Volcanic eruptions can trigger El Nino events

New York: Large volcanic eruptions in the tropics can lead to El Nino events, notorious warming periods in the Pacific Ocean with dramatic global impact on the climate, says a new study.

Enormous eruptions trigger El Nino events by pumping millions of tonnes of sulfur dioxide into the stratosphere, which form a sulfuric acid cloud, reflecting solar radiation and reducing the average global surface temperature, said the study published online in the journal Nature Communications.

The researchers used sophisticated climate model simulations to show that El Nino tends to peak during the year after large volcanic eruptions like the one at Mount Pinatubo in the Philippines in 1991.

"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," said Alan Robock, Professor at Rutgers University-New Brunswick in the US.

"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," Robock added.

The El Nino Southern Oscillation (ENSO) is nature's leading mode of periodic climate variability. 

It features sea surface temperature anomalies in the central and eastern Pacific. 

ENSO events (consisting of El Nino or La Nina, a cooling period) unfold every three to seven years and usually peak at the end of the calendar year, causing worldwide impact on the climate by altering atmospheric circulation, the study noted.

Sea surface temperature data since 1882 documents large El Nino-like patterns following four out of five big eruptions -- Santa Maria (Guatemala) in October 1902, Mount Agung (Indonesia) in March 1963, El Chichon (Mexico) in April 1982 and Pinatubo in June 1991.

The study focused on the Mount Pinatubo eruption because it is the largest and best-documented tropical one in the modern technology period. It ejected about 20 million tonnes of sulfur dioxide, Robock said.

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 said. 

The anomalies are amplified by air-sea interactions in the Pacific, favouring an El Nino-like response.

Climate model simulations showed that Pinatubo-like eruptions tend to shorten La Ninas, lengthen El Ninos and lead to unusual warming during neutral periods, the study said.