The Humboldt Current is an ocean current off the western coast of South America that flows to the north, carrying cold water from the Southern Ocean.
Because it carries water from the Southern Ocean, the Humboldt is a cold current. The water along the western shore of South America, almost up to the equator, is almost as cool as the water around London or Vancouver, British Columbia. This provides a very fertile ground for sea life, making this region very important, both biologically and economically. The cold ocean water and attendant high pressure also means that the coast of South America receives little rain, leading to the driest area in the world: the Atacama Desert.
The climactic outfall from this ocean current ripple far beyond just one desert, because the cold ocean water and high pressure air above it lead to one of the most important phenomena in the global climate: what is often called El Nino, but is sometimes called the El Nino/Southern Oscillation. When the cold water of the Humboldt current either heats up or cools down by a degree or so, the weather patterns over the Pacific change, and then ripple out to change weather patterns over the entire world.
Thus, while the Humboldt Current may seem a rather minor affair: a current that carries cold water into warmer climates, it is actually one of the most important pieces of the global climate puzzle.