Why a massive ‘cold blob’ in the Atlantic is putting scientists on edge

A cold blob in the Atlantic has left some scientists puzzled and others worried.

While most of the world’s oceans have steadily warmed over the past century, this region has cooled.

But what is it? Why are some puzzled and others worried?

Let’s take a closer look.

What is it?

The ‘blob’ is a patch of unusually cold ocean water in the North Atlantic, roughly between Greenland and Europe. Unlike the world’s oceans, this ‘blob’ has cooled by nearly 1°C since 1900, according to data reported by several outlets, including Nasa.

When it comes to global temperature maps, the cold blob looks like a patch of blue amid reds and oranges. Scientists also call it the “North Atlantic Warming Hole”.

Now, let’s examine the Atlantic Meridional Overturning Circulation (AMOC).

A child eats traditional porridge at a rural home, as Zimbabwe is experiencing an El Nino-induced drought. Reuters

This ‘conveyor belt’ is a vast system of ocean currents that redistributes heat across the Atlantic. It sends warm, salty water northward from the tropics via currents such as the Gulf Stream. As it reaches colder regions near Greenland, it cools, becomes denser and sinks. That cold water then flows southward at depth, eventually rising again to complete a loop that can take hundreds of years. This ‘conveyor belt’ is extremely important to climate patterns across continents.

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As per Hindustan Times, the system moves an enormous volume of water, around 18–20 sverdrups, or tens of millions of cubic metres per second.

But why does this matter? Because scientists have long wondered whether this cold blob occurs due to heat loss from the ocean surface caused by changes to winds and clouds. They also think it could be the result of the AMOC getting weaker.

This is important because the cold blob is located exactly where the AMOC delivers much of its heat. Now, more evidence is emerging linking an AMOC slowdown to the cold blob.

What the data show

CNN cited a 2026 study showing that the cooling isn’t just at the surface. In fact, it goes deep into the ocean, something that cannot be attributed to atmospheric factors alone. Some experts point to a shift in the ocean’s balance of heat and salinity. As global temperatures rise, Greenland’s ice sheet is melting at an accelerating pace, releasing large volumes of freshwater into the North Atlantic.

Freshwater is less dense than salty seawater. That makes it harder for surface water to sink, an essential step in driving the AMOC. If the sinking slows, the entire conveyor belt weakens. When that happens, less warm water reaches the North Atlantic. The result is a cooling patch in an otherwise warming ocean.

Climate scientist Stefan Rahmstorf told CNN that everything points towards the AMOC. “It is changing ocean heat transport”, which is causing the cooling of the cold blob, Rahmstorf, a study author and a physics and oceans professor at Potsdam University in Germany, said.

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Rahmstorf and colleagues published a study in Geophysical Research Letters this year. The study, which analysed temperature data, said that the cold blob was likely due to a reduction in the transport of heat in the waters because surface heat loss had declined over the years.

“To explain a cooling trend in the cold blob region by surface heat loss while the AMOC is steady, this heat loss would need to increase to outcompete the AMOC's heat supply. The opposite is seen in the ERA5 data (a global weather dataset): surface heat loss has in fact decreased (since 1993 significantly, since 1955 slightly) over the cold blob. The latter is to be expected when the AMOC supplies less heat to the region and thus less is released to the atmosphere,” the study read.

Rahmstorf isn’t alone. Multiple studies over the past decade have pointed in this direction. As per Hindustan Times, researchers at the University of California, Riverside (UCR) examined 20 years of AMOC observations and a century of oceanic temperature and salinity data, as well as 94 different climate models. They all agreed the AMOC was causing the cold blob.

The study, entitled 'Weakened Atlantic Meridional Overturning Circulation Causes the Historical North Atlantic Warming Hole', was published in the Communications Earth & Environment journal in May 2025. “If you look at the observations and compare them with all the simulations, only the weakened-AMOC scenario reproduces the cooling in this one region. It's a very robust correlation,” co-author Kai-Yuan Li was quoted as saying.

However, others are a little more circumspect.

As Jonathan Baker, a senior climate scientist at the UK Met Office, told CNN, “I would view this study as adding evidence for an AMOC contribution to the cold blob, rather than definitively settling the question.”

Others agree. “I don’t think (this study) will be the final word on the issue,” David Thornalley, a professor of ocean and climate science at University College London, added. He said the data “are best viewed as good approximations rather than perfect representations of reality.”

Why some scientists are worried

Because the slowdown in the AMOC could have dire consequences for humanity.

Hindustan Times cited research from the Potsdam Institute for Climate Impact Research (PIK) as saying that an AMOC shutdown could result in “summer drying and severe winter extremes in northwestern Europe” alongside “shifts in tropical rainfall belts”.

Scientists said annual temperatures in Germany's Bremen could drop by up to 10°C under an AMOC collapse. Meanwhile, the US could see reduced rainfall and monsoon systems in South Asia, including India, could be disrupted.

CNN reporting called an AMOC shutdown a recipe for global catastrophe. It said this could result in accelerated sea level rise on the US East Coast, Europe experiencing a winter deep freeze, and extended droughts in Africa.

As per Hindustan Times, this could make El Niño even stronger, which in turn could hurt the monsoon and millions of farmers’ livelihoods and the India's food security.

FAQs

1. What is the ‘cold blob’?

The cold blob is a region of unusually cold water in the North Atlantic that has cooled over the past century, even as the rest of the world’s oceans have warmed.

2. What is causing the cold blob?

Scientists believe it is linked to a weakening Atlantic Meridional Overturning Circulation (AMOC), caused in part by freshwater from melting Greenland ice disrupting ocean circulation.

3. Why is the cold blob a concern?

It may signal a slowdown in a key ocean current system that regulates global climate, potentially affecting weather patterns, sea levels and monsoons worldwide.

With inputs from agencies