Ozone Layer Isn't Healing After All—and Depletion May Be More Harmful Than Ever

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Earth's atmosphere, as pictured from the International Space Station. The stratosphere appears white. Chris Hadfield/NASA

Updated | The Earth's ozone shield continues to thin across much of the planet, scientists have discovered. With the decline sited over some of the most populous places on Earth, this decrease could be even more damaging than the Antarctic hole.

While the famous hole in the ozone layer may be shrinking, its recovery has been offset by this unexpected decrease in other parts of the atmosphere.

Shield against deadly UV radiation

Ozone forms in the section of the atmosphere called the stratosphere. It blocks a large amount of deadly UV radiation from the sun, which can damage the DNA of animals, plants and humans.

In the 1980s, scientists discovered a large hole in the ozone layer, exposing the Antarctic to far higher levels of UV radiation than other parts of the planet. Aerosols and refrigerators were blamed for spewing ozone-depleting substances like chloroflurocarbons (CFCs). The Montreal Protocol agreement of 1987 led to the phasing out of CFCs and the first signs of repair in the upper stratosphere over the Antarctic.

But, for reasons as yet unknown, ozone seems to be disappearing from some parts of the lower stratosphere, a study published in Atmospheric Chemistry and Physics has found.

The area affected stretches from latitude 60N—a line which traces the globe through Canada and Russia—all the way down to 60S, which sits above Antarctica.

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Antarctic ozone depletion, imaged in 2009. NASA Goddard

Study co-author Joanna Haigh, co-director of the Grantham Institute for Climate Change and the Environment at Imperial College London, explained in a statement: "The potential for harm in lower latitudes may actually be worse than at the poles. The decreases in ozone are less than we saw at the poles before the Montreal Protocol was enacted, but UV radiation is more intense in these regions and more people live there."

Ozone-friendly replacement could be a factor

Researchers analysed information from 11 different datasets to create a subtle model of the ozone over the last 30 years. They found that the amount of ozone in parts of the lower stratosphere was decreasing.

William Ball from ETH Zurich and PMOD/WRC Davos, who led the analysis, said: "The study is an example of the concerted international effort to monitor and understand what is happening with the ozone layer — many people and organisations prepared the underlying data, without which the analysis would not have been possible."

The results were a surprise to authors and defy the expectations of current models. Ball said: "The finding of declining low-latitude ozone is surprising, since our current best atmospheric circulation models do not predict this effect. Very short-lived substances could be the missing factor in these models."

Chemicals used as solvents, paint strippers and degreasing agents could be part of the explanation, the researchers think. One such chemical is even used to make a CFC replacement.

Another explanation comes from climate change, where patterns of atmospheric circulation are disrupted. Ozone could be carried away from certain areas of the planet as atmospheric conditions continue to change.

Research should be focused on getting better, more subtle, data on ozone decline, the authors say. This will help determine the factors still damaging the ozone—and help work towards solutions.

This article has been updated to include further comment from William Ball.