That cold isn't a get-out-of-jail-free card in terms of global warming.
In the North Atlantic, a paradox has taken shape: a patch of ocean that refuses to warm is making Europe hotter. The so-called 'cold blob' south of Iceland, born partly from Greenland's melting ice, distorts the jet stream in ways that trap scorching heat over the continent — a reminder that climate disruption does not move in straight lines. Beneath this surface irony lies a deeper concern, as scientists now read the cold blob as a possible symptom of a slowing Atlantic circulation system whose stability has underpinned human civilization's climate for thousands of years.
- A counterintuitive chain reaction is unfolding: the colder the North Atlantic grows, the more ferociously heat accumulates over Europe, as the jet stream bends away and high-pressure domes lock in place.
- Greenland's accelerating ice melt is feeding the anomaly, pouring freshwater into the ocean and deepening a cold patch that has cooled 0.9°C even as global seas warmed by a full degree since 1900.
- Computer simulations and observational studies now confirm the cold blob is not a passive bystander — it is actively lengthening and intensifying European heatwaves, with direct health consequences for millions across the continent.
- The cold blob may be more than a weather curiosity: leading researchers now read it as evidence that the Atlantic Meridional Overturning Circulation — the great ocean conveyor belt regulating planetary heat — is measurably slowing.
- Scientists once divided on the risk of AMOC collapse are shifting their assessments, with prominent researchers now placing the odds above 50% this century, warning of severe winters, widespread drought, and rising seas as potential consequences.
A stretch of the North Atlantic south of Iceland has been cooling for over a century, defying the global trend by dropping nearly a degree Celsius while the rest of the world's oceans warmed. Scientists call it the 'cold blob,' and far from offering any relief from climate change, it appears to be making Europe's heatwaves worse.
The mechanism is counterintuitive. When this cold patch meets warmer surrounding waters, the sharp contrast warps the jet stream, causing it to slow and bend northward rather than sweep cleanly across the continent. The result is a heat dome — a stubborn high-pressure system that parks over Europe and traps hot air in place. Research by Marilena Oltmanns at the University of Bremen traced the chain directly to Greenland ice melt, whose freshwater runoff cools the North Atlantic surface and guides winds in ways that concentrate heat over land. Simulations confirmed the effect: with the cold blob present, European heatwaves grow longer and more severe. As oceanographer Gerard McCarthy put it, a cold Atlantic is no escape from warming — some extremes are actually made worse by it.
The deeper alarm is what the cold blob may represent. Stefan Rahmstorf of the Potsdam Institute, once skeptical of catastrophic risk, now believes the blob is caused by the Atlantic Meridional Overturning Circulation — the vast conveyor belt of currents that distributes heat across the planet — delivering less warmth to the region, a sign the system itself is slowing. He now estimates more than a 50 percent chance of AMOC collapse this century, with consequences that would reach far beyond Europe: harsher winters across the north, droughts in South Asia and Africa, and rising seas along the North Atlantic coast.
What began as a scientific curiosity has become a warning. The cold blob is real, its effects on European heat are measurable, and it may be an early signal of a far larger unraveling in the ocean systems that have kept the climate livable for millennia.
A patch of cold ocean water south of Iceland and Greenland has become an unlikely architect of Europe's most punishing heatwaves. The paradox is stark: while the planet warms, this stretch of the North Atlantic has cooled, bucking the global trend by as much as 0.9 degrees Celsius since 1900, even as worldwide sea surface temperatures rose by a full degree. Scientists call it the "cold blob," and recent research suggests it may be doing far more than simply sitting there—it may be actively intensifying the extreme heat that has been searing the continent.
The mechanism is counterintuitive but increasingly well documented. When cold and warm waters collide, the sharp temperature contrast reshapes the air above them, warping the jet stream that normally flows west to east across Europe. The jet stream becomes wavier and slower, bending northward around the continent instead of crossing it. This atmospheric distortion creates the conditions for a "heat dome"—a high-pressure system that parks itself over Europe and traps scorching air in place. A 2024 study led by Marilena Oltmanns, an ocean and climate physicist at the University of Bremen, traced the chain of causation: Greenland ice melt pours freshwater into the ocean, creating colder surface waters in the North Atlantic. That cold anomaly then acts as a guide for winds and the jet stream, bending them northward and allowing heat to accumulate over Europe. Computer simulations run in 2023 by researcher Sabine Bischof at Germany's GEOMAR Helmholtz Centre for Ocean Research Kiel showed the effect directly—with the cold blob present, European heatwaves became both longer and more intense.
