Warm ocean currents transport warm water from the tropics towards the poles and cold,deep currents transport cold water from the poles towards the tropics.Thus they determine the climate and weather of continents.For example,the Gulf stream(warm current) makes the north-west Europe much more moderate than any other region in the same latitude.
the conveyor belt, water travels to the polls cools, sinks to the bottom, travels towards the equator, warms up rises and repeats.
fresh water changes the density and the water begins to “sink” at a slightly different temp. this is why global warming will cause the earth to cool.
the conveyor will shut down causing the the extreme hemispheres to be cooler