At some point, melting ice in the North Atlantic—caused by increased global warming—will cause so much freshwater to be introduced that the Atlantic Meridional Overturning Circulation (AMOC) system will reach an abrupt threshold, beyond which there could be large, accelerating, and possibly irreversible changes in this circulatory system and its salinity, pushing it toward collapse. This is more than speculation; it’s happened in the past.But there’s a catch: Evidence for a modern-day implosion of the AMOC is still relatively new—only a few decades old—and the computer models themselves have sometimes been called into question.