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Oceans cover approximately 70 percent of the earth and holds 97 percent of its water, making the ocean a key factor in the storage and transfer of heat energy across the globe. The movement of heat through ocean currents works similarly to the movement of heat through air - it affects local weather conditions and temperature extremes, climate patterns, cycling of gases, and delivery of nutrients to marine ecosystems.

Ocean currents flow for great distances, and together, create the global conveyor belt which determines the climate of many of the earth’s regions. This image shows the many currents -- both warm and cold -- and the many paths taken around the ocean. These currents influence the temperature of the regions through which they travel. For example, warm currents traveling along more temperate coasts increase the temperature of the area by warming the sea breezes that blow over them. Take the Gulf Stream, for example. It makes northwest Europe much more temperate than any other region at the same latitude.

Knowledge of surface ocean currents is essential to the economy. Costs of shipping goods can be reduced since traveling with them reduces fuel consumption. In the wind powered sailing era, knowledge of wind patterns and ocean currents was even more essential.

Ocean currents are important in the study of marine debris, and vice versa. These currents also affect temperatures throughout the world. For example, the ocean current that brings warm water up the north Atlantic to northwest Europe also cumulatively and slowly blocks ice from forming along the seashores, which would also block ships from entering and exiting inland waterways and seaports, hence ocean currents play a decisive role in influencing the climates of regions through which they flow. Cold ocean water currents flowing from polar and sub-polar regions bring in a lot of plankton that are crucial to the continued survival of several key sea creature species in marine ecosystems. Since plankton are the food of fish, abundant fish populations often live where these currents prevail. Ocean currents can also be used for marine power generation.