A major ocean current system that helps keep Ireland’s climate mild may be weakening – but perhaps not as drastically as once feared, according to a new study from the California Institute of Technology (Caltech).

The Atlantic Meridional Overturning Circulation (AMOC), often likened to a giant conveyor belt in the ocean, moves warm water from the tropics northward and plays a pivotal role in shaping the climate of Europe and the North Atlantic region. For Ireland, this current helps temper winters and contributes to the relatively mild, wet climate that defines much of the country.

For years, scientists have warned that global warming could significantly weaken the AMOC, triggering a cascade of regional climate shifts. In worst-case scenarios, northern Europe – including Ireland – could face a sharp drop in temperatures, while parts of the Amazon and West Africa could become drier. Some climate models have even predicted a near-collapse of the AMOC later this century.

However, the new research published in Nature Geoscience offers a more reassuring outlook. Using a simplified but robust model grounded in real-world ocean measurements collected over the past two decades, the Caltech team found that the AMOC will likely weaken by 18% to 43% by 2100 – a notable decline, but far less severe than many earlier projections.

“This is still a weakening, and it still matters, especially for regions like Ireland that are directly affected by Atlantic circulation,” says lead author Dave Bonan. “But the results suggest we may avoid the most catastrophic scenarios.”

What This Means for Ireland

Ireland’s relatively warm winters – unusual for a country at its latitude – are partly due to the AMOC’s influence. A significant slowdown in this current could bring colder winters, more frequent storms, and disruptions to marine ecosystems. Some research has even suggested a weakening AMOC could increase sea levels around Ireland’s coast.

While the new study downplays the likelihood of a full collapse, the projected weakening could still affect Irish weather patterns and fisheries, and potentially exacerbate extreme weather events.

“This doesn’t mean we’re out of the woods,” says Professor Andrew Thompson, co-author and environmental science expert at Caltech. “Even modest changes to the AMOC can have outsized regional impacts.”

A New Approach to Climate Modelling

The researchers say previous climate models may have overestimated the potential for AMOC collapse because of how they simulate ocean layers and density. The Caltech team focused on the physical mechanics driving the current – particularly how changes in temperature and salinity impact the depth and strength of the AMOC.

They discovered that climate models with deeper present-day AMOCs tend to show more extreme weakening under global warming. But many of these models may not accurately reflect how the ocean works today. By anchoring their model to actual observational data, the team was able to narrow the range of uncertainty and provide a more grounded projection.

“This work helps reconcile conflicting climate predictions and offers a clearer picture of the AMOC’s future,” says co-author Tapio Schneider.

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