Ocean currents equalize global temperatures by moving warm water from the equator to the polar regions and returning cold water. The majority of the sun's heat is absorbed by the oceans around the equator. If ocean currents did not distribute this heat, global temperature fluctuations would be far more extreme.
Heated water molecules exchange freely with the air through evaporation. When ocean water evaporates, it increases the temperature and humidity of the surrounding air. Ocean currents work similar to a conveyor belt, distributing warm water, air and precipitation to counteract the uneven heating of the planet. Without this regulation of the global climate, regional temperatures would be so extreme that much of Earth would be uninhabitable.
Ocean currents run in a clockwise direction in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. The size, shape, speed and direction of the currents is dictated by several environmental forces and geographic characteristics. Wind, tides, the sun, water density differences and Earth's rotation affect much of a current's movements. The topography of ocean basins, and the features of nearby land masses, help guide them.
The global current infrastructure interacts not just to move water horizontally, but also vertically. This process completely circulates the world's oceans every 1,000 years.