Antarctic melt may help protect ocean circulation, but not our coastlines

The Atlantic Meridional Overturning Circulation (AMOC) is the ocean’s great conveyor belt, ferrying warm, salty surface waters northward, where those waters cool, sink, and return south at depth.

That overturning hauls an astonishing amount of heat, enough to keep Europe far milder than places at similar latitudes in North America and Asia. But it relies on dense, salty water being able to sink.

Pour in enough fresh, buoyant meltwater from Greenland, and the sinking weakens. This basic physics is why scientists have warned for years that rapid Greenland melt could throttle the AMOC.

Antarctica’s surprising AMOC influence

A new set of simulations led by researchers at Utrecht University explores a twist: meltwater from West Antarctica can, under specific timing, help the AMOC avoid a full collapse.

The team examined different sequences of freshwater entering the Atlantic from Greenland and West Antarctica and tracked how the circulation responded over millennia.

Their headline result is not a reprieve. Even in scenarios where Antarctic freshening “preconditions” the basin, the AMOC still weakens by roughly 60 percent and takes approximately 3,000 years to claw back toward a new steady state.

As researchers noted, people should be cautious about declaring an imminent AMOC crash, but nothing in these simulations softens what the next century looks like.

Experts predict a markedly weaker overturning with very real regional consequences.

Moreover, any stabilizing influence from the south, if it happens at all, plays out on timescales far beyond a human lifetime.

Antarctic melt changes the future

Sequence is everything in this story. When a large pulse of West Antarctic melt enters the system a millennium before Greenland’s peak freshening, the AMOC first sags, then later recovers as the southern pulse wanes.

If, instead, major Antarctic and Greenland melt pulses overlap, the added freshening simply accelerates the near-stall.

The mechanism is intuitive: Greenland runoff caps the subpolar North Atlantic with lighter water, pushing the densest sinking zones southward.

An earlier Antarctic pulse alters basin stratification first, helping the circulation find a different, still viable configuration. Once the Antarctic input ebbs, sinking can strengthen again, but slowly.

Crucially, if all the freshwater arrives together, the system is shunted closer to a tipping threshold. In those runs the AMOC doesn’t neatly “collapse forever,” but it spends a long time in a severely weakened state that would feel like a new normal for multiple generations.

Extreme shifts in a weakened state

A 60 percent slowdown is a profound reorganization of regional climate. Northern Europe would be more vulnerable to deep winter cold snaps.

Storm tracks and rainfall patterns would shift. And sea levels along the U.S. East Coast would ride higher than the global average because a sluggish AMOC piles water up against the shoreline.

In addition, parts of Africa could face more persistent drought. Iceland’s government has even labeled an AMOC shutdown an existential security risk. None of this depends on a total collapse. The weakened state alone is disruptive.

Antarctica’s melt brings huge costs

The supposed “helper” is no gift. The kind of West Antarctic melt large enough to influence the AMOC would raise global seas by up to 9.8 feet (three meters). That would redraw coastlines and swamp defenses for many major cities and low-lying nations.

As Stefan Rahmstorf of the University of Potsdam noted, trading one catastrophe for a slightly reduced risk of another is not a plan.

This study highlights a tighter two-way link between the poles than many had appreciated. According to Louise Sime from the British Antarctic Survey, it adds a new angle to how Southern Ocean changes can modulate the Atlantic.

Yet she also recommends testing the result in more complex Earth-system models. Such models include shifting winds, sea-ice feedbacks, and atmosphere–ocean coupling. All these factors could amplify or blunt the effect.

Collapse risk remains real

Recent assessments have converged on an uncomfortable message: even if global emissions fall fast, reach net zero, and then decline, the risk of a future AMOC collapse doesn’t vanish.

Some studies point to a shutdown within decades. Others suggest the system limps along in a weakened state, aided by Southern Hemisphere wind patterns.

The Utrecht-led analysis doesn’t overturn those findings. It adds nuance about the sequencing of freshwater from both ice sheets and argues that Greenland and West Antarctica are intertwined in the same global circulation.

Models can’t capture everything

As always with modeling, assumptions matter. The timing and size of melt pulses hinge on how quickly the ice sheets disintegrate.

This depends on ocean heat nibbling at glacier fronts, atmospheric warming, and internal ice feedbacks.

The simulations also simplify or omit feedbacks such as wind-driven changes over the Southern Ocean that reshape sea ice cover, alter heat uptake, and change where dense waters form around Antarctica. Those processes, in turn, can reverberate through the overturning.

The urgent need to cut emissions

Rapid emissions cuts remain the only reliable way to ease pressure on both ice sheets, and by extension the AMOC. Every tenth of a degree avoided reduces freshwater forcing and slows sea-level rise.

Second, adaptation should assume a weaker conveyor, not a stable one: Europe needs plans for sharper winter extremes and altered rainfall.

Atlantic coasts should budget for higher regional sea levels than the global mean. And drought-sensitive regions must prepare for longer dry spells.

Third, vigilance matters. Sustained monitoring of temperature, salinity, currents, sea ice, and ice-sheet mass will be essential to spot shifts early and ground-truth models.

Action remains the only path

This study suggests there’s a pathway in which early, massive West Antarctic freshening nudges the AMOC away from a full collapse and shortens its painfully long road back.

However, that doesn’t help much on the timelines that matter to societies. The circulation still weakens dramatically, and the “rescuer” brings devastating sea-level rise.

The sensible response is not to hope the south saves the north, but to cut emissions quickly while hardening coasts, retooling energy systems, and adapting food and water management to a century in which the oceans themselves are changing the rules.

The study is published in the journal Science Advances.

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