The ocean plays a central role in the climate of the planet because:

	it has a huge capacity to store heat, water and carbon-dioxide
	global-scale ocean currents transport these properties over large distances
	the ocean exchanges these and other properties with the atmosphere.

Ocean currents transport warm water polewards near the surface and return cooler, denser water equator-ward in the interior, in the wind-driven and thermohaline circulations, redistributing heat and fresh water around the globe and exchanging it with the atmosphere. In the present climate the ocean transports an amount of heat polewards that is roughly equivalent to that carried by the atmosphere.