The circulation of the world's oceans generally mirrors the movements of the atmosphere. Surface currents driven by atmospheric winds move warm equatorial waters to the poles and cold polar waters toward the equator—setting up nearly circular patterns of movement known as gyres. Before steam-powered ships were introduced in the nineteenth century, sailors used these winds and currents to cross vast stretches of ocean. Many of the routes they took, such as those between Europe and America, were physically longer than the trade routes used today. Rather than setting out directly west from Europe, sailors moved parallel to the west coasts of Europe and North Africa until they reached the "trade winds" that carried them westward across the Atlantic to the Caribbean.

Today scientists recognize that ocean currents are more than natural highways of commerce. These massive movements of ocean water play a pivotal role in determining the climate of Earth, although their behavior is not entirely understood. And, of the myriad currents flowing through the open ocean and along the edges of continents, the Gulf Stream may have the greatest influence on climate.

This swift-moving current transports more than 100 times the outflow of all the world's rivers as it moves northeastward from Cuba to Newfoundland. Caribbean heat continues eastward (in the form of the North Atlantic Drift), greatly moderating the coastal European climate. Much of Britain, the southern parts of which lie north of the U.S.–Canadian border, experiences winters as mild as those of northern Florida, Georgia, and South Carolina, which are fifteen to twenty degrees in latitude further south!

The counterpart to the Gulf Stream in the Pacific is the Kuroshio (or Japan) Current, which moves from the Philippines northward past Taiwan and Japan. Overall, the climatic effects of the Kuroshio Current are less extensive than those of the Gulf Stream. Towering mountain ranges along the west coast of North America confine the effects of the current's waters to relatively small areas. Other, similar currents affect climate on the rest of the planet. The relatively cold California, Peru, Benguela, and Canary Currents flow around the west coasts of the Americas, Africa, and Europe, creating cool, moist surface air with frequent fog and overcast skies.

Source: MSP2. Oceans, Weather, and Climate. Retrieved from http://msteacher.org/epubs/science/science6/forecast.aspx on November 19, 2010.