Climate models have long warned that global warming could weaken “deep-water formation”—the density-driven sinking that is the engine of the AMOC. The logic is straightforward: As Greenland’s ice sheets melt and sea ice formation declines, North Atlantic waters will freshen. Combined with warmer sea temperatures, the freshening makes surface waters more buoyant. The AMOC was thought to have shut down abruptly during past climate warmings, and a handful of researchers now argue such a tipping point could occur this century. A sputtering AMOC could trigger a sharp cooldown in northwestern Europe, rising seas along the U.S. east coast, and shifts in tropical rainfall. “It is a risk that would really have severe impacts,” says Stefan Rahmstorf, a climate scientist at Potsdam University and a prominent voice warning of the threat.

Yet for all the alarming headlines, most climate researchers think the AMOC is more resilient than these worst case scenarios make it seem. Emerging evidence suggests the AMOC may not have actually collapsed in the warm climates following ice ages. More detailed climate models suggest it could weaken but not collapse in the current surge of warming. And studies of the AMOC’s present behavior do not yet show any clear signs of trouble. They’re also exposing new facets of the circulation that could buffer any eventual weakening.

“The paradigm has been, if we warm and freshen these areas, we’ll get less dense water and AMOC will slow down,” says Susan Lozier, an oceanographer at the Georgia Institute of Technology. “That paradigm isn’t holding up.”