An international ban on ozone-depleting chemicals preserved the ozone layer and prevented a significant increase in global warming.

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The worldwide ban on chlorofluorocarbons (CFCs) helped avert a dangerous rise in the level of UV radiation reaching Earth’s surface. Tony Shi Photography/Getty Images

A 1987 worldwide ban on ozone-depleting chemicals known as chlorofluorocarbons (CFCs) averted a dangerous rise in the level of ultraviolet radiation (UV) reaching the Earth’s surface.

Without this multilateral environmental agreement, people worldwide would have faced a higher risk of skin and other cancers, eye damage, and possible immune system problems due to excess UV rays.

But a new modeling study from UK researchers suggests that the Montreal Protocol on Substances that Deplete the Ozone Layer also prevented a 2.5°C increase in global warming by the end of the century.

“As well as protecting the ozone layer, the Montreal Protocol has itself been a phenomenally successful climate treaty,” study author Paul Young, PhD, of Lancaster University in the United Kingdom, wrote in a recent post about the research on The Conversation.

“It has controlled not only the emissions of highly potent greenhouse gases like CFCs but, as we have shown, it has avoided additional CO₂ levels through protecting the world’s plant life,” Young said in the article.

In a study in Nature, Young and his colleagues developed a new modeling framework that combined data on ozone depletion, plant damage due to increased UV radiation, the carbon cycle, and climate change.

They looked at three scenarios.

The first is our current situation, with CFCs phased out under the Montreal Protocol. Next is what would have happened if CFCs in the atmosphere had remained at 1960 levels.

Finally is the “world avoided,” which shows what the future would have looked like if CFCs had continued to increase 3 percent each year from the 1970s onward.

Under the last scenario, a continued increase in atmospheric CFCs would have led to ongoing damage to the ozone layer.

This part of the atmosphere shields humans and other life on Earth from harmful levels of ultraviolet radiation from the sun.

The researchers predict that under the “world avoided” scenario, the ozone layer would have collapsed by the 2040s, exposing the planet’s surface to far more UV radiation.

UV rays are harmful not only to people but also to plants. The increase in UV radiation would have caused vast damage to the tissues of plants and restricted their growth.

Plants have many important roles. One of these is storing carbon in their tissues and soils.

The researchers’ model shows that if CFCs had continued to increase, UV damage to plants would have led to hundreds of billions of tons less carbon being stored in forests, other vegetation, and soils by the end of the century.

As a result, the level of CO₂ in the atmosphere would have increased 40 to 50 percent over today’s level — causing an additional 0.8°C of global warming.

CFCs are also potent greenhouse gases. The accumulation of these gases under the “world avoided” scenario would have added another 1.7°C global warming by the end of the century.

This is on top of the increase due to other greenhouse gases and the continued burning of fossil fuels.

Edward Parson, PhD, an environmental law expert and a UCLA School of Law professor, said this new study links climate change and ozone depletion in an “impressive and technically sophisticated way.”

“They’ve found another way that the Montreal Protocol and the elimination — or near-elimination — of ozone-depleting chemicals have done huge good for human welfare and the environment,” he said.

Parson is the author of “Protecting the Ozone Layer: Science and Strategy,” an account of the international cooperation that led to the Montreal Protocol, published in 2003.

However, he is a “little skeptical” about how the paper’s authors framed their modeling.

The “world avoided” is basically the worst-case scenario — what would have happened if the international community had done nothing to address CFCs.

This assumes that countries wouldn’t have stepped up in some other way.

“If there hadn’t been a Montreal Protocol, there might have been some other controls on ozone-depleting chemicals sooner or later,” said Parson, “because [at the time] the harms were clear, and there was already a lot of momentum toward addressing the problem.”

Still, he says the success of the Montreal Protocol is a “remarkable story,” one that he thinks has lessons to teach us about how to address climate change.

Not everyone agrees.

In Young’s post on The Conversation, he cautioned that the problem tackled by the Montreal Protocol was less cumbersome than addressing greenhouse gases and climate change.

“[W]ith just a handful of companies making CFCs and alternative chemicals readily available, the ozone issue was far more straightforward than reducing emissions from fossil fuels,” he wrote.

Fossil fuels, on the other hand, are intertwined with almost every aspect of the global economy and our lives. It’s difficult to imagine a world without them.

Parson, though, points to one particular lesson from the Montreal Protocol — regulations on CFCs were put in place even before alternative technologies to these chemicals were widely available.

The looming threat of these regulations spurred an extraordinary flood of innovative activity, he said, from both CFC producers and industries that used these chemicals.

“There are real possibilities of deploying some of those insights for greenhouse gas controls,” said Parson. “But [climate change] is a bigger, tougher problem, and nobody’s yet put forward a kind of a concrete plan of how it would work.”