Though small, that decline comes sooner than expected, scientists say — and it represents a significant milestone for the international effort to preserve the layer of Earth’s stratosphere that blocks dangerous ultraviolet sunlight.
As humanity struggles to control greenhouse gas pollution that has already pushed global temperatures to unprecedented highs, scientists said the progress on HCFCs is a hopeful sign.
“This is a remarkable success story that shows how global policies are protecting the planet,” said Veerabhadran Ramanathan, a climate scientist at the University of California at San Diego and Cornell University who was not involved in the new study.
Just over 50 years ago, researchers realized that a hole was forming in the ozone layer over Antarctica, allowing cancer-causing radiation to reach Earth’s surface. The main culprits were chlorofluorocarbons (CFCs), which could destroy thousands of ozone molecules with a single chlorine atom and linger in the atmosphere for hundreds of years.
The discovery prompted countries to sign the 1987 Montreal Protocol, agreeing to phase out production of CFCs. Under the terms of the agreement, rich countries would halt production first and provide financial and technical assistance to low-income nations as they also moved away from the polluting chemicals. Production of CFCs has been banned globally since 2010.
But the most common replacements were HCFCs — compounds that have about one-tenth of the ozone-depleting potential of CFCs, but could still cause significant damage. The most commonly used HCFC also has roughly 2,000 times the heat-trapping potential of carbon dioxide over a 100-year period. So in 1992 nations agreed they would abandon these chemicals as well.
“The transition has been pretty successful,” said University of Bristol researcher Luke Western, the lead author of the Nature Climate Change study.
The United Nations estimates that the world has curbed 98 percent of the ozone-depleting substances being produced in 1990. It takes decades for those manufacturing bans to translate into fewer products sold and fewer HCFCs in the atmosphere. But Western’s research, which drew on data from two global air monitoring programs, shows that turning point has finally arrived.
HCFCs’ contribution to climate change peaked at about 0.05 degrees Celsius (almost a tenth of a degree Fahrenheit), Western said, and their abundance in the atmosphere is expected to return to 1980 levels by 2080.
“This milestone is a testament to the power of international cooperation,” said Avipsa Mahapatra, director of the Environmental Investigation Agency’s climate campaign. “To me, that signals potential to do a lot more, and it gives me climate hope.”
Mahapatra said the success of the Montreal Protocol could inspire efforts to curb planet-warming pollution — which hit another record high last year. By setting clear, enforceable targets that were cognizant of each nation’s needs, she said, the agreement propelled people to take action while remaining the only treaty signed by every country on Earth. It is credited with helping the world avoid millions of skin cancer cases and as much as a full degree Celsius (1.8 degrees Fahrenheit) of warming.
But the work is not done, Mahapatra said. Much as HCFCs were a flawed substitute for CFCs, they have now been replaced by a new class of refrigerants — hydrofluorocarbons (HFCs) — that are considered climate “super pollutants.” Although the Montreal Protocol was amended in 2016 to call for a reduction in use of HFCs, they are often used in air conditioners, refrigerators and insulation.
Ultimately, transitioning away from fossil fuels will be far more complex than curbing the production of ozone-depleting substances, Western said. The Montreal Protocol affected a relatively small industry, and it required companies only to change their products — not their entire businesses.
With climate change, “You’re up against a bigger beast in some ways,” Western said.
