There’s an interesting new paper in tomorrow’s Science by Rickaby and Halloran that supports the idea that warm conditions during the Pliocene were linked to a cool equatorial Pacific – a La Niña-like state:

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 Ni?a?like state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.

This is relevant because of the connection between La Niña drought in the southwestern U.S.

This is an idea I first ran across last year in a paper by Mike Mann and some other folks. It also fits quite nicely with a paper last year by Ed Cook and some other dendrochronologists linking warmer temperatures during the Medieval with widespread drought in what is now the western United States.

I don’t know a lot about this, but apparently there have been folks who have argued in the past that a warming greenhouse climate could tilt toward El Niño-like conditions. This is the latest line of evidence to contradict that assertion.