Atlantic Current in Crisis: New Warning Signal Predicts AMOC Collapse Within Decades

Redacción HC
02/07/2024

In the vast machinery of Earth’s climate, the Atlantic Meridional Overturning Circulation (AMOC) functions like a planetary engine—redistributing heat, influencing rainfall, and stabilizing sea levels. But a groundbreaking study published in Science Advances warns that this engine may be headed for failure. Using a physics-based early warning signal, researchers have identified a tipping trajectory that suggests the AMOC may collapse within decades—potentially triggering widespread climate disruptions.

This finding marks a pivotal advance: for the first time, a quantifiable, observable signal grounded in ocean physics offers a method to detect whether the AMOC is nearing its breaking point.

A Silent Crisis Brewing Beneath the Waves

For years, scientists have speculated that the AMOC could weaken or even shut down due to the influx of freshwater into the North Atlantic—primarily from melting glaciers and ice sheets. Such a collapse has occurred in Earth’s past and would drastically alter global weather patterns.

But until now, climate models lacked a reliable early warning indicator that could provide actionable lead time before collapse.

The team from Utrecht University, led by René van Westen and Henk Dijkstra, used the Community Earth System Model (CESM) to simulate a gradual “hosing” of freshwater into the North Atlantic. The result: a full collapse of the AMOC after 1,758 simulated years, with severe regional and global climate consequences.

How the Collapse Unfolds: A Physics-Based Timeline

Step 1: Triggering the Collapse

Researchers introduced a small but consistent increase in freshwater input (0.0003 Sv per year) into the Atlantic. Over time, this altered salinity gradients and weakened the AMOC’s deep-water formation process.

By year ~1758, the AMOC fully collapsed—producing:

• A 3°C per decade temperature drop in the North Atlantic
• Sea level rise of over 70 cm along Atlantic coastlines
• Disruption of the Intertropical Convergence Zone, altering rainfall in the Amazon and Sahel

The Smoking Gun: FₒᵥS as a Warning Signal

The real innovation lies in the discovery of FₒᵥS—a measure of the AMOC’s freshwater transport across 34°S. Roughly 25 years before the collapse, FₒᵥS hit a clear minimum, followed by a spike in variance.

“This kind of behavior is a hallmark of a system nearing a bifurcation,” explains van Westen. “It’s like hearing the brakes squeal before a car crashes.”

Traditional statistical signals, like sea surface temperature variance or autocorrelation, were less reliable and varied across regions. In contrast, FₒᵥS showed consistent and detectable changes, providing a physically grounded and geographically constrained indicator.

Connecting Models to Reality: Are We Already in Trouble?

Real-world ocean observations, particularly from the SAMBA array in the South Atlantic, already show declining values of FₒᵥS. Some projections suggest it could reach zero as early as 2075. If the Utrecht team’s findings are correct, that could mean the AMOC is on course to collapse within a generation.

This aligns with growing evidence from other studies, such as Ditlevsen et al. (2023), which also suggest that tipping points may be closer than expected.

However, the authors caution that model biases and missing feedbacks—such as ice–albedo effects or carbon cycle dynamics—mean exact timing remains uncertain. Yet the underlying physics of collapse remain robust, adding urgency to better monitoring.

Why It Matters: Beyond Climate Science

A collapse of the AMOC would trigger dramatic consequences across continents:

• Europe could face near-instant cooling and changes in agricultural viability.
• Atlantic coastal cities from New York to Recife could experience rapid sea level rise due to dynamic redistribution of water masses.
• Rainfall belts could shift, causing droughts in the Amazon and West Africa while flooding others.
• Global monsoonal patterns would destabilize, impacting food and water security for billions.

A Call to Action: Monitoring Before It’s Too Late

The research points to a clear policy priority: enhance oceanographic monitoring systems, especially for FₒᵥS at 34°S. Existing efforts like the SAMBA project must be expanded and sustained. Additionally:

1. Climate models should be adjusted for freshwater transport biases, especially in CMIP7.
2. Physical warning signals like FₒᵥS must be integrated into global climate early warning systems.
3. Policymakers must begin planning for worst-case scenarios—not decades from now, but within current strategic horizons.

“We now have the tools to see the collapse coming,” says Dijkstra. “What we need is the will to act on it.”

Conclusion: When Science Sounds the Alarm, Listen

This study marks a turning point in climate science. With a clear, physical early warning signal now identified, we are no longer blind to the threat of an AMOC collapse. The path forward requires rigorous observation, rapid policy coordination, and above all, a willingness to treat climate tipping points as real, near-term risks—not distant hypotheticals.

Topics of interest

Climate Biodiversity