In the North Atlantic Ocean, south of Greenland and Iceland, a large patch of water is doing something very strange. While the rest of the ocean heats up, it’s been getting colder. A new study says it has the answer to this mystery — and it’s an ominous sign the world is hurtling toward one of the most alarming climate tipping points.The swath of ocean — dubbed the “cold blob” or “warming hole” — has cooled by nearly 1 degree Celsius (1.8 Fahrenheit) since 1900.Scientists have long debated whether this anomaly is driven by heat loss from the ocean surface due to changes to winds and clouds, or whether it’s a signal of the weakening of a critical system of ocean currents, which transports heat. The new research concludes it’s the latter, and the finding points to a worrying future.AdvertisementAdvertisementThe Atlantic Meridional Overturning Circulation, or AMOC, works like a vast ocean conveyor belt, pulling warm water from the tropics to the Northern Hemisphere, where it cools, sinks and flows back south.A raft of research suggests this system is weakening as human-driven global warming melts ice and causes a surge of freshwater into the ocean, disrupting the AMOC’s delicate balance of heat and salinity. Some scientists warn the AMOC is heading toward a tipping point, potentially as early at this century, which would mean a future collapse is locked in.An AMOC shutdown would be a global catastrophe, causing accelerated sea level rise on the US East Coast, plunging Europe into a winter deep freeze and shifting the monsoon in Africa, driving prolonged droughts.The cold blob has been interpreted by some as a fingerprint of AMOC change, because it’s the region to which the AMOC brings much of its heat.AdvertisementAdvertisementTo better unravel what’s happening in this part of the Atlantic, the study scientists combined real-world ocean heat data from instruments and satellites with climate models.They found that cooling in the cold blob was not just happening on the surface but also deep in the ocean, where atmospheric conditions like winds and clouds have a much weaker influence.All signs point to the influence of the AMOC, the study found. “It is changing ocean heat transport” which is driving the cooling of the cold blob, said Stefan Rahmstorf, a study author and a physics and oceans professor at Potsdam University, Germany.There is also plenty of other evidence the AMOC is weakening, independent of the cold blob, he added, with some studies suggesting it’s at the weakest it’s been in around 1,000 years.Visualization of ocean currents in the North Atlantic. The colors show sea surface temperature (orange and …
