Cold spot in the Atlantic could signal big trouble for global climate

For over 100 years, the North Atlantic has hosted an anomaly. South of Greenland lies a patch of cool ocean water. This region, called the North Atlantic Warming Hole (NAWH), defies global warming.

Scientists long debated its cause. A new study now shows that the weakening of a vital ocean current – the Atlantic Meridional Overturning Circulation (AMOC) – explains it best.

“People have been asking why this cold spot exists,” said climate scientist Wei Liu. “We found the most likely answer is a weakening AMOC.”

Source of the Atlantic cold spot

The AMOC moves warm, salty water northward and cooler water southward. This system shapes climate across continents. When it slows, less heat and salt reach the north. The result? Cooler, fresher waters south of Greenland.

Liu and Kai-Yuan Li from University of California Riverside studied temperature and salinity data spanning a century.

Direct AMOC measurements only cover 20 years. But using six long-term sea surface temperature (SST) datasets and three salinity datasets, the researchers built a much clearer picture. They also tested 94 global climate models.

Only models simulating a slowing AMOC recreated the observed North Atlantic cooling. These models showed trends of up to −0.3 °C per century (about −0.54 °F per century), matching the real-world pattern known as the NAWH.

Clear signs of AMOC weakening

The team defined AMOC fingerprints using a dipole pattern: cooling in the subpolar gyre (south of Greenland) and warming near the Gulf Stream. This contrast, visible in SST and salinity (SSS), offers a reliable way to track AMOC strength.

From the observations, they estimated that the AMOC weakened by −1.01 to −2.97 Sverdrups per century from 1900 to 2005.

A single Sverdrup equals one million cubic meters of water per second. That’s a massive loss of energy transport across the Atlantic.

Atlantic cold spot reaches the deep ocean

The cooling and freshening do not stop at the surface. The study reveals that subsurface waters down to 3,000 meters also exhibit clear signs of this trend.

The vertical profile shows cooling and freshening at depth, confirming that AMOC’s slowdown affects the entire ocean column.

Model comparisons between weakened and strengthened AMOC simulations highlighted another key point.

A slower AMOC causes a heat transport gap – less warm water moves northward. This creates a cold zone between 40°N and 65°N, which matches the NAWH location.

Long-term AMOC slowdown confirmed

Salt transport in the North Atlantic also changes. A weakened AMOC means more freshwater sits at the surface. This freshening was strongest across the NAWH and extended to the Labrador Sea.

While observations showed some salinity increase in the Labrador Sea, models still closely captured the broad trend.

Both the SST- and SSS-based fingerprint indices (FPISST and FPISSS) showed strong correlation with AMOC weakening. These patterns help researchers verify the slowdown, even without direct current measurements.

Other theories on North Atlantic cold spot

Some past theories suggested the NAWH came from changes in wind patterns or reduced air pollution. These theories were tested in the new study.

In experiments with slab-ocean models (which isolate atmospheric effects), the cooling did not appear. Only in fully coupled models – with real ocean circulation – did the NAWH form.

“We tested CO₂ experiments in slab-ocean and fully coupled models,” the authors wrote. “Only the fully coupled models with a weakening AMOC showed the cooling feature.”

A broader climate concern

The South Greenland anomaly in the North Atlantic affects more than just temperature. It reshapes the jet stream and alters weather across Europe and North America.

The cold zone also threatens marine ecosystems. Many fish species rely on certain salinity and temperature levels. Disruptions could shift where they live, breed, and migrate.

“Our results show that only the models with a weakening AMOC get it right. That means many of the recent models are too sensitive to aerosol changes, and less accurate for this region,” noted Liu.

Looking ahead with better tools

This study helps improve climate forecasts by identifying the most realistic models. It also highlights the value of indirect evidence. Fingerprints built from ocean temperature and salinity can track changes even when direct measurements are sparse.

“We don’t have direct observations going back a century, but the temperature and salinity data let us see the past clearly,” Li noted.

If greenhouse gas emissions keep rising, the AMOC may continue to weaken. That means more pronounced cooling near Greenland and stronger climate impacts across Europe.

By understanding this cold patch, scientists gain a clearer view of Earth’s climate system. The North Atlantic Warming Hole is not a mystery anymore. It’s a sign – quiet, persistent, and measurable – of a changing ocean current that affects us all.

The study is published in the journal Communications Earth & Environment.

Image description: The ocean anomaly map reveals the Atlantic sea surface temperature trend between 1900-2005 (color shading in °C) for the average of six observation datasets. 

Image Credit: Kai-Yuan Li/UCR

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