Scientists say the decline, while small, is happening sooner than expected and marks an important milestone in international efforts to protect the layer of Earth’s stratosphere that blocks dangerous ultraviolet radiation.
Scientists said the progress on HCFCs was a sign of hope as humanity struggles to control greenhouse gas pollution.
“This is a remarkable success story of how global policies are protecting the planet,” said Veerabhadran Ramanathan, a climate scientist at the University of California, San Diego and Cornell University, who was not involved in the study.
Just over 50 years ago, researchers noticed a hole in the ozone layer over Antarctica, allowing cancer-causing radiation to reach the Earth’s surface. The main culprits were chlorofluorocarbons (CFCs), which destroy thousands of ozone molecules with a single chlorine atom and can persist in the atmosphere for hundreds of years.
This discovery prompted countries to sign the Montreal Protocol in 1987, agreeing to phase out CFC production. Under the terms of the agreement, wealthy countries were to stop production first, and lower-income countries were to provide financial and technical assistance to stop using the polluting chemicals. CFC production has been banned worldwide since 2010.
But the most common replacements have been HCFCs, compounds that have about one-tenth the ozone-depleting potential of CFCs but can still cause significant damage. The most commonly used HCFCs also have the potential to trap about 2,000 times more greenhouse gases than carbon dioxide over a 100-year period, so in 1992 countries agreed to phase out these chemicals as well.
“The transition has been quite successful,” said Luke Western, a researcher at the University of Bristol and lead author of the study in the journal Nature Climate Change.
The United Nations estimates that global production of ozone-depleting substances in 1990 was reduced by 98 percent. It will take decades for these bans to translate into fewer products being sold and fewer HCFCs in the air, but the Western study, based on data from two global air monitoring programs, suggests that a tipping point may finally be upon us.
According to Western, the climate change impact of HCFCs is expected to peak at about 0.05 degrees Celsius (about one-tenth of a degree Fahrenheit), and atmospheric concentrations of HCFCs are expected to return to 1980 levels by 2080.
“This milestone is a testament to the power of international cooperation,” said Avipsa Mahapatra, head of climate campaigns at the Environmental Research Bureau. “To me, it shows we can achieve much more and gives me hope on the climate front.”
Mahapatra said the success of the Montreal Protocol could galvanize efforts to curb planet-warming pollution, which hit record highs again last year. By setting clear, actionable goals that take into account each country’s needs, the agreement remains the only treaty signed by every country on Earth while galvanizing people to act, he said. The agreement has been credited with helping to avert millions of skin cancer cases worldwide and up to 1 degree Celsius (1.8 degrees Fahrenheit) of warming.
But the work isn’t done yet, Mahapatra says. HCFCs were flawed alternatives to CFCs, but they’re now being replaced by a new class of refrigerants considered climate “super pollutants”: hydrofluorocarbons (HFCs). The Montreal Protocol was amended in 2016 to call for a reduction in the use of HFCs, but they remain heavily used in air conditioners, refrigerators and insulation.
Ultimately, Western said, transitioning away from fossil fuels will be much more complicated than curbing production of ozone-depleting substances. The Montreal Protocol affected relatively small industries and required companies to only change their products, not their entire operations.
When it comes to climate change, “in some ways we’re facing a bigger problem,” Western said.