In the Atlantic Ocean, south of Greenland and Iceland, a large body of water is doing something very unusual. While the rest of the ocean is warming, this area is cooling. A new study says it has found the answer to this mystery - and it's a worrying sign that the world is heading towards one of the most alarming climate tipping points.
This area of the ocean - called the "cold spot" - has cooled by almost 1 degree Celsius since 1900, CNN wrote.
Scientists have long debated whether this anomaly is caused by heat loss from the ocean surface due to changes in winds and clouds, or whether it is a signal of a weakening of a critical system of ocean currents that transports heat from the tropics to the north, known as the AMOC. The new research concludes that the cause is the latter, and the discovery points to a troubling future.
This system of heat-transporting ocean currents - or AMOC - functions like a giant conveyor belt in the ocean, pulling warm water from the tropics towards the Northern Hemisphere, where it cools, sinks and flows south again.
Many studies suggest that this system is weakening, as global warming caused by human activity is melting ice and bringing large amounts of freshwater into the ocean, disrupting the delicate balance of heat and salinity that keeps the AMOC functioning.
Some scientists warn that the AMOC is approaching a critical tipping point, which would mean that a future collapse would become inevitable.
A complete shutdown of the AMOC would be a global catastrophe, causing accelerated sea level rise along the US east coast, very harsh and cold winters in Europe, and changes in Africa's rainfall systems, bringing long and severe droughts.
To better understand what's happening in this part of the Atlantic, the study's authors combined real-world data on ocean heat, collected by instruments and satellites, with computer climate models.
They found that the cooling at the "cold spot" was not only happening at the surface, but also deep in the ocean, where atmospheric conditions such as winds and clouds have much less of an impact.
All indicators point to the influence of the AMOC, according to the study.
"It's changing the heat transport in the ocean," said Stefan Rahmstorf, one of the study's authors.
"This is causing the cold spot to cool."
He added that there is also plenty of other evidence, independent of the "cold spot" phenomenon, that shows that the AMOC is weakening, and some studies suggest that it is now at its weakest in about 1,000 years.