Ice cores show even dormant volcanoes leak abundant sulphur into the atmosphere according to new research from the University of Washington

Volcanoes draw plenty of attention when they erupt, but new research shows that volcanoes leak a surprisingly high amount of their atmosphere- and climate-changing gases in their quiet phases.

A Greenland ice core shows that volcanoes quietly release at least three times as much sulphur into the Arctic atmosphere than estimated by current climate models.

The study, led by the University of Washington has implications for better understanding Earth’s atmosphere and its relationship with climate and air quality.

First author Ursula Jongebloed, a UW doctoral student in atmospheric sciences, said: “We found that on longer timescales the amount of sulphate aerosols released during passive degassing is much higher than during eruptions.

“Passive degassing releases at least ten times more sulphur into the atmosphere, on decadal timescales, than eruptions, and it could be as much as 30 times more.”

See also: Volcanoes could have caused whale extinctions

atmospheric sulphate

The international team analysed layers of an ice core from central Greenland to calculate levels of sulphate aerosols between the years 1200 and 1850.

The authors wanted to look at the sulphur emitted by marine phytoplankton, which were previously believed to be the biggest source of atmospheric sulphate in pre-industrial times.

Senior author Becky Alexander, a UW professor of atmospheric sciences, said: “We don’t know what the natural, pristine atmosphere looks like, in terms of aerosols.

“Knowing that is a first step to better understanding how humans have influenced our atmosphere.”

The team deliberately avoided any major volcanic eruptions and focused on the pre-industrial period, when it’s easier to distinguish the volcanic and marine sources.

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

The location of the ice core at the centre of the Greenland Ice Sheet records emissions from sources over a wide swathe of North America, Europe and surrounding oceans. While this result applies only to geologic sources within that area, including volcanoes in Iceland, the authors expect it would apply elsewhere.

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

Mount Hood

The discovery that non-erupting volcanoes leak sulphur at up to three times the rate previously believed is important for efforts to model past, present and future climate.

Aerosol particles, whether from volcanoes, vehicle tailpipes or factory chimneys, block some solar energy. If the natural levels of aerosols are higher, that means the rise and fall of human emissions – peaking with the acid rain of the 1970s and then dropping with the Clean Air Act and increasingly strict air quality standards – have had less of an effect on temperature than previously believed.

Jongebloed added: “There’s sort of a ‘diminishing returns’ effect of sulphate aerosols; the more that you have, the less the effect of additional sulphates.

“When we increase volcanic emissions, which increases 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.”

That means Arctic warming in recent decades is showing more the full effects of rising heat-trapping greenhouse gases, which is by far the main control on Earth’s average temperature.

Jongebloed said of the result: “It’s not good news or bad news for climate. But if we want to understand how much the climate will warm in the future, it helps to have better estimates for aerosols.”

Better estimates for aerosols can improve global climate models.

Alexander stated: “We think that the missing emissions from volcanoes are from hydrogen sulphide.

“We think that the best ways to improve these estimates of volcanic emissions is to really think about the hydrogen sulphide emissions.”

The research is published in Geophysical Research Letters.

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

Bottom image: This plume escaping from a lake near the summit of Oregon’s Mount Hood, seen in May 2021, is not captured by satellite observations. Ice core analysis shows that such plumes have a much larger effect on the level of aerosols in the atmosphere than previously believed.

Both images: Credit: Ursula Jongebloed/ University of Washington.