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Climate Models Underestimate Passive Volcanic Sulfur Emissions

When volcanoes erupt, they attract more attention. However, new research by the University of Washington reveals that during their quiet phases, volcanoes leak a surprisingly large amount of their atmosphere- and climate-changing gases.

Climate Models Underestimate Passive Volcanic Sulfur Emissions
These sulfurous 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. Image Credit: University of Washington

A Greenland ice core revealed that volcanoes discreetly release at least three times more sulfur into the Arctic atmosphere than what current climate models predict.

The research, guided by the University of Washington and published in Geophysical Research Letters on January 2nd, 2023, has repercussions for better understanding the Earth’s atmosphere and its relationship to climate and air quality.

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

Ursula Jongebloed, Study First Author and Doctoral Student, Atmospheric Sciences, University of Washington

The international group examined layers of an ice core from central Greenland to determine sulfate aerosol levels between 1200 and 1850. The researchers were interested in the sulfur emitted by marine phytoplankton, which was initially assumed to be the primary source of atmospheric sulfate in pre-industrial times.

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.

Becky Alexander, Study Senior Author and Professor, Atmospheric Sciences, University of Washington

The researchers intentionally avoided major volcanic eruptions and concentrated on the pre-industrial period, when it was easier to distinguish between volcanic and marine sources.

We were planning to calculate the amount of sulfate 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.

Ursula Jongebloed, Study First Author and Doctoral Student, Atmospheric Sciences, University of Washington

The ice core in the center of the Greenland Ice Sheet records emissions from sources across North America, Europe, and the surrounding oceans. While this result only applies to geologic sources in that area, including volcanoes in Iceland, the authors expect it to be applicable elsewhere.

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

The finding that non-erupting volcanoes leak sulfur at up to three times the initially thought rate is vital for efforts to model past, present, and future climates. Some solar energy is blocked by aerosol particles, which can come from volcanoes, vehicle tailpipes, or factory chimneys.

If natural aerosol levels are higher, it means that the rise and fall of human emissions—peaking with acid rain in the 1970s and then falling with the Clean Air Act and increasingly stringent air quality standards—has had less of an effect on temperature than earlier thought.

Jongebloed says, “There’s sort of a ‘diminishing returns’ effect of sulfate aerosols, the more that you have, the less the effect of additional sulfates. When we increase volcanic emissions, which increases the baseline of sulfate aerosols, we decrease the effect that the human-made aerosols have on the climate by up to a factor of two.”

That implies that recent Arctic warming has revealed more of the full effects of rising heat-trapping greenhouse gases, which are by far the most important control on Earth’s average temperature.

Jongebloed notes, “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 aerosol estimates can greatly enhance global climate models.

Alexander—referring to the gas that smells like rotten eggs—states, “We think that the missing emissions from volcanoes are from hydrogen sulfide. We think that the best ways to improve these estimates of volcanic emissions is to really think about the hydrogen sulfide emissions.”

The US National Science Foundation, NASA and the National Natural Science Foundation of China funded the study.

UW Co-Authors include undergraduate students Sara Salimi and Shana Edouard, doctoral student Shuting Zhai, research scientist Andrew Schauer, and professor Robert Wood.

Other Co-Authors include Lei Geng, a former UW postdoctoral researcher now at the University of Science and Technology of China; Jihong Cole-Dai and Carleigh Larrick at South Dakota State University; Tobias Fischer at the University of New Mexico; and Simon Carn at Michigan Technological University.

Journal Reference:

Jongebloed, U. A., et al. (2023) Underestimated Passive Volcanic Sulfur Degassing Implies Overestimated Anthropogenic Aerosol Forcing. Geophysical Research Letters.


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