El Nino events can be triggered by major volcanic eruptions in the tropics

New research suggests the eruption of large volcanoes in the tropics can trigger an El Niño event, the Pacific Ocean warming pattern that impacts global climate.

The El Niño Southern Oscillation describes a periodic variation in winds and sea surface temperatures. The irregular variability features two main patterns: a warming pattern, El Niño, and a cooling pattern, La Niña. One of the two pattens forms roughly every three to seven years. The pattern typically forms toward the end of the calendar year and lasts through the winter months.

Researchers at the University of Rutgers looked at the ENSO patterns in the wake of several tropical volcanic eruptions, including the eruptions of Guatemala's Santa María in 1902, Indonesia's Mount Agung in 1963 and Mexico's El Chichón and Pinatubo in 1982 and 1991.

Scientists looked most closely at Pinatubo, for which researchers had the most detailed atmospheric data. Their analysis -- detailed this week in the journal Nature Communications -- showed the 20 million tons of sulfur dioxide emitted by Mount Pinatubo triggered a cascading series of climate interactions that encouraged the formation of an El Niño in the Pacific.

Large clouds of sulfur dioxide in the stratosphere work to reflect solar energy, and encouraging cooling. In the case of Pinatubo, the uptick in SO2 caused in cooling tropical Africa, which depressed the West African monsoon and drove equatorial westerlies across the western Pacific. The wind pattern anomalies encouraged air-sea interactions that favored an El Niño-like response.

The new model created by researchers at Rutgers agreed with historical patterns, which showed El Niño patterns were more likely to form the year after a major tropical eruption.

"We can't predict volcanic eruptions, but when the next one happens, we'll be able to do a much better job predicting the next several seasons, and before Pinatubo we really had no idea," Alan Robock, a professor of environmental sciences at Rutgers, said in a news release. "All we need is one number -- how much sulfur dioxide goes into the stratosphere - and you can measure it with satellites the day after an eruption."

The new model also showed in influx of SO2 from tropical volcanoes can prematurely end a La Niña event, as well as trigger warming during a neutral ENSO pattern. Scientists say their model could be used to more accurately predict future precipitation totals.

"If you're a farmer and you're in a part of the world where El Niño or the lack of one determines how much rainfall you will get, you could make plans ahead of time for what crops to grow, based on the prediction for precipitation," Robock said.

Previous studies suggest El Niño events are associated with a variety of weather patterns across the globe. The warming pattern tends to suppress hurricane activity in the Atlantic, promote milder winter temperatures across Canada and encourage cold season coastal storms along the Eastern Seaboard -- among other impacts.

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