The collapse of a critical ocean current system—an event that would upend Earth’s climate and wreak havoc on the Americas, Europe, and Africa—has been the subject of heated scientific debate for more than a decade. Experts have differing opinions on how imminent this disaster really is, but a new study may have just confirmed their worst fears.

The findings, published Wednesday in the journal Science Advances, suggest that the Atlantic Meridional Overturning Circulation (AMOC) is on track for a 43% to 58% slowdown by 2100—a substantial weakening that is 60% stronger than than the average estimate of all climate models.

This is “seriously bad news,” Stefan Rahmstorf, an oceanographer at the Potsdam Institute for Climate Impact Research in Germany, wrote on social media. He was not involved in the research, but he has studied the AMOC system for more than 35 years.

“I am now increasingly worried that we may well pass that AMOC shutdown tipping point, where it becomes inevitable, in the middle of this century, which is quite close,” Rahmstorf told The Guardian.

A catastrophic collapse

The AMOC is a critical part of an even larger system of currents that transport water throughout the world’s oceans. Driven by changes in salinity and ocean temperature, it circulates water from north to south and back again within the Atlantic Ocean. This circulation redistributes heat from the tropics to the Arctic, and therefore plays an essential role in regulating Earth’s climate.