large-scale weather phenomenon occurs every few years when prevailing winds in the tropical Pacific Ocean weaken and change direction
o Above-average warming of Pacific waters affects populations of marine species by changing the distribution of plant nutrients, hurting fishing industry
o Low nutrients, low dissolved oxygen (in South America, but in Australia during La Niña)
o Severe flooding, storms, drought, mudslides, $ damage, human health hazards (dehydration, diarrhea, zoonotic diseases [lyme, Hanta])