Chapter 4 · Try it yourself

The El Niño Switch

Normally the trade winds blow west across the Pacific and pile warm water up against Indonesia, leaving cool, food-rich water around the Galápagos. Every few years the winds falter, and the whole warm pile sloshes back east. Fishermen in Peru named it El Niño. Slide the winds and watch.

Warm pool (29 °C +)WarmCoolCold deep water

The dashed line is the thermocline: warm water above, cold nutrient-rich water below. The sea-surface slope is hugely exaggerated: normally the Pacific is only about half a meter higher on the Indonesian side.

The Pacific is in
Normal conditions

  • 24 °Csea temperature at the Galápagos
  • 50 mthermocline depth near the Galápagos

Food for penguins and marine iguanas

Across the Pacific along the equator

Cross-section of the Pacific. Trade winds Cold, nutrient-rich water ← West 180° (date line) Galápagos SOUTH AMERICA INDONESIA Warm pool

Simplified model: one slice along the equator, depths to about 250 m, with temperatures and depths set to typical values for each state rather than any real year. Real El Niños build over months and each one is different.