SCIENCE

New study casts doubt on climate link to El Niño

A new study is challenging conventional predictions of El Niño weather patterns.

The study, published Dec. 14 in Nature Geoscience, finds that the El Niño pattern -- a warming in the equatorial Pacific Ocean associated with wet weather on the West Coast -- may be less influenced by large-scale climate trends than currently assumed.

The study challenges nine climate models in use today, which find an association between strong seasonal shifts -- exceptionally hot summers and cold winters -- and the formation of weak El Niños.

The study used existing records of up to 10,000-year-old coral and shell fossils from the Pacific Ocean to calculate the prevalence of various oxygen isotopes over time, which the researchers used as a proxy for equatorial sea surface temperatures. They found no link between strong differences in seasons and El Niño formation.

"El Niño is basically the weakening of the seasonal cycle," said lead author Julien Emile-Geay, an assistant professor of earth sciences at the University of Southern California. "We don't tend to find that in the coral records."

"Six thousand years ago, there was a pretty big difference in the angle between the sun and the Earth," Emile-Geay said, which led researchers to assume it caused a shift in El Niño patterns. "That's not really what we find. We find the time we see the greatest change in El Niño, 3,000 to 5,000 years ago, there's nothing very remarkable going on with changes in orbital configuration."

The relevance for predictions of human-caused climate change is that the models are also used to forecast future El Niño trends under warming scenarios. If they don't have their assumptions right, the predictions could be off, Emile-Geay said. "Certain aspects of the past they don't do well," he said. "It points to some fundamental deficiencies in the models."

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