El Nino and La Nina The tropical Pacific Ocean (1)______________ a warming and cooling cycle. This cycle is a completely natural event and usually (2)___________ between three to seven years. When the waters become (3)______________, it is called El Nino, and when they become cooler it is called La Nina. During the cycle, the (4)___________ of the ocean can change by around 3oC between the warmest and coolest times. (5)_____________ off the South American coast have known about this (6)____________ event for hundreds of years. When it (7)____________, they see a huge fall in the numbers of fish caught. But scientists are only just beginning to (8)____________ how the event affects Earth’s weather and climate.