A new study examines the one region on Earth that has cooled, not warmed, in recent years. Researchers say the 'cold blob' is closely tied to the Atlantic Meridional Overturning Circulation, AMOC.
In the North Atlantic, south of Greenland, lies the so‑called “Cold Blob”, a mysterious patch of cold that is considered the only place on Earth where temperatures have actually fallen over the past few decades.
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A team led by Prof Dr Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research (PIK) has now published a new study on the “warming hole” in the Atlantic Ocean in the journal “Geophysical Research Letters (source in German)”.
Based on an analysis of temperature data sets from measurements in the North Atlantic, the researchers conclude that changes in heat transport within the ocean are the main driver behind the Cold Blob.
The scientists write: “This is a cause for concern, since any further weakening of Atlantic heat transport in the course of future climate change could have severe impacts on the climate and weather conditions in Europe and other parts of the world.”
Last February, the Nordic Council – comprising Denmark, Iceland, Norway, Sweden and Finland, with Åland, the Faroe Islands and Greenland as associate members – warned that winter temperatures in Iceland could fall to as low as minus 45 degrees Celsius. The island would then be completely encircled by ice – for the first time since the Viking era.
Why AMOC matters
Scientists have long been worried about the weakening of the so‑called AMOC. AMOC stands for “Atlantic Meridional Overturning Circulation”, a vast system of ocean currents. It carries warm water northwards along the surface of the Atlantic and cold water southwards along the ocean floor. It is one of the planet’s key systems for redistributing heat.
“Our analysis supports the interpretation of the observed Cold Blob as a sign of a weakening AMOC, which makes a major contribution to lateral heat transport into this subpolar gyre region,” the new study from the Potsdam Institute for Climate Impact Research states.
Previous research into episodes of dramatic cooling in Europe over the past 100,000 years suggests that melting ice sheets could weaken the AMOC by altering the salinity and temperature of seawater.
Freshwater reduces salinity – and thus the density of the water – at the ocean surface. That means less surface water sinks, which can slow down the current.
Is the world nearing the tipping point?
For years, research teams have been trying to determine when the tipping point of the Atlantic Meridional Overturning Circulation (AMOC) might be reached – a shift that, amid global warming, would trigger dramatically colder winters in northern Europe.
In the event of an AMOC collapse, sea levels along the US east coast would rise rapidly, as the current normally drives water away from the land. Storms in the Atlantic would become more intense. But for now, projections remain highly uncertain.
Around 12,500 years ago – during the last major cold spell, the Younger Dryas – it took about 100 years for the AMOC to become fully operational again. Temperatures in Greenland needed around 40 years to recover from the extreme glacial conditions.
The authors of the latest study speak of “early warning signals” that ocean circulation is approaching a tipping point, as well as of “clear evidence of a weakening AMOC”. They write that “this risk requires urgent attention from political decision-makers”.
