Since
the 1800s, Peruvian fisherman noticed that their
harvest completely failed every few years. This
periodic event was associated with unusually warm
waters off the coast of Peru.
These warm waters
resulted from a shutdown of the upwelling circulation
normally found along the equator. Since
upwelling supplies nutrients to the surface waters,
this resulted in mass starvation of plant and
animal life in the eastern equatorial Pacific. Since
the periodic warming almost always occurred around
December, the fisherman named it El Ni–o, in
reference to the Christ child.