The Montreal Protocol has unintentionally slowed global warming and pushed back the first ice-free Arctic summer by 15 years, according to new research

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Efforts to protect the ozone layer have unintentionally benefited Earth’s climate. The Montreal Protocol in particular has not only reduced the “ozone hole” but also slowed global warming.

The treaty, a groundbreaking 1989 international commitment to phase out production of ozone-depleting substances, has also delayed the occurrence of the first ice-free summer in the Arctic by up to 15 years, according to a new analysis published in the Proceedings of the National Academy of Sciences of the United States of America.

The Montreal Protocol grew from the recognition that chlorofluorocarbons (CFCs), used in everyday household products such as air conditioners and refrigerators, were depleting Earth’s protective ozone layer and increasing our exposure to dangerous levels of ultraviolet radiation. But when countries worldwide united to phase out CFCs and other ozone-depleting substances, they didn’t realize that the measure could also reduce climate change. CFCs are greenhouse gases 10,000 times stronger than carbon dioxide (CO₂) in warming power.

Previous studies have highlighted the importance of the Montreal Protocol in protecting the climate. A 2007 article reported that this agreement alone had been more effective than the 1997 Kyoto Protocol, the first international treaty to specifically set legally binding targets to cut emissions. In 2020, the new study’s authors even published a paper suggesting that without CFC emissions, Arctic warming between 1955 and 2005 would have been half as intense. These results spurred the idea of looking into the treaty’s impact on the future of the region’s ice, as well as its past.

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