The Pacific acquires El Nino
A permanently warm eastern Pacific gives way to the modern east-west temperature contrast.
- When
- —
- Duration
- 1.5 million years
- Known to
- ± 500 thousand years
- Era
- Pliocene, Cenozoic
Through the early Pliocene the eastern equatorial Pacific is anomalously warm and the east-west sea surface temperature gradient is weak — a state sometimes described as a permanent El Nino. Through the late Pliocene the cold tongue develops, the gradient steepens, and the Walker circulation strengthens into its modern form, which is what makes El Nino an oscillation rather than a permanent condition. The change alters rainfall patterns across the tropics, including over East Africa.