When a volcano erupts, a massive column of ash and gas will shoot up, sometimes propelling sulfur gasses all the way to Earth's stratosphere. Gases react there with water to form aerosol particles that can reflect some of the sun's rays and heat back out into space, and in that way act as a sort of temporary sunscreen for Earth, cooling the planet down.
The problem is that man-made changes to our atmosphere seem to be negating some of the volcanoes' cooling effects, and as the planet gets warmer, the problem could get worse. According to new research in the Journal of Geophysical Research: Atmospheres, climate change could hinder volcanoes' ability to cool the Earth.
"We have a computer model of the volcanic plume," said Thomas Aubry, PhD candidate at the University of British Columbia, an author of the paper. "This computer model gives you the plume height and the input required for the eruption intensity and atmospheric condition. [Using current eruption and atmospheric data], we used this model to ask if the plume height left the troposphere or not." (The troposphere is the lowest level of Earth's atmosphere.)
Warmer air resulting from increased CO2 emissions cause the atmosphere to expand, so the sulfur gasses don't necessarily reach the point where they are captured by the stratosphere. Instead, they remain in the expanding troposphere, possibly causing more issues here on the ground, and never get to act as a sun shield for our planet.
"I think there would be many more potential consequences," said Aubry. "The paper is motivated by this climate problem and in terms of risk management."
The researchers noticed that volcanism has played a very small part in slowing down the rate at which the planet is heating up, which is still happening at breakneck speed. The last 10-to-15 years have seen a number of "stratospheric" volcanic eruptions, Aubry noted, but the benefits don't seem like they're going to last. The team determined that there may be a drop of two-to-twelve per cent of sulfur gasses in the atmosphere over the next century, and possibly a 12-to-25 per cent drop by the 23rd century.
Understanding all of this will help scientists learn more about other times in Earth's history when the climate underwent major changes—including how volcanoes might have contributed to a particularly intense Ice Age about 700 million years ago, sometimes called "Snowball Earth," in which the planet was almost entirely locked up in ice—but they'll also make for better models of where we're going in the future.
"We don't expect to see a huge increase global warming rate due to this feedback," said Aubry, adding that all of this should nonetheless form part of the discussion around climate change. "We think it's still significant enough to matter."
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Correction: An earlier version of the piece said that the researchers determined that there will be a drop of two-to-twelve per cent of sulfur gasses in the atmosphere over the next century. The word "will" has been changed to "may," to better reflect that this is a prediction.