A new study has found that after a mysterious increase in the 2010s, an ozone-depleting chemical is once again in decline. It’s a rare bit of good news, showing that previous research tracking the increase has likely had an impact.
The article, published in the journal Nature on Wednesday, focuses on CFC-11, a chemical that both depletes the ozone and heats the planet. It shows that after a half-decade hiccup where CFC-11 pollution rose, the world’s output of the compound fell in 2019 to levels close to the average seen between 2008 and 2012.
That’s great news for the ozone hole and global temperatures. CFC-11 is a type of chlorofluorocarbon, a class of gases once widely used for refrigeration and air conditioning and as chemical solvents. But the use of those chemicals depleted the ozone layer that protects Earth from the sun’s damaging ultraviolet rays, in addition to being very potent greenhouse gases. (CFC-11 specifically has 5,000 times the global warming potential of carbon in the short term.)
In 1987, world leaders came together to sign the Montreal Protocol, an agreement to ramp down CFC usage. The treaty worked—once leaders pledged to stop using CFCs, manufacturers mostly stopped using them in production, and the ozone has been recovering. But a few years ago, scientists found that between 2013 and 2018, emissions of one type of CFC, CFC-11, actually increased despite global reports of near-zero production since 2010. That suggested that emissions from an unreported source were rising.
“We don’t know for sure what caused the CFC-11 emission increase after 2013, but many experts believe that it was likely from new production of CFC-11 for making new foam [insulation] after the 2010 mandated phase-out of CFC production by the Montreal Protocol,” Stephen Montzka, an atmospheric scientist at the National Oceanic and Atmospheric Administration based in Boulder, Colorado who led the study, said in an email.
To determine how progress on phasing out of CFC-11 has been going since then, Montzka and his co-authors analyzed data from NOAA monitoring laboratories, which measure CFC concentrations by collecting air samples from 13 locations around the world using flasks.
“The flask canisters are shipped back to my lab in Boulder and are analyzed on custom laboratory instrumentation to determine the concentration of CFC-11 and other gases,” said Montzka.
The authors found that atmospheric levels of CFC-11 are decreasing again. Specifically, they found that in 2019, the world emitted 57,320 U.S. tons of the gas in 2019, which is nearly 20,000 U.S. tons less than 2018's output. Put simply, we’re back on track.
Another new study published in the same issue of Nature analyzed the same data from NOAA’s monitoring sites and found that about 60% of that reduction was the result of emissions cuts from eastern China specifically—probably the result of local crackdowns on factories in mid-2019.
“It was reported that Chinese authorities reacted, making seizures of CFCs, arrests and destroying production facilities,” Luke Western, an atmospheric scientist at the University of Bristol and the second study’s lead author, wrote in an email.
Those crackdowns came in response to 2019 research also led by Western showed that between 40% and 60% of the unexpected rise in emissions in the 2010s was likely from illicit use of CFC-11 at factories in the coastal province Shandong and the inland province Hebei, which were producing foam for refrigerators and building insulation.
To see if those actions made a difference, the researchers specifically examined data on CFC-11 concentrations from two measurement stations in East Asia. By using computer models that simulate the atmospheric transmission patterns of gases, they were able to determine where exactly emissions were occurring. They determined that in eastern China, CFC-11 output in 2019 was about 11,000 U.S. tons less than it was in 2018, meaning virtually all of the region’s illicit new pollution got wiped out.
The researchers still don’t know where the remaining 40% or so of the mysterious rise in CFC-11 emissions between 2013 and 2018 came from, but thankfully, it looks like that also got wiped out between 2018 and 2019. Western said future research might help them determine the culprit, but that his priority—and the priority of signatories to the Montreal Protocol—is pinpointing the source of all remaining CFC emissions to eradicate them.
“The main focus is on expanding the current measurement coverage to ensure any future challenges can be addressed,” said Western.
Montzka said that rapidly ending CFC-11 emissions “will ensure that the ozone layer heals as fast as is possible.” That’s important, since the layer blocks harmful ultraviolet radiation that can harm plant and animal life and can also cause sunburn and eye disease for humans. Less CFC-11 also means less warming. But at the same time, Montzka noted that the compound isn’t the main contributor to the climate crisis—though it’s potent, emissions are nowhere near the scale of other greenhouse gases like carbon dioxide, methane, and nitrous oxide. We’ve also got to curb emissions of other greenhouse gases, including the ones emitted by ozone-depleting chemicals’ replacements, to secure a livable future.