El Niño events can raise the average global temperature by a few tenths of a degree Fahrenheit for a year or two. Likewise, La Niña events can produce a comparable cooling effect. Neither of these short-lived cyclic phenomena explain the longer-term warming observed in the last century and especially in the last 30 to 40 years.

(For an in-depth look at these Pacific Ocean patterns that have such an influence on short-term weather, see: Children of the Tropics: El Niño and La Niña.)