The ozone hole makes a comeback

Are we witnessing a new chapter in the story of the ozone hole over Antarctica? The past three years have seen the re-emergence of large, long-lived ozone holes, which seem to be expanding. This raises questions over whether global efforts to heal the ozone layer have been successful. New findings, published in the journal Nature Communications, suggest that the ozone has not been recovering over the last few decades as many forecast it would.

Analysing monthly and daily ozone readings from 2004 to 2022, the researchers found that the ozone hole contains significantly less ozone than it did. “Our analysis concluded with the data from 2022, but as of today, the ozone hole in 2023 has already surpassed the size of the three previous years: by the end of last month, it exceeded 26 million square kilometres,”  said Hannah Kessenich from the University of Otago.

Ozone levels are decreasing

In 1987 the United Nations approved the Montreal Protocol, banning chlorofluorocarbons (CFCs), which scientists had discovered were depleting the ozone layer. It was hailed as a major environmental victory. Earlier this year a UN report projected that the ozone would return to 1980’s levels by 2040.

But it’s now becoming apparent that it’s not just CFCs at work. Some scientists have suggested ozone depletion might also be due to a low-pressure system of cold westerly winds – the Antarctic polar vortex. The pattern since 2004 is that the early spring shows indications of ozone-hole recovery, but by October the middle stratosphere is exhibiting significant ozone reduction, amounting to a 26% loss in the core of the ozone hole. Other scientists say that ozone holes have been caused by the 2019 wildfires and volcanic eruptions.

There is also the possibility that the role of CFCs has been overestimated, at the expense of decadal variations in ozone concentrations over the South Pole.

Understanding ozone variability is important because of the major role Antarctic stratospheric ozone plays in climate variability across the Southern Hemisphere. Climate change may have incited new sources of ozone depletion, and the atmospheric abundance of several CFCs has recently been on the rise.

In other words, whilst our attention was turned elsewhere, the ozone hole has been making a comeback.