Part of ozone layer still not healing
The rescue of the planet’s protective ozone layer has been hailed as one of the great success stories of modern environmental regulation — but on Monday, an international team of 22 scientists raised doubts about whether ozone is actually recovering as expected across much of the world.
“We’ve detected unexpected decreases in the lower part of the stratospheric ozone layer, and the consequence of this result is that it’s offsetting the recovery in ozone that we had expected to see,” said William Ball, a scientist with the Physical Meteorological Observatory in Davos, Switzerland.
In 1987, countries of the world agreed to the Montreal Protocol, a treaty designed to phase out chlorofluorocarbons, or CFCs, responsible for destroying ozone in the stratosphere. The protocol has worked as intended in reducing these substances, and early healing of the ozone “hole” over Antarctica has been subsequently hailed by scientists.
But the study by Ball and his colleagues — a team of scientists including researchers based in the United States, Britain, Canada, Switzerland, Sweden and Finland — focused instead on the lower latitudes where more humans live. The research was published in Atmospheric Chemistry and Physics on Tuesday.
There, the scientists found a relatively small but hard-toexplain decline of ozone in the lower part of the stratosphere, the layer of the atmosphere that extends from about six miles to 31 miles above the planet’s surface, since the year 1998. Meanwhile, the upper stratosphere has been recovering.
“The precise cause of the trend is unknown but could be related to changes to the stratospheric circulation, which has a large influence on how ozone is distributed,” said Ryan Hossaini, an ozone expert at the University of Lancaster in Britain, who was not involved in the study, in an emailed comment. Those, in turn, could be tied to climate change.
There’s also a possibility that a new class of chlorine-containing chemicals not limited by the Montreal Protocol, dubbed “very short-lived substances,” could be contributing to the problem. The most prominent of these substances is dichloromethane, which has a wide range of industrial uses, including as a paint stripper.
Concentrations of the substance have been increasing in the atmosphere, and because of the compound’s relatively short lifetime, it is not regulated now under the Montreal Protocol.
At the same time, though, it’s not clear that there’s enough of it in the atmosphere to be causing what scientists are now observing.