The Montreal Protocol Is Healing Earth’s Ozone Hole

Saving Earth’s protective stratospheric ozone layer from destruction was a major environmental crusade 30 years ago, leading to the regulation of halocarbons and other ozone-depleting substances. But what would Earth look like today if the 1987 Montreal Protocol on Substances That Deplete the Ozone Layer—the international agreement that restricted halocarbon refrigerants, solvents, and aerosol-can propellants—had not been put into force?

The grim outcome has been predicted with an advanced atmospheric chemistry model by researchers led by Martyn P. Chipperfield of the University of Leeds, in England (Nat. Commun. 2015, DOI: 10.1038/ncomms8233). The team found that the Antarctic ozone hole would have grown by an additional 40% by 2013. Their model also predicts that continued use of ozone-depleting substances would have thinned the ozone layer elsewhere around the globe by about 15%. And Arctic ozone holes would have become a regular occurrence. The Leeds model shows that the Antarctic ozone hole is instead on track to disappear by about 2050.

“It is indeed very rewarding to read that the Montreal protocol has already had a positive effect on our planet,” says Mario J. Molina, a chemistry professor at the University of California, San Diego.

In 1974, Molina and F. Sherwood Rowland predicted how halocarbons could chew away Earth’s protective ozone layer by disrupting the sunlight-driven chain reactions that form ozone. Their prediction came true when an ozone hole was first reported over Antarctica in 1985.

For people, the danger from ozone layer depletion is increased exposure to the sun’s damaging ultraviolet radiation. Ozone depletion also contributes to global warming.

With the Montreal protocol in place, halocarbon atmospheric concentrations peaked in 1993 and have since declined. The 1995 Nobel Prize in Chemistry recognized Molina, Rowland, and Paul J. Crutzen (who worked on the role of nitrogen oxides) for their contributions toward averting an environmental catastrophe.

“The ozone story shows that once an environmental problem is identified it is possible for the scientific community to develop the necessary evidence and work together with decision-makers in government to address the challenge,” Molina tells C&EN. “That gives me hope that eventually issues such as climate change will be successfully addressed as well.”