Cool La Niña During the Warmth of the Pliocene?

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Science  25 Mar 2005:
Vol. 307, Issue 5717, pp. 1948-1952
DOI: 10.1126/science.1104666

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The role of El Niño–Southern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Niña–like state, rather than the proposed persistent warm El Niño–like conditions. Our Pliocene paleothermometer supports the idea of a dynamic “ocean thermostat” in which heating of the tropical Pacific leads to a cooling of the east equatorial Pacific and a La Niña–like state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.

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