1. El Niño and La Niña Two climate mysteries What causes them? Why do they occur?

5. Under normal conditions, easterly trade winds move water and air warmed by the sun towards the west This also creates an upwelling of nutrient-rich cold water along the coasts of Peru and Ecuador

7. Under El Niño conditions, warm, nutrient-poor water slumps towards the east because of weakening winds The nutrient-rich cold water does not get pulled up as much

8. El Niño’s warm current of nutrient-poor tropical water replaces the cold, nutrient-rich surface water where Peru’s fishing industry usually is vibrant

10. But it doesn’t stop there! The warmer ocean then affects the winds, and makes the winds weaker. So if the winds get weaker, then the ocean gets warmer, which makes the winds get weaker. This is called positive feedback, and it’s what makes El Niño grow.

11. But it doesn’t stop there! What stops positive feedback are Rossby waves When El Niño gets going in the middle or eastern part of the Pacific, it creates Rossby waves that drift slowly towards southeast Asia. After several months of traveling, the finally get near the coast and reflect back. The changes in interior ocean temperature that these waves carry with it “cancel out” the original temperature changes that made the El Niño in the first place

12. The Effects of El Niño are Worldwide

19. Under La Niña conditions, unusually cold water pushes up in the east Pacific Often follows El Niño

21. What the heck causes El Niño and La Niña?