No ‘permanent El Niño,’ scientists say — and the tropics may get even hotter

Eric Gershon in the Yale News: New research by Yale University scientists challenges a long-standing paradigm for temperature variability in the Pacific Ocean, casting doubt on the existence of a past period of “permanent” El Niño-like conditions and suggesting that the tropics could grow markedly hotter.

“There’s good news and bad news about future global warming,” said Mark Pagani, professor of geology and geophysics at Yale and an author of the research, published April 4 in the journal Science. “The good news is that global warming does not drive the Pacific Ocean into a permanent El Niño-like condition with all the other regional climate impacts that come with that. The bad news is that the tropics will warm as we continue to add greenhouse gases to the atmosphere — and the recent past was probably much warmer than generally assumed.”

Modern El Niño conditions are characterized by unusually warm surface water in the eastern equatorial Pacific, and a very low overall equatorial Pacific temperature gradient. The quasi-periodic phenomenon’s effects on global weather patterns can be dramatic, including extreme rainfall in some places (Texas, for example) and drought elsewhere (Indonesia and Australia).

A conventional view holds that sea surface temperatures in the warmest part of the equatorial Pacific — the vast western “warm pool” — remained relatively constant for millions of years. Given that ocean temperatures elsewhere rose during this time, the warm pool’s stable temperature implied a tropical ocean “thermostat” or temperature control mechanism, Pagani said.

But in a new reconstruction of ancient Pacific sea surface temperatures covering 12 million years, Pagani and Yale doctoral candidate Yi Ge Zhang found that Pacific warm pool temperatures were notably higher 12 million years ago than previously thought — as much as 4°C warmer. Their results indicate that all parts of the Pacific warmed during past periods of global warming, suggesting greater variability of ancient ocean temperatures and the absence of any tropical temperature control mechanism or  “permanent El Niño-like” conditions....

Ruins at Orongo on Easter Island, shot by TravelingOtter, Wikimedia Commons via Flickr, under the Creative Commons Attribution 2.0 Generic license