Protecting the Ozone: 25 Years of the Montreal Protocol

How a universal treaty is still working to protecting the ozone layer a quarter-century later.
Cloudy Sky photo by Reun Yreun

Photo by Reun Yreun.

September marked the 25th anniversary of the Montreal Protocol on Substances that Deplete the Ozone Layer—the most successful international treaty on environmental regulation to date.

The ozone layer of Earth’s stratosphere filters the sun’s hazardous ultraviolet radiation (UVR). Exposure to UVR has been linked to a range of health problems, including skin cancer, eye damage, and suppression of the immune system. UVR can damage crops and have devastating effects on marine life.

The Montreal Protocol involved phasing out manufacture of chemical substances—such as the chlorofluorocarbons (CFCs) found in aerosols and refrigeration systems—which were destroying the ozone layer.

The ratification of the protocol in 1987 was the result of unprecedented international cooperation. An important component was application of the “precautionary principle”—taking action based on scientific evidence, but short of absolute proof. Consumer pressure and bipartisan support in the U.S. Congress helped.  Successful implementation of the protocol included incentives for industries to comply, financial support for developing countries, and restricted trade with countries that didn’t sign the agreement.

Despite initial resistance by industry giants such as DuPont—the world’s largest CFC producer—the protocol became the first United Nations treaty to achieve universal ratification.
By 2009, 98 percent of the chemicals listed by the protocol had been phased out. According to a report from the United Nations’ Ozone Secretariat in 2010, atmospheric levels of ozone-depleting substances are going down, and with implementation of the protocol’s provisions, the ozone layer should return to pre-1980 levels by the middle of this century.

A recent study of the Montreal Protocol’s positive effects was published in the journal Photochemical and Photobiological Sciences. It modeled two projections of skin cancer rates, one based on compliance with the protocol and the other on noncompliance, and found that by 2030 compliance will have reduced skin cancer by 16 percent.


  • It takes humility to recognize that what we’ve called progress isn’t always for the better. Sometimes nature’s original idea was a better one.

  • Climate change is already increasing the likelihood of weather extremes—like the droughts and heat waves we’ve seen in recent years—according to a new report by one of NASA’s top climate scientists.

  • Oil companies—and many of our political leaders—see melting sea ice as an opportunity to drill deeper. Fortunately, you don’t have to occupy an Arctic drilling platform to join the growing movement of people who are putting themselves on the line for our planet’s future.