The thermohaline circulation (from the Greek thermos "heat" and halos "salt") is the global system of deep ocean currents that redistributes heat and nutrients across the entire planet, acting as an oceanic conveyor belt. The primary engine is the sinking of dense (cold and salty) surface water in the North Atlantic, near Greenland and Iceland, where water cooled by Arctic air and concentrated in salt by evaporation sinks to the ocean floor and flows southward. This deep water travels along the Atlantic seabed, circles Antarctica, enters the Indian and Pacific Oceans, and gradually upwells over centuries. A complete cycle takes approximately 1,000 years. The Atlantic component is called the AMOC (Atlantic Meridional Overturning Circulation) and is responsible for western Europe having a significantly milder climate than other regions at the same latitude—it transports the equivalent of one million nuclear power plants in thermal energy northward. Climate change threatens this system: Greenland ice melt and increased precipitation at high latitudes dilute North Atlantic salinity, reducing water density and weakening the sinking process. Recent studies suggest the AMOC has weakened by 15–20% since the mid-20th century. A complete collapse—possible but unlikely this century—would have drastic consequences: abrupt European cooling, disruption of the monsoons, and sea level rise along the western Atlantic coast.