Twenty years after the Montreal Protocol came into effect to regulate substances that deplete the ozone layer, the annual ozone hole above Antarctica shows no signs of recovery.

A feature article and editorial in Nature today explain why this is so, and why the Montreal Protocol has been a unique success nonetheless.

As things stand, scientists expect the first signs of recovery of springtime ozone depletion in the polar stratosphere around the year 2065. Outside polar regions, where chemical ozone destruction is less pronounced but potentially harmful to human health, it appears as if ozone levels are beginning to increase.

Globally, the recovery of ozone will occur in a changing atmospheric environment. Greenhouse gases have a cooling effect on the stratosphere, and climate change is likely to also alter atmospheric transport and circulation patterns.

What this means for the ozone layer is not exactly clear. It appears that the changes will in some places delay its recovery, while elsewhere they might lead to a ‘super-recovery’ of ozone.

But not only must models of ozone loss and recovery factor in global warming – abnormally low stratospheric ozone has also a marked effect on climate change here and now. Most strikingly, extreme seasonal ozone depletion over Antarctica seems to explain why the Antarctic Peninsula is warming at an alarming rate while the rest of the continent has actually cooled over the last 30 years.

Quirin Schiermeier

Image: View of the South Pole from NASA’s TOMS (Total Ozone Mapping Spectrometer) satellite. Credit: NASA