For decades, a strange patch of cold water south of Greenland has defied the Atlantic Ocean’s overall warming, baffling scientists and sparking fierce debate. Now, new research reveals the culprit: a dramatic slowdown of the mighty ocean currents that shape our climate, with consequences that reach far beyond the Arctic Circle.
Key Points at a Glance
- The persistent cold spot south of Greenland is caused by the weakening Atlantic Meridional Overturning Circulation (AMOC).
- AMOC acts as a “conveyor belt,” transporting warm, salty water north and cooler water south at depth, shaping weather and climate.
- Researchers matched 100 years of ocean temperature and salinity data with nearly 100 climate models, finding only those with a weakening AMOC could reproduce the cold spot.
- This slowdown could alter rainfall, shift the jet stream, and disrupt marine ecosystems across Europe and North America.
The Atlantic Ocean is heating up, but not everywhere. For more than a century, a curious anomaly has persisted: a stubborn cold patch south of Greenland that stands out like a bruise in the North Atlantic’s warming waters. Scientists have debated whether pollution, shifting winds, or hidden ocean processes might be to blame. Now, an international team led by climate scientist Wei Liu at the University of California, Riverside, has cracked the case. Their research points squarely to a weakening in one of Earth’s most powerful climate engines—the Atlantic Meridional Overturning Circulation, or AMOC.
The AMOC is the giant “conveyor belt” of the Atlantic, moving warm, salty water from the tropics northward and returning cooler water south at depth. It’s a system so immense that it helps regulate temperatures, rainfall, and even the position of the jet stream across two continents. When the current is strong, it delivers a steady stream of heat to the North Atlantic. But as the new study shows, that conveyor belt has been slowing for more than a century—transforming the region south of Greenland into a rare “cold spot” in a world that’s otherwise heating up fast.
How do scientists know? The key is in the water itself. Ocean temperatures and salinity—how salty the water is—are both fingerprints of how much heat and salt are being carried north. Liu and doctoral student Kai-Yuan Li combed through a century’s worth of these records, using them like detective clues to reconstruct how the AMOC has changed. Since direct measurements of AMOC strength only go back about 20 years, this long-term data is invaluable. By comparing observations to nearly 100 different climate models, they found a clear match: only the models with a weakening AMOC could reproduce the observed cooling south of Greenland and the drop in salinity there. Models that assumed a stronger current failed entirely.
“It’s a very robust correlation,” explains Li. “If you look at the observations and compare them with all the simulations, only the weakened-AMOC scenario reproduces the cooling in this one region.” This discovery helps resolve a simmering debate among climate scientists: some had argued that recent aerosol pollution or changes in the atmosphere were the cause, but these theories just didn’t fit the real-world data.
The implications go far beyond a cold patch of water. The region south of Greenland is one of the most sensitive on the planet to shifts in ocean circulation. When the AMOC weakens, less warm, salty water reaches the sub-polar North Atlantic. This not only cools the surface waters, but also leads to decreased salinity, which can have ripple effects on marine ecosystems, fisheries, and the very weather patterns that shape daily life across Europe and North America.
The changes can shift the jet stream—the high-altitude air current that steers storms across the Atlantic—altering rainfall and temperatures. Wetter winters in southern Europe, drier spells in the north, and disruptions to the breeding grounds of vital fish species may all be linked to this single, stubborn cold spot and its slow-moving parent current.
Perhaps most worrying, the research shows the AMOC’s decline isn’t just a blip. The weakening has lasted over a century, and there’s little sign it will reverse soon, especially if greenhouse gas emissions keep rising. If the trend continues, scientists warn of even bigger changes ahead, from shifts in hurricane tracks to unpredictable seasons and further stress on the ocean’s delicate balance.
Yet there is hope in knowledge. By pinpointing the cause of the South Greenland anomaly, scientists can improve climate models and forecasts, helping governments, communities, and industries prepare for a changing world. As Li puts it, “We don’t have direct observations going back a century, but the temperature and salinity data let us see the past clearly. This work shows the AMOC has been weakening for more than a century, and that trend is likely to continue if greenhouse gases keep rising.”
As the climate system evolves, the Atlantic cold spot could grow in influence, its icy waters serving as a warning beacon for the world. Understanding its origins isn’t just a scientific victory—it’s a crucial step in adapting to and mitigating the impacts of global change. The ocean, as always, holds the keys to our climate’s future.
Source: University of California, Riverside
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