For years the slowdown of the AMOC remained above all a climate prediction, something that appeared in the mathematical models, simulations and graphs used to imagine the future of the planet. This time, however, the message comes directly from the ocean. Silent, slow, accumulated over time. And for this reason much more difficult to ignore.
A group of researchers from University of Miami Rosenstiel School collected nearly two decades of measurements along the western margin of the North Atlantic. We are not talking about satellites or floating buoys, but about instruments fixed to the seabed, over a thousand meters deep, capable of recording pressure, water density, temperature and movement of currents year after year.
The result shows a persistent weakening of the AMOC, the great ocean circulation that transports warm water northward and cold water southward into the depths of the Atlantic. A kind of gigantic marine conveyor belt that redistributes heat between the tropics and Europe and helps stabilize climate, precipitation and sea levels. The study was published in the journal Science Advances.
What is AMOC and why does it matter so much?
The Atlantic Meridional Overturning Circulation, abbreviated to AMOC, is one of the most important climate mechanisms on the planet. It works thanks to a very delicate balance: warm, salty surface water rises towards the North Atlantic, releases heat into the atmosphere, cools, becomes denser and sinks. From there it slowly returns southward as a deep current.
It is this continuous movement that helps Europe have a relatively mild climate compared to other areas at the same latitude. Without this circulation, many areas of the continent would have much harsher winters.
But when the system loses strength, the effects ripple far beyond the ocean. The paths of storms change, rainfall changes, the risk of extreme events increases and along part of the eastern coast of the United States the sea level can rise faster, because the current exerts less “traction” on surface water masses.
Shane Elipot, a physical oceanographer and senior author of the research, explained that a weaker AMOC can profoundly alter atmospheric patterns, affecting both precipitation and the frequency of more intense storms.
This time they are not simulations
The difference compared to many previous studies lies above all here: the researchers did not only work on theoretical projections. They compared data collected in four different areas of the Atlantic between the tropics and mid-latitudes, from about 16.5°N up to 42.5°N. In all sections analyzed the same pattern appeared: a progressive reduction in the flow of deep cold water.
An isolated anomaly can depend on a thousand temporary factors. However, when the same signal appears across such a large area of the ocean, the picture changes. It means something is moving on an ocean scale.
The scholars also highlight another important element: the western margin of the Atlantic could function as a sort of early warning system. That’s where the changes seem to emerge first with greatest clarity. Knowing where to observe allows you to improve monitoring and understand in advance how the climate system evolves.
A slowdown that has been expected for some time
The idea that the AMOC could weaken certainly does not arise today. For years, climate scientists have linked this risk to rising global temperatures and the melting of Greenland. Fresh water from the ice dilutes the salinity of the North Atlantic. And less salinity means less density. If the water struggles to sink, the entire mechanism loses efficiency.
The difficult point was to understand whether all this was already really happening or whether it was still confined to theoretical projections. This study does not close the question definitively, also because twenty years, for ocean times, remains a relatively short window. But it shifts the discussion to a different level: from possible scenarios to signals measured directly on the bottom of the Atlantic. And it’s a huge difference.
For hundreds of millions of people between Europe and the Americas this current continues to work in silence every day, regulating climate, rainfall, temperatures and tides without almost anyone really thinking about it. Oceanographers, however, are watching it very carefully. And the reason is starting to become quite clear.
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