A Major Atlantic Ocean Current May Be Weakening Faster Than Expected — Here’s What That Could Mean
The Atlantic Southerly Overturning Circulation (AMOC) may be weakening at a much faster rate than previously thought, with new research predicting a slowdown of more than 50% by the end of the century.
This could bring us closer to a dangerous tipping point that could trigger a cascade of environmental changes, from severe cold snaps in Europe to droughts in the Sahel and extreme weather events.
By integrating observation constraints, researchers writing in Scientific advances attempted to reduce the uncertainty inherent in most models to date and produce a more realistic projection of AMOC weakening.
What is AMOC?
The AMOC, or Atlantic Meridional Overturning Circulation, is a vast system of ocean currents transporting water around the world, much like a conveyor belt or the interstate highway system. Warm, salty water moves northward along surface currents, bringing milder climates to northern Europe, before cooling, sinking, and returning southward along deep-water currents.
Although there is general consensus that the AMOC is likely to weaken over the course of this century, there is debate and uncertainty over exactly how much it will weaken and over what time frame, with different climate models producing very different predictions.
Learn more: About 12,900 years ago, a series of volcanic eruptions could have triggered a sudden ice age
Reduce levels of uncertainty
According to the paper’s authors, most of this uncertainty can be attributed to the climate models themselves. To try to reduce uncertainty, the team tested four observation constraint methods combining CM1P6 climate models with actual observations of at least one directly measurable variable.
Of the four methods, the ridge-regularized linear model approach proved to be the most effective, reducing inter-model spread by 79 percent and allowing researchers to account for 19 variables.
According to its estimates, the AMOC will be around 51% weaker by 2100 than its average between 1850 and 1900 – a result that would be considered a “substantial weakening of the AMOC” by the Intergovernmental Panel on Climate Change (IPCC). It is also about 60 percent higher than the average predictions of climate models.
The researchers highlight two variables in particular: sea surface temperatures in the subtropical region and sea surface salinity in the South Atlantic. Temperature and salinity affect the buoyancy and density of water and, in turn, influence the formation of deep water.
The paper’s authors attribute the improvement in model certainty to “the correction of a bias in South Atlantic surface salinity.” But while they see improvements, the researchers also note that other variables, like the melting of the Greenland ice sheet, are not included in climate models and could influence predictions.
Rely on climate models
Jochem Marotzke, director of the Max Planck Institute for Meteorology, who was not involved in the study, called the study thorough and well done:
“This study illustrates one point very clearly: a more realistic and higher surface salinity in the South Atlantic leads to a greater weakening of the AMOC. I can very well imagine that this relationship will also be true for higher models of the future.”
But Marotzke also explained that researchers have no choice but to rely on climate models that struggle to properly simulate the fluid dynamics of the AMOC.
“It remains an open question whether the reduction in model deviation described in the paper actually reduces real uncertainty,” Marotzke said. Discover. “We are far from having a reliable understanding of the fundamentals of AMOC variability and change.”
“We need to move away from the current unrealistic ocean dynamics in most climate models and simulate the ocean in its true turbulent nature, as part of climate simulations,” Marotzke added.
What would a weakening of the AMOC mean in practice?
The AMOC plays a key role in climate regulation, bringing warm water and a milder climate to parts of Western Europe located at the same latitude as Canada. A weakening – or, in the worst case, a collapse – of the AMOC could cause temperatures in Europe to plummet. According to a 2024 study in Scientific advancesin modeled collapse scenarios, the continent could experience “very strong and rapid cooling” of more than 5.4°F (3°C) per decade.
More broadly, it could change precipitation patterns and storm activity around the world and increase the frequency of extreme weather events, according to the UK’s National Oceanography Center.
Learn more: About 34 million years ago, Earth’s most powerful ocean current emerged and reshaped the climate
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