Volcanoes especially emit a lot of sulfur when they erupt, or so it was always thought. But it now appears that dormant volcanoes also release a surprising amount of sulfur particles into the air.
Research in Greenland ice shows that volcanoes at rest emit three times more sulfur than estimated by current climate models. “We discovered that over a longer period of time, the amount of sulfur particles released during passive degassing is much greater than during eruptions,” says lead researcher Ursula Jongebloed of the University of Washington. “Passive degassing releases at least 10 times more sulfur into the atmosphere over a 10-year period than eruptions, and it could be as much as 30 times more.” These plumes of gas leaking from dormant volcanoes are not picked up by satellite images. That may explain why the amount has been underestimated so far.
Pure atmosphere
The international research team analyzed ice sheets from an ice core they had drilled out in Central Greenland to calculate the number of sulfur particles between the years 1200 and 1850. The researchers wanted to look at the amount of sulfur that phytoplankton emitted during that period. It was previously thought to be the largest source of sulfur in the atmosphere in the pre-industrial era. “We don’t know what the natural, pure atmosphere looked like, in terms of aerosols,” says researcher Becky Alexander of the background to the study. “We need to know that first to better understand how humans have affected the atmosphere.”
Fytoplankton
The research team deliberately avoided major volcanic eruptions and focused on the pre-industrial period when it is easier to distinguish between volcanic and marine sources of sulfur emissions. “We planned to calculate the amount of sulfur coming from volcanoes and subtract it from the total sulfur emissions and then continue with the study of phytoplankton,” explains Jongebloed. “But when we found out how much sulfur was coming out of the volcanoes, we decided to investigate that first.”
The ice core at the center of the Greenland Ice Sheet contains emissions from sources from much of North America, Europe and surrounding oceans. Although this research only applies to this area, the researchers expect that the results will also apply to the rest of the world. “Our findings indicate that volcanoes, even when they are not erupting, emit twice as much sulfur as phytoplankton,” says Jongebloed.
Three times as much as expected
The discovery that dormant volcanoes leak up to three times more sulfur than previously thought has an impact on current climate models. Particles in the air, whether they come from volcanoes, cars or factories, block the sun’s rays. If the natural level of aerosols is higher, this means that human emissions have less influence on the temperature than previously thought.
But the effect of sulfur in the atmosphere is complex. “There is a sort of diminishing additional yield with sulfur particles: the more you have, the less effect extra sulfur has,” explains Jongebloed. “As volcanoes’ emissions increase, the effect human-made aerosols have on the climate decreases by a factor of two.” In other words, if natural sulfur emissions are greater, we may have overestimated the cooling effect of sulfur pollution from industry. This may explain why the polar region is warming faster than previously calculated: the initial level of the amount of aerosols in the air is higher than previously thought.
Neither good nor bad news
But more research is needed to determine the effects on global warming. “We think the missing emissions from volcanoes are from hydrogen sulfide,” Alexander said, referring to the gas smelling like rotten eggs. “The best way to better estimate these emissions from volcanoes is to look closely at hydrogen sulfide emissions.”
The researcher therefore regards the discovery as ‘neither good nor bad news for the climate’. “But if we want to understand how much the earth will warm in the future, it helps to have a better estimate of the aerosols in the air.” As a result, the climate models can be improved.