Gerard McCarthy, an oceanographer at Ireland's Maynooth University, put it plainly: a cold Atlantic does not mean a colder Europe. "That cold isn't a kind of a get-out-of-jail-free card in terms of global warming," he said. "Some of the hot extremes can actually be exacerbated by this cold blob in the Atlantic." A 2016 study had already suggested that cold Atlantic anomalies were a common precursor to major European heatwaves dating back to the 1980s. The pattern had become unmistakable.
But the cold blob signals something potentially far more consequential than the current summer's heat. It may be a warning sign that the Atlantic Meridional Overturning Circulation—the AMOC, a vast conveyor belt of ocean currents that regulates the planet's climate—is weakening. The AMOC carries warm tropical waters northward to the Northern Hemisphere, where they cool, become denser, and sink before returning southward at depth. This circulation is fundamental to how Earth distributes heat. Research published last month sought to resolve a scientific debate about what was causing the cold blob. Stefan Rahmstorf, head of Earth system analysis at the Potsdam Institute for Climate Impact Research, led the study and found that the cold blob was caused by ocean currents bringing less heat into the region, not by more heat escaping from the surface. In other words, the AMOC itself was slowing.
Rahmstorf's conclusion carries weight because he was once skeptical of the risk of an AMOC shutdown. He has changed his mind. He now estimates there is more than a 50 percent chance of a collapse happening this century. "I am very worried," he said. "The consequences of an AMOC shutdown would be massive in many parts of the world." Those consequences would include harsher winters across northern Europe, droughts in South Asia and parts of Africa, and rising sea levels around the North Atlantic. Scientists broadly agree the AMOC is weakening as the planet warms, though debate continues over how quickly it could slow and whether a full collapse is truly possible within a hundred years. What is no longer in question is that the cold blob is real, that it is intensifying European heat right now, and that it may be a symptom of a much larger disruption to the ocean systems that have kept the climate stable for millennia.
Citas Notables
That cold isn't a kind of a get-out-of-jail-free card in terms of global warming. Some of the hot extremes can actually be exacerbated by this cold blob in the Atlantic.— Gerard McCarthy, oceanographer, Maynooth University
I am very worried. The consequences of an AMOC shutdown would be massive in many parts of the world.— Stefan Rahmstorf, Potsdam Institute for Climate Impact Research
La Conversación del Hearth Otra perspectiva de la historia
How does cold water in the Atlantic make Europe hotter?
The cold blob changes the shape of the jet stream. When cold and warm water meet, the temperature contrast warps the air above them, making the jet stream wavier and slower. Instead of crossing Europe, it bends northward around it. That allows heat to get trapped over the continent.
So the cold blob is actually making the heatwaves worse?
Yes. Studies show that when the cold anomaly is present, European heatwaves become longer and more intense. It's not a buffer against warming—it's an accelerant.
What's causing the cold blob to exist in the first place?
Greenland ice is melting and pouring freshwater into the ocean. That freshwater makes the surface waters colder. But the deeper cause is that ocean currents are bringing less warm water into the region than they used to. The AMOC—the Atlantic circulation system—is slowing down.
And that's the real concern?
Exactly. The cold blob is a symptom. If the AMOC collapses entirely, the consequences would be severe: much harsher winters in northern Europe, droughts in South Asia and Africa, rising sea levels. One leading scientist now gives it a better than 50-50 chance of happening this century.
Why did he change his mind?
The evidence accumulated. The cold blob is real, it's intensifying heat waves, and the data shows it's caused by weakening ocean circulation, not by surface heat loss. Once you see that chain of causation, you can't unsee it.
So we're watching the climate system destabilize in real time?
We're watching one of its critical mechanisms slow down. Whether it collapses or stabilizes at a new equilibrium—that's still an open question. But the trajectory is clear.