Scientists have issued a stark warning that a critical Atlantic current system is far more likely to collapse than previously estimated, posing severe risks to global climate stability. A new study, published in the journal Science Advances, indicates that the Atlantic meridional overturning circulation (Amoc) could experience a slowdown of 42% to 58% by 2100, a level that almost certainly leads to a catastrophic collapse.
Alarming Findings on Ocean Circulation
The Amoc is a major component of the global climate system, responsible for transporting sun-warmed tropical waters to Europe and the Arctic, where it cools and sinks to form a deep return current. Research confirms that this circulation is already at its weakest point in 1,600 years due to the ongoing climate crisis. By combining real-world ocean observations with climate models, scientists have significantly reduced uncertainty, revealing that the most pessimistic predictions are, unfortunately, the most accurate.
Potential Global Consequences
A collapse of the Amoc would have devastating effects worldwide. It could shift the tropical rainfall belt, disrupting agriculture for millions of people, plunge western Europe into extreme cold winters and summer droughts, and add 50-100cm to rising sea levels around the Atlantic. Dr Valentin Portmann, lead researcher at the Inria Centre de recherche Bordeaux Sud-Ouest in France, stated, "We found that the Amoc is going to decline more than expected compared to the average of all climate models. This means we have an Amoc that is closer to a tipping point."
Expert Concerns and Historical Context
Professor Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research in Germany, who has studied the Amoc for 35 years, expressed deep concern over the findings. "This is an important and very concerning result. It shows that the 'pessimistic' models, which show a strong weakening of the Amoc by 2100, are, unfortunately, the realistic ones," he said. Rahmstorf added that the chance of an Amoc shutdown now appears to exceed 50%, compared to earlier estimates of around 5%, highlighting that the most dramatic climate changes in Earth's history have occurred when the Amoc shifted states.
Mechanisms Driving the Slowdown
The weakening of the Amoc is primarily driven by rapid Arctic warming due to global heating, which slows ocean cooling and reduces water density. This creates a feedback loop where increased rainfall freshens surface waters, further impeding the sinking process. The study utilized innovative methods like ridge regression to assess models, focusing on surface salinity in the south Atlantic, which enhanced the credibility of the predictions.
Future Projections and Additional Risks
While precise predictions remain challenging due to the Amoc's complexity and natural variations, scientists warn that a major weakening is now expected. Rahmstorf noted that current models may even underestimate the risk, as they do not account for meltwater from the Greenland ice cap, which could exacerbate the slowdown. He emphasized, "I now am increasingly worried that we may well pass that Amoc shutdown tipping point, where it becomes inevitable, in the middle of this century, which is quite close."
This research underscores the urgent need for climate action to prevent irreversible damage, with experts urging that avoiding an Amoc collapse must be prioritized "at all costs" to safeguard global ecosystems and human societies.
