In the Atlantic Ocean, a giant ‘conveyor belt’ carries warm waters from the tropics into the North Atlantic, where they cool and sink and then return southwards in the deep ocean. This circulation pattern is an important player in the global climate, regulating weather patterns in the Arctic, Europe, and around the world. Evidence increasingly suggests that this system is slowing down, and some scientists fear it could have major effects, such as causing temperatures to dive in Europe and warming the waters off the East coast of the United States, potentially harming fisheries and exacerbating hurricanes. (For an over-exaggeration of the potential effects, see the 2004 movie The Day After Tomorrow.)