In El Niño years, huge masses of warm water – equivalent to about half of the volume of the Mediterranean Sea – slosh east across the Pacific Ocean towards South America. That mass of warm water puts a lid on the normal currents of cold, deep water that typically rise to the surface along the equator and off the coast of Chile and Peru.
"An El Niño basically stops the normal upwelling," Uz said. "There’s a lot of starvation that happens to the marine food web." These small plants, called phytoplankton, are fish food – without them, fish populations drop, and the fishing industries that many coastal regions depend on can collapse.