outcome under continued carbon emissions.

Why is it changing?

The AMOC’s “engine” relies on cold, salty water in the North Atlantic becoming dense enough to sink. But today, that balance is shifting. Surface waters are warming and freshening, making it less dense, due to Greenland ice melt, sea-ice loss, increased rainfall, and river runoff. These changes weaken the deep-water formation that drives the overturning.

As this process slows, heat transport to the north declines, weakening the entire circulation. The study’s model results indicate that once deep mixing collapses, the AMOC could wind down over decades, with lasting impacts on climate, ecosystems, and sea level.

What happens if the AMOC collapses?

A full or partial collapse of the AMOC would cause profound and likely irreversible disruptions across the planet. In Europe and the U.K., winters could become colder, and summers turn drier, shifting agricultural zones and challenging food production. In the tropics, rainfall belts would likely move southward. The world’s fisheries and ocean ecosystems would be reshaped as nutrient cycles and marine habitats change, threatening aquaculture economies.

Meanwhile, the energy and utilities sectors would face greater volatility, as altered temperature, hydrology, and wind patterns make power generation and demand forecasting less predictable. These are not just environmental shifts, they represent economic and investment risks that could reverberate through supply chains, infrastructure systems, and insurance markets worldwide.

The Scientific Debate

The science doesn’t agree. Some research suggests the AMOC is more resilient, projecting weakening but not total collapse this century. However, the recent study around elevated collapse risk has shifted attentions towards treating serious AMOC weakening or collapse as a credible threat, especially without rapid, deep emissions cuts.