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.
The Symbolic Moment of an Ice-Free Arctic
Every winter, the surface of the Arctic Ocean freezes, reaching its maximum ice coverage around March. In the summer, most ice melts, reaching its lowest point in September. As the Arctic has warmed nearly 4 times faster than the rest of the planet in the past 4 decades, current projections have suggested the region might see its first ice-free summer between 2030 and 2050.
The first ice-free summer at the North Pole would have a major impact on local ecosystems and populations, as well as on climate. The ice loss would alter carbon cycling and reduce the white surface, which has a cooling effect on the planet by reflecting solar radiation back to space.
“It will be a really big change in the climate system and an important symbolic moment which underlines how much we have impacted the climate,” said coauthor Mark England, a climate scientist at the University of Exeter in the United Kingdom.
England and his colleagues used climate models to calculate how much the reduction of CFC emissions has affected and will continue to affect climate and the Arctic. They simulated two climate systems: one in which the use of CFCs was not phased out and the real-world situation in which CFC emissions were reduced, thanks to the Montreal Protocol.
The researchers estimated that each metric ton of avoided CFC emissions corresponds to 7,000 square meters of avoided Arctic sea ice loss—a huge impact considering that each metric ton of avoided carbon dioxide emissions is estimated to convert to only 3 square meters of retained sea ice. According to their projections, the Montreal Protocol has so far prevented more than half a million square kilometers of sea ice loss.
“The benefits from the Montreal Protocol are not in some faraway future: This is a climate treaty which is already having an impact today and [will continue to do so] over the next few decades,” said England.
One of “Very Few Wins in the Climate Mitigation Space”
Both models were tested under two different scenarios for future emissions of greenhouse gases based on the United Nations’ Intergovernmental Panel on Climate Change (IPCC) framework: a moderate scenario in which emissions peak around 2040 and a “disaster” scenario in which emissions continue to rise throughout the 21st century.
Under the moderate scenario, the researchers found that the Montreal Protocol will have prevented more than 1 million square kilometers of ice from melting in the summer by 2030 and up to 2 million square kilometers by 2040. They estimated that the reduction of CFCs has delayed the first ice-free summer by about 15 years in the moderate emissions scenario and by about 8 years in the disaster scenario.
For England, the analysis showed that international climate agreements can have real-world impact. “We have very few wins in the climate mitigation space,” he said. “But if we can document some of these positive effects, hopefully it can show the public that coordinated climate action is possible and should be celebrated.”
And the Montreal Protocol will continue to positively affect climate well beyond midcentury. The Kigali Amendment to the protocol, for instance, was ratified by nearly 150 UN member states and added hydrofluorocarbons (HFCs) to the list of targeted chemicals. These gases do not cause ozone depletion but are powerful greenhouse gases. According to England and his colleagues, the amendment will reduce global temperatures by between 0.3℃ and 0.5℃ by the end of the century.
The Need for Vigilance in Reducing Carbon Emissions
Despite positive news from the new study, Isaac Vimont, a climate scientist at NOAA’s Earth System Research Laboratories who was not involved in the study, stressed that “we are not off the hook and need to keep drastically reducing emissions of other gases like CO2” to curb global warming.
Vimont was involved in a recent study that showed that even with the Montreal Protocol, emissions of some CFCs are on the rise again. Researchers don’t yet know the sources of these emissions, which are still low enough not to cause immediate worry. But Vimont said we have to remain vigilant.
“As long as the emissions don’t keep going up, [the rise in CFCs is] not going to impact the recovery of the ozone layer at this time,” he said. “But if the emissions continue to rise, they could become significant and impact both the climate and the recovery of the ozone layer.”
—Sofia Moutinho (@sofiamoutinhoBR), Science Writer