Atlantic Ocean's hidden conveyor belt system could shut down by 2025

Scientists calculate a 95 percent chance the AMOC— a crucial system of ocean currents— will collapse mid-century. What will happen then?
Sade Agard
What is the AMOC? And what happens when it collapses?
What is the AMOC? And what happens when it collapses?

Henrik Egede-Lassen / Zoomedia

The Atlantic Meridional Overturning Circulation (AMOC) — a crucial system of ocean currents that transport warm waters northward in the North Atlantic — could collapse as early as 2025 if greenhouse gas emissions persist, according to a recent study published in Nature Communications on July 25.

The discovery highlights the significant impact of human activities on our planet's climate system.

What is the AMOC?

The AMOC is responsible for transporting warm, surface waters from the tropics to higher latitudes in the North Atlantic, where the water releases heat to the atmosphere, influencing regional climate and weather patterns.

As the warm water cools, it becomes denser and sinks to deeper ocean layers, forming a deep southward flow known as the North Atlantic Deep Water (NADW). This deep circulation returns water to the Southern Hemisphere, completing the overturning loop.

The AMOC is crucial to Earth's climate system, redistributing heat and regulating temperatures. It's considered one of the planet's key tipping elements, with the ability to shift into an irreversible state.

The potential collapse of the AMOC is a significant concern as it would severely impact the climate, not only in the North Atlantic region but also worldwide. Such an event could affect regional temperatures, sea ice, weather patterns, as well as the distribution of nutrients and marine ecosystems.

A similar abrupt climate change occurred during the last ice age, known as the Dansgaard-Oeschger events. The collapse and restoration of the AMOC caused these events.

The Dansgaard-Oeschger events had significant impacts on the Earth's climate. They led to rapid and dramatic shifts in temperature, causing sudden warming followed by gradual cooling over relatively short periods, typically lasting a few decades.

10-15°C temperature changes

They led to the Northern Hemisphere experiencing drastic temperature swings of 10-15 degrees Celsius within just a decade. This is much more significant than the changes of 1.5 degrees in a century.

Peter Ditlevsen and Susanne Ditlevsen studied sea surface temperatures in the North Atlantic from 1870 to 2020 as a proxy for AMOC. These records provide reliable information on temperature trends since they date back much further than direct AMOC measurements.

"We predict with high confidence the tipping [collapse] to happen as soon as mid-century (2025–2095 is a 95 percent confidence range)," the authors wrote in the study. 

"These results are under the assumption that the model is approximately correct, and we, of course, cannot rule out that other mechanisms are at play, and thus, the uncertainty is larger," they added. 

While the drivers behind the AMOC change were not investigated, the study demonstrates statistically that atmospheric CO2 concentrations have increased almost linearly within the period studied. 

The authors reasoned that they made their analysis as straightforward and solid as possible, minimizing assumptions. Considering the AMOC's significance for the climate system, they stress that clear signs of a potential collapse should not be ignored.

The full study was published in Nature on July 25 and can be found here

Study abstract:

The Atlantic meridional overturning circulation (AMOC) is a major tipping element in the climate system and a future collapse would have severe impacts on the climate in the North Atlantic region. In recent years weakening in cir- culation has been reported, but assessments by the Intergovernmental Panel on Climate Change (IPCC), based on the Climate Model Intercomparison Project (CMIP) model simulations suggest that a full collapse is unlikely within the 21st century. Tipping to an undesired state in the climate is, however, a growing concern with increasing greenhouse gas concentrations. Predictions based on observations rely on detecting early-warning signals, primarily an increase in variance (loss of resilience) and increased autocorrelation (critical slowing down), which have recently been reported for the AMOC. Here we provide statistical significance and data-driven estimators for the time of tipping. We estimate a collapse of the AMOC to occur around mid-century under the current scenario of future emissions.

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