Global ocean thermohaline circulation. Illustration of the large slow global currents driven by thermohaline circulation in the world's oceans. These currents are driven by differences in temperature and salinity. Warm water (red) on the surface of the Indian and Pacific oceans flows westwards and northwards through the Atlantic, with evaporation making the water saltier along the way. At colder northern latitudes, the water becomes dense enough to sink to the sea floor where it travels south (blue), re-emerging in the western parts of the Indian and Pacific oceans. Disruption of this thermohaline circulation could cause severe climate change.