Thanks to the 1987 Montreal Protocol that banned the production of ozone-depleting chlorofluorocarbons (CFCs), global efforts to prevent the depletion of the planet’s ozone layer have been surprisingly successful. Although a full recovery isn’t expected until the middle of the century, the ozone layer is now gradually replenishing, and the infamous ozone hole above Antarctica is slowly closing. However, new evidence underlines how the world’s volcanoes are hindering humanity’s efforts.

‘It’s important to recognise that volcanoes do not themselves destroy ozone, but rather enhance human-caused ozone loss,’ explains Catherine Wilka, from the Department of Earth, Atmospheric, and Planetary Sciences at Massachusetts Institute of Technology. When a volcano erupts, she explains, sulphuric acid particles are released. These cause chlorine in the stratosphere – such as that released by CFCs – to convert into a form where it is capable of destroying ozone.

Wilka and colleagues used climate model simulations to calculate the extent to which major volcanic eruptions have affected the ozone layer. The eruption of Mount Pinatubo in the Philippines in 1991 is a standout example from 1979-1998, when the ejected particles significantly escalated ozone depletion. From 1999 onwards, eruptions haven’t further harmed the layer but they have slowed its recovery. This indicates that it will be during periods of minimal volcanic activity that the Protocol will have the most impact in significantly repairing the ozone layer.

‘We had a particularly quiet period from the mid 1990s to about 2004, and have had a few moderate size eruptions since then,’ recalls Wilka. ‘When we calculate ozone recovery trends since 1998, the recovery is flatter than it would be if we’d had a volcanically active period in the early 2000s and a quiet period right now. That doesn’t mean the ozone layer isn’t recovering: it means that the recovery due to decreasing stratospheric chlorine will take longer to emerge from the natural variability. However, it’s important to stress that the ozone layer will continue to recover throughout the 21st century as long as we adhere to the Montreal Protocol, regardless of volcanic eruptions.’

This was published in the October 2018 edition of Geographical magazine

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