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The Montreal Protocol Is Healing Earth’s Ozone Hole

Climate Science: Study shows what the planet’s protective ozone layer might look like if destructive halocarbons had not been phased out

by Stephen K. Ritter
May 28, 2015 | APPEARED IN VOLUME 93, ISSUE 22

Credit: Nat. Commun.
The Antarctic ozone hole (values in dobson units with greater depletion in blue) as it would have been with (top) and without (bottom) the Montreal protocol.
Credit: Nat. Commun.
The Antarctic ozone hole (values in dobson units with greater depletion in blue) as it would have been with (top) and without (bottom) the Montreal protocol.

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.”

Credit: Nat. Commun.
The Leeds model predicts that the Montreal Protocol has prevented an increase in Earth’s surface ultraviolet index of about 20% in Antarctica and about 5% in the tropics.


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Harsha Godiwalla (May 28, 2015 8:20 AM)
Hi, in addition to halocarbons, need to control the toxic chemicals generated during any type of plastic product manufacture and recyling of the plastic products.
Tom Hard (June 3, 2015 3:17 PM)
The article's statement that ozone depletion contributes to global warming is incorrect. That statement is based on the increased ultraviolet radiation that would reach the earth's surface if stratospheric ozone is removed. But the statement doesn't take into account ozone's absorption of outgoing infrared radiation from the earth's surface. Ozone's infrared absorption band is near the earth's blackbody radiation peak. Atmospheric absorption of outgoing radiation in that region raises the earth's average temperature. Thus ozone depletion makes both positive (ultraviolet) and negative (infrared) contributions to global warming. The infrared contribution is larger, so the net result of ozone depletion is global cooling.
Steve Ritter (June 8, 2015 6:47 AM)
Thanks for your comment, Tom. According to Martyn Chipperfield, you are right removing ozone in the stratosphere does not lead to global warming. The main effect of ozone on surface temperature is as a greenhouse gas absorbing in the infrared. However, CFCs are potent greenhouse gases, so the overall effect of depleting the ozone layer--emitting CFCs and causing ozone loss, has enhanced surface warming. As Mario Molina has described in recent years, the Montreal Protocol has been helping to reverse this.

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