Ocean Currents Are Changing but the Threat Is Unknown Shallow and deep ocean currents are connected and move like a gigantic conveyor belt, transferring CO2 and warm and cool water between the surface and the depths and between the tropics and the poles (Figure 7-5, p. 143). Scientists are concerned that melting of landbased glaciers (especially in Greenland) and increased rain in the North Atlantic, both due to global warming, could add enough freshwater to the ocean in the arctic area to slow or disrupt this conveyor belt. Reaching this irreversible tipping point would drastically alter the climates of northern Europe, northeastern North America, and probably Japan (Concept 19-2). Most climate scientists do not see this as a threat in the near future, based on projected temperature increases (Figure 19-B). But we still have much to learn about this pattern of ocean circulation, and ice in land-based glaciers is melting faster than most scientists expected.