By Larry O’Hanlon

Volcanic eruptions are well-known for having the capability to damage local environments, such as the destruction of Pompeii by Mount Vesuvius, but what is less commonly known is the fact that volcanic eruptions can also deplete Earth’s ozone layer. The change in ozone following a volcanic eruption depends on the amount of chlorine in the stratosphere, which is presently still elevated from the human release of chlorofluorocarbons (CFCs) in the twentieth century.

As the CFCs slowly degrade over the coming decades, so too should the volcano’s ozone-destroying power. However, new research shows that the volcanic risk to the ozone layer will persist for decades longer than previously believed.

The study, published in Geophysical Research Letters, a journal of the American Geophysical Union, by scientists from Harvard University and the University of Maryland, College Park (UMD) uses a sophisticated computer model of the response of stratospheric chemistry to volcanoes. The authors find that large volcanic eruptions similar to the 1991 eruption of Mount Pinatubo may reduce the thickness of the ozone layer until year 2070 or even later, much longer than previously thought. This new understanding comes from including in the model bromine-containing very short-lived substances (VSLS), which come from marine plankton and microalgae.

“VSLS bromine is naturally produced and is known to play a significant role in the depletion of lower stratospheric ozone, but we were surprised to see just how sensitive the ozone layer is to a future volcanic eruption using realistic estimates of this bromine source”, said co-author Ross Salawitch of UMD.

“This raised the question: Is this the result of the specific climate change scenario used in the model, or would it occur for a broad range of climate futures?” noted co-author David Wilmouth of Harvard, who directed the research.

The scientists then explored the response of the ozone layer to a Pinatubo-like, future volcanic eruption for four different climate change scenarios. They found that the most optimistic scenarios of low greenhouse gas emissions produced the biggest risk to the ozone layer – and that variations between the scenarios are mostly due to temperature effects and future levels of methane (a greenhouse gas, which also participates in chemical reactions that reduce the ability of chlorine to destroy ozone).

Finally, the study considers one other potentially very significant risk to the ozone layer from volcanic eruptions: chlorine emitted from the volcano itself penetrating up to the stratosphere.

“When we simulate a large volcanic eruption that replicates the ratio of stratospheric hydrogen chloride (HCl) to stratospheric sulfur dioxide (SO 2 ) similar to that seen in satellite observations of recent volcanic plumes, we find that significant ozone depletion occurs throughout this century regardless of Earth’s climate future. If the amount of stratospheric halogen is increased to the level found in ice cores following the eruption of Mount Mazama 7,700 years ago, the threat very quickly becomes dire,” lead author, Eric Klobas stated. He was quick to add “we stress that such an eruption is a very infrequent occurrence”.

Understanding the factors that influence the impact of volcanic eruptions on stratospheric ozone is important because the ozone layer is essential for life on Earth. A reduction of its thickness by even a small fraction can have a significant impact on skin cancer rates, livestock mortality, agricultural yields, and even the lifetime of consumer goods and products.

— Larry O’Hanlon is a freelance science writer, editor and social media manager in New Mexico. He manages the AGU blogosphere. Follow him on Twitter at @Earth2larryo