Atlantic Ocean Currents Face Dramatic 50% Decline by End of Century, Study Finds
New research suggests that a vital system of Atlantic Ocean currents is on track for a far more significant slowdown than previously estimated, potentially reaching a 50% weakening by the year 2100.
The study, published in Science Advances, focuses on the Atlantic Meridional Overturning Circulation (AMOC), often described as a “conveyor belt” that transports warm water to the North Atlantic. While existing climate models have long predicted a decline, this new analysis indicates the weakening could be roughly 60% stronger than the average projections used by the Intergovernmental Panel on Climate Change (IPCC).
A Narrowing Window for Adaptation
The AMOC plays a critical role in regulating global climate. A substantial slowdown would have far-reaching consequences, including shifting weather patterns that could dry out the Sahel region in Africa, threatening food security.
Furthermore, changes to these currents influence regional temperatures, precipitation patterns, and the position of the jet stream, whilst also impacting marine ecosystems that rely on heat transport and deep-water formation.
Experts suggest that a collapse or severe weakening of this system could lead to more extreme winter weather in Europe and a significant rise in sea levels along the North American coast.
Addressing Model Biases
Researchers from the University of Bordeaux reached these conclusions by applying a specialised statistical method, ridge-regularised linear regression, to correct known biases in current climate models. A primary discovery was that many existing models suffer from a “fresh bias” in the South Atlantic, meaning they underestimate the saltiness of the water.
Since salt and temperature drive the density that keeps the “conveyor belt” moving, these models likely overestimate the AMOC’s stability. By correcting for this South Atlantic salinity bias, the researchers found the system is likely much closer to a “tipping point” than previously thought.
Regional Drivers of Change
The research identifies two primary groups of regional variables that account for the majority of the correction to future projections. Approximately 47% of the projection correction is linked to sea surface salinity in the South Atlantic.
Additionally, roughly 36% of the correction is driven by sea surface temperatures in the subtropical North Atlantic, the subpolar East, and the Nordic Seas. In the Labrador Sea, models also tend to underestimate salinity; correcting this further confirms a more significant future slowdown, as higher salinity typically leads to stronger deep-water convection.
Innovation in Statistical Modelling
To reach these conclusions, the researchers employed ridge-regularised linear regression, a method more common in health and economic sciences than in climatology. This approach was chosen for its ability to manage multiple correlated variables simultaneously, which is necessary for a system as complex as Atlantic currents.
By using a “perfect model” approach to validate the findings, the team was able to reduce model uncertainty, the discrepancies between different climate simulations, by 79%, providing a much more precise estimate than standard averages.
Refining Future Projections
Standard multimodel averages previously suggested a weakening of approximately 32% by the end of the century. However, when constrained by real-world observations, the new estimate jumps to approximately 51%.
The study also highlights that by the year 2100, 78% of the uncertainty in these projections comes from the differences between the climate models themselves, rather than the specific emission scenario or natural internal variability.
This emphasises that integrating multiple types of ocean data provides a much clearer, albeit more concerning, picture of the Atlantic’s future and the urgent need for refined adaptation strategies.
