Ocean Currents: The Hidden Engine

The sun creates climate zones, but oceans and winds modify them dramatically. Northwestern Europe is far milder than its latitude suggests: London (51 degrees N) has gentle winters while Labrador, Canada (also 51 degrees N) is buried in ice. The main reason is that prevailing south-westerly winds blow off the relatively warm North Atlantic and carry that mild maritime air over Europe, whereas north-westerly winds drag frigid continental air across eastern North America. The warm ocean (including the Gulf Stream) helps keep that incoming air mild, but it is the wind-driven atmospheric heat transport, not the current alone, that does most of the work.

The cold Humboldt Current running along South America's west coast helps create the Atacama Desert — the driest non-polar desert and one of the driest places on Earth — by cooling the air so much that it cannot hold moisture.