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Tropical volcanoes trigger El Niños, says study

A new study shows how large volcanic eruptions cool tropical Africa, spawning El Niño events.

Mount Pinatubo eruption 1991. Image via Volquake.weebly.

Explosive volcanic eruptions in the tropics can lead to El Niño events, the warming periods in the Pacific Ocean that have dramatic impacts on global climate. That’s according to a new study published online on October 3, 2017 in Nature Communications.

The study used climate model simulations to show that El Niño tends to peak during the year after large volcanic eruptions, such as the one at Mount Pinatubo in the Philippines in 1991.

An El Niño, which is a reoccurring natural phenomenon, happens when sea surface temperatures in the equatorial Pacific Ocean warm up. The increased ocean surface temperatures influence air and moisture movement around the globe, causing worldwide impacts on the climate. For example, strong El Niño events can lead to elevated sea levels and potentially damaging cold-season nor’easters along the U.S. East Coast.

The researchers say that enormous volcanic eruptions trigger El Niño events by pumping millions of tons of sulfur dioxide into the stratosphere, which then forms a sulfuric acid cloud, reflecting solar radiation and reducing the average global surface temperature,

Mount Pinatubo in the Philippines erupting on June 12, 1991. A much larger eruption occurred three days later. Image via US Geological Survey/Rutgers.

According to the study, sea surface temperature data since 1882 document large El Niño-like patterns following four out of five big eruptions: Santa María (Guatemala) in October 1902, Mount Agung (Indonesia) in March 1963, El Chichón (Mexico) in April 1982 and Pinatubo in June 1991.

Cooling in tropical Africa after volcanic eruptions weakens the West African monsoon, and drives westerly wind anomalies near the equator over the western Pacific, the study says. The anomalies are amplified by air-sea interactions in the Pacific, favoring an El Niño-like response. Climate model simulations show that Pinatubo-like eruptions tend to shorten La Niñas (periods of below-average sea surface temperatures across the east-central Equatorial Pacific that tend to have opposite impacts of El Niño), lengthen El Niños and lead to unusual warming during neutral periods, the study says.

The study focused on the Mount Pinatubo eruption because it’s the largest and best-documented tropical one in the modern technology period. It ejected about 20 million tons of sulfur dioxide.

Damage from volcanic ash at Clark Air Force Base in the Philippines after the June 15, 1991, eruption of Mount Pinatubo. Image via Richard Hoblitt/US Geological Survey/Rutgers.

Alan Robock, a professor in the Department of Environmental Sciences at Rutgers University-New Brunswick, co-authored the study. Robock said in a statement:

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. 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.

Bottom line: A new study says that large volcanic eruptions cool tropical Africa and spawn El Niños events.

Read more from Rutgers University

Eleanor Imster

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