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Cool La Niña during the warmth of the Pliocene?

Rickaby RE, Halloran P

Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK.

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.

Published 25 March 2005 in Science, 307(5717): 1948-52.
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