Strangely, here’s a good piece of news about the work humanity has done to save the world. A major international agreement to phase out ozone-harming chemicals has also helped the world avoid a whopping extra 4.5 degrees Fahrenheit (2.5 degrees Celsius) of global warming by the end of this century, according to a new study.
That study, published in Nature on Wednesday, is a little unusual in that it doesn’t look at an existing problem. Rather, it floats a hypothetical scenario, trying to imagine a world where the groundbreaking international agreement to protect the ozone doesn’t exist. It shows that in a world without that agreement in place, the climate would also suffer.
The current state of international climate policy can make anyone think that the world can’t come to an agreement on anything. But the Montreal Protocol is proof good things can happen. The treaty was inked in the 1980s to phase out common chemicals known as chlorofluorocarbons or CFCs. Those chemicals—until then, widely used in refrigerators, air conditioners, and aerosol cans—destroy the ozone layer. In a rare bit of good news, the treaty was a success: Some 30 years after it entered into force, the ozone layer is showing signs of recovery. It’s expected to return to pre-1980s levels by the mid-2050s after CFCs have largely left the atmosphere.
Other research has looked at what the new study’s authors refer to as the “world avoided”—a world where we kept using CFCs with abandon and “the ozone layer drastically thins and very high levels of UV reach the Earth’s surface”—when it comes to skin cancer and public health. But CFCs and other ozone-depleting chemicals are also greenhouse gases, Paul Young, the study’s lead author, wrote in an email. They’ve contributed to a small portion of the warming we’ve seen, and they also have other impacts on the climate system. That’s the focus of the new study.
“We were interested in what [continuing CFC use] would mean for vegetation,” Young said. “Vegetation (i.e., plants and trees) is important as it takes up some of the carbon dioxide we emit, which is the main driver of climate change. But vegetation gets damaged by high UV and it therefore absorbs less carbon.”
It turns out that protecting that vegetation from UV rays and avoiding the greenhouse gas effect of CFCs is pretty damn important. In their models, Young and his colleagues found that without the Montreal Protocol, CFCs would be on track to contribute an additional 2.1 degrees Fahrenheit (1.7 degrees Celsius) of global warming by the end of this century through their greenhouse effect alone. The results show the high UV rays would damage plants, trees, and other carbon sinks, leading to an additional 165 to 215 parts per million of carbon dioxide in the atmosphere. (For comparison, atmospheric carbon dioxide currently sits at around 420 ppm.) Overall, that would contribute another whopping 1.4 degrees Fahrenheit (0.8 degrees Celsius) of heating by 2100. Those combined effects on the climate would make swaths of the planet unbearably hot even if we magically stopped carbon emissions tomorrow.
It may sound like we’ve totally avoided ozone disaster, but Young said that some forms of geoengineering—a radical idea to cool the planet by spraying reflective particles into the atmosphere that’s gaining increasing traction in some circles—need to be further studied to better understand their effects on the ozone and, by extension, plant life. And despite the incredible amount of warming avoided by the Montreal Protocol, Young cautioned drawing too many parallels between current efforts to lower carbon dioxide emissions and the success of phasing out CFCs.
“We must remember that the Montreal Protocol was dealing with a handful of chemicals, made by a handful of companies, and for which there were replacements readily available,” he wrote. “Despite some resistance from the companies, and the existence of some cranks denying the evidence, the ozone layer issue was ultimately a tractable one. Fossil fuels, on the other hand, are a far more complex issue, whose use permeates our lives more deeply and whose reduction will not just be a straight swap with another chemical.”
But that’s not a reason to give up the fight, he continued.
“Perhaps the hope from the Montreal Protocol is that it has been a tremendous success story: science identified a threat and the world agreed and acted on that threat,” Young said. “Let’s hope our next experiment will be comparing our Paris Agreement-compliant world with a ‘world avoided’ where we ignored the need to get to net zero emissions.”