Global Warming

A key part of the Earth’s ozone layer is failing to heal - and Scientists don’t know why

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 the vast majority of humans live.

There, the scientists found a relatively small but hard-to-explain 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.