Europe's Heatwave Has an Unlikely Accomplice: the Atlantic 'Cold Blob'

European Heatwave's Unlikely Accomplice: An Ocean 'Cold Blob'

A patch of cold ocean water south of Iceland and Greenland, known as the "cold blob," may be playing a significant role in the current heatwave affecting Europe. Despite the global warming trend, this region in the North Atlantic has cooled, and researchers believe it could be influencing weather patterns over the continent.

According to Gerard McCarthy, an oceanographer at Ireland's Maynooth University, a cold Atlantic doesn't necessarily mean a colder Europe. In fact, the cold blob can actually exacerbate hot extremes in Europe. McCarthy notes that some of the hot extremes can actually be exacerbated by this cold blob in the Atlantic.

The cold blob's connection to heatwaves in Europe has been explored in several studies. A 2016 study found that cold Atlantic anomalies were a common precursor to major heatwaves that had hit Europe since the 1980s. Another paper published in 2023 ran computer simulations with and without the cold blob, concluding that with this cold anomaly, we have longer and more intense heatwaves in Europe, according to Sabine Bischof, researcher at Germany's GEOMAR Helmholtz Centre for Ocean Research Kiel.

Marilena Oltmanns, an ocean and climate physicist, points to recent data showing a strong cold anomaly currently present in the subpolar North Atlantic, creating a front that acts like a guide for the winds and the jet stream. This can lead to a heat dome emerging over Europe, as the jet stream bends northward and flows northward around Europe instead of crossing it.

The cold blob is also linked to changes in atmospheric circulation, which can create conditions for high-pressure systems to park over Europe. This, in turn, can lead to more frequent and intense heatwaves. The melting of Greenland ice pours freshwater into the ocean, creating colder surface waters in the North Atlantic, which can influence the jet stream and lead to changes in weather patterns.

A recent study published last month sought to settle a scientific debate over whether the loss of heat from the sea surface or a weakening Atlantic Meridional Overturning Circulation (AMOC) were behind the cold blob. The study's lead author, Stefan Rahmstorf, found that the cold blob is caused by ocean currents bringing less heat into the region, rather than more heat lost through the sea surface.

The AMOC carries warm tropical waters to the Northern Hemisphere, where they cool, become denser, and sink before returning southward at depth. Scientists broadly agree that the AMOC is weakening with warming, but debate persists over how fast it could slow and whether a collapse is possible this century. A shutdown of the AMOC would have dire consequences, including tougher European winters, droughts in South Asia and parts of Africa, and higher sea levels around the North Atlantic.

Rahmstorf, head of Earth system analysis at the Potsdam Institute for Climate Impact Research, expressed concern about the potential consequences of an AMOC shutdown, stating that I am very worried and that the consequences of an AMOC shutdown would be massive in many parts of the world.