Currents involve movement of ocean water masses, driven either by wind or by differences in temperature, salinity and density. The most important from a human perspective are the wind-driven surface currents that move water in the uppermost layer of the ocean.
Currents affect humans in several primary ways. Currents help shape the climate in the areas where we live, create the right conditions to support abundant ocean life in the areas where we fish, and change weather patterns through periodic events like El Nino/La Nina.
The single most important effect currents have on humans is that of altering climate. Together with air circulation, ocean currents act as conveyors for heat, carrying it from the equator to northern or southern latitudes. London is at the same latitude as icy James Bay in Canada, for example, but thanks to the circular current pattern of the North Atlantic Gyre, London enjoys a much milder climate.
Ocean currents also cause upwelling in many areas like off the coast of Peru, where surface currents taking water away from the shore cause nutrient-rich water to well up from the ocean deeps. The abundance of nutrients in these areas forms fertile ground for kelp beds and marine fisheries, which in turn furnish food for humans. Alterations in current patterns like the El Nino/La Nina cycle affect humans as well by causing changes in local weather patterns in the years when they occur.