Stefan Rahmstorf tracks Cold Blob cooling south-east of Greenland
Scientists tracking the cold blob south-east of Greenland say the patch has cooled by as much as 1°C and now stands out as the only place on Earth that is cooling. Stefan Rahmstorf, a climate scientist at the Potsdam Institute for Climate Impact Research in Germany, and colleagues say the latest reanalyses point to the Atlantic Meridional Overturning Circulation transporting less heat.
The finding sharpens a long-running dispute over whether the warming hole is driven mainly by the atmosphere or by the ocean. Rahmstorf said, "Winds and clouds “only explain a modest fraction of the warming hole"."
Greenland cold blob cooling
The area south-east of Greenland has cooled since 1955, with heat loss from the ocean surface decreasing there and the ocean also cooling 1000 metres down. Rahmstorf and colleagues used climate reanalyses built from direct weather observations from satellites, buoys and ships, rather than only the 22 years of direct observation available for AMOC strength.
The cold blob, also known as the warming hole, appeared in a 2015 data visualisation using the 1951-80 temperature baseline. Over the past 150 years, Earth’s surface has warmed almost everywhere except this patch, which is why scientists are treating it as a possible sign of a broader circulation change rather than a local anomaly alone.
AMOC and Atlantic heat transport
The Atlantic Meridional Overturning Circulation carries warm, salty water from the Gulf of Mexico toward the north Atlantic, where it cools, sinks and returns south along the ocean floor. Scientists say fresh water from Greenland’s melting ice may be making that salty water less dense, and some research suggests the AMOC could cross a tipping point within decades.
Rahmstorf said, "Even if, in some modelling approaches, it seems possible that the cold blob is caused by the atmosphere, in fact, the data show it is caused by the ocean." He said the finding shows Atlantic Ocean circulation has already been changing for decades.
Arctic warming and competing studies
A 2022 study by Chengfei He and colleagues argued that rapid warming of the Arctic reduced the temperature difference between the pole and the tropics, shifted the jet stream northwards into the cold blob region and brought strong westerly winds that forced more evaporation and churned up the water. Another study said greater evaporation led to more clouds that shaded the cold blob from the sun’s warmth.
Rahmstorf’s team says those effects do not account for most of the pattern. Their reanalyses point to the ocean itself, which leaves the main question in a more specific place: whether the cooling patch is a short-term surface feature or a sign that the AMOC is already moving less heat.
Europe and monsoon risks
If the AMOC weakens further, scientists say Europe could cool and monsoon rains crucial for agriculture in Africa and Asia could be disrupted. The practical consequence for readers is that this is not just a map anomaly in the North Atlantic; it is one of the few visible signals scientists are using to judge whether a major circulation system is changing over time.
The next step is more observation, not a new calendar date. With only 22 years of direct AMOC measurements available, the pressure now falls on whether future data keep matching the cooling pattern south-east of Greenland.
