CFCs, greenhouse gases, and naturally occurring emissions of halogens will shape how volcanoes impact the ozone layer into the next century
The next major volcanic eruption could kick-start chemical reactions that would seriously damage the planet’s already besieged ozone layer.
The extent of damage to the ozone layer that results from a large, explosive eruption depends on complex atmospheric chemistry, including the levels of human-made emissions in the atmosphere. Using sophisticated chemical modeling, researchers from Harvard University and the University of Maryland explored what would happen to the ozone layer in response to large-scale volcanic eruptions over the remainder of this century and in several different greenhouse gas emission scenarios. The research was published recently in Geophysical Research Letters.
The Earth’s stratosphere is still recovering from the historic release of chlorofluorocarbons (CFCs) and other ozone-depleting chemicals. Even though CFCs were phased out by the Montreal Protocol 30 years ago, levels of chlorine-containing molecules in the atmosphere are still elevated. Explosive volcanic eruptions that inject large quantities of sulfur dioxide into the stratosphere facilitate the chemical conversion of chlorine into more reactive forms that destroy ozone.
Researchers have long known that when concentrations of chlorine from human-produced CFCs are high, ozone depletion will result following a volcanic eruption. When levels of chlorine from CFCs are low, volcanic eruptions can actually increase the thickness of the ozone layer. But exactly when this transition happens — from eruptions that deplete ozone to eruptions that increase ozone layer thickness — has long been uncertain. Previous research has put the window of the transition anywhere between 2015 to 2040.
The Harvard researchers found that volcanic eruptions could result in ozone depletion until 2070 or beyond, despite declining concentrations of human-made CFCs.
“Our model results show that the vulnerability of the ozone column to large volcanic eruptions will likely continue late into the 21st century, significantly later than previous estimates,” said David Wilmouth, who directed the research and is a project scientist at the Harvard John A. Paulson School of Engineering and Applied Sciences and the Department of Chemistry and Chemical Biology.
So, why is this shift happening so much later than previously thought?
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