Even quiet volcanoes release a lot of sulphur into the air

This finding will help scientists improve global climate models.

These sulphurous plumes  in Laugavegur, Iceland, are not recorded by satellite observations but by ice core analysis, which shows that the plumes have a much larger effect on the level of aerosols in the atmosphere than previously believed. 

New research led by the University of Washington (UW) shows that even in their quiet phases volcanoes release at least three times as much sulphur into the Arctic atmosphere than estimated by current climate models. The study’s findings, which were published in a recent issue of Geophysical Research Letters, have implications for scientists’ understanding of the atmosphere and its relationship with climate and air quality.

Layers of a central Greenland ice core were analysed to calculate levels of sulphate aerosols between the years 1200 and 1850. The authors had wanted to look at the sulphur emitted by marine phytoplankton, which were believed to be the biggest source of atmospheric sulphate in pre-industrial times. The team focussed on this time period as it avoids major volcanic eruptions and makes it easier to distinguish between volcanic and marine sources. “We don’t know what the natural, pristine atmosphere looks like, in terms of aerosols,” said senior author Becky Alexander, a UW professor. “Knowing that is a first step to better understanding how humans have influenced our atmosphere.”

“We were planning to calculate the amount of sulphate coming out of volcanoes, subtract it, and move on to study marine phytoplankton,” said Ursula Jongebloed of UW, the first author of the paper. “But when I first calculated the amount from volcanoes, we decided that we needed to stop and address that.”

“We found that on longer timescales the amount of sulphate aerosols released during passive degassing is much higher than during eruptions,” she said. “Passive degassing releases at least 10 times more sulphur into the atmosphere, on decadal timescales, than eruptions, and it could be as much as 30 times more.”

“Our results suggest that volcanoes, even in the absence of major eruptions, are twice as important as marine phytoplankton,” Jongebloed said.

Aerosol particles, whether from volcanoes, automobiles, factory chimneys, or firewood burning, block some solar energy. If the natural levels of aerosols are higher, that means the rise and fall of emissions caused by humans have had less of an effect on temperature than previously believed. “When we increase volcanic emissions, which increase the baseline of sulphate aerosols, we decrease the effect that the human-made aerosols have on the climate by up to a factor of two,” Jongebloed said. That can improve global climate models.