Oceans Are Releasing Stored CFCs Back Into the Atmosphere

• A new study suggests that the oceans will begin releasing CFC-11 by about 2075 and that the chemical will be detectable in the atmosphere by the early part of the 22nd century.
• Climate change will likely exacerbate the situation, turning the oceans into sources of CFC-11 sooner than expected.
• Since the Montreal Protocol was signed in 1987, emissions of CFC-11 have decreased dramatically, but according to some studies, a small amount of the substance is still released into the atmosphere every year.
• While the ozone layer is not currently under global threat, experts believe more research is needed to understand future threats.
• In 1987, world leaders signed the Montreal Protocol with the aim of reducing the amount of chlorofluorocarbons (CFCs) and other hazardous chemicals released into the atmosphere and associated with the depletion of the stratospheric ozone layer that protects life on Earth. Overall, the agreement appears to be producing the intended effects. CFC emissions peaked in the late 1980s, their levels have largely declined, and research has shown that the ozone hole over Antarctica is slowly shrinking.
• However, a new study published in the journal Proceedings of the National Academy of Sciences suggests that the oceans will soon become a source of CFC-11, one of the main chemicals responsible for depleting the ozone layer.
• Currently, the oceans primarily serve as a sink for CFCs, absorbing these water-soluble chemicals (once used in refrigerants, insulation, and aerosol cans), which are then removed from the atmosphere and deposited at the bottom of the oceans. According to the study, however, this will change in about 50 years. Around 2075, we will see a "reverse flow" of CFCs from the ocean to the atmosphere, says lead author Peidong Wang.

Iceberg off the coast of Antarctica. Image by Rhett A. Butler.

• "The atmosphere and the oceans have always been in balance with each other," Wang, a researcher in the Department of Earth, Atmospheric, and Planetary Sciences at the Massachusetts Institute of Technology (MIT), said in an interview. "When [CFC] emissions decrease, the concentration in the atmosphere also decreases, and when the concentration in the oceans is higher than the concentration in the atmosphere, [CFCs] are released [from the oceans]."
• Wang said that the amount of CFC-11 emitted from the oceans in the future will be "rather limited" and is not expected to "have a significant effect on ozone layer recovery." However, he said further research is needed to determine whether ozone layer recovery will be further hindered by other ozone-depleting substances.
• Researchers believe that CFC-11 levels will become “detectable” around 2145.
• "During the first half of the 22nd century, the flux from the oceans will be so large that it might suggest someone is violating the Montreal Protocol, but that could just be due to gas being released from the oceans," said co-author Susan Solomon, the Lee and Geraldine Martin Professor in Environmental Studies in MIT's Department of Earth, Atmospheric, and Planetary Sciences. "This is an interesting hypothesis that we hope will help future researchers correctly interpret what is going to happen."
• In the late 1980s, CFC-11 emissions peaked at approximately 300 gigagrams per year. Although CFC-11 emissions have declined dramatically since the Montreal Protocol came into force, a 2018 study found that emissions have increased by approximately 13 gigagrams per year since 2012 and may be originating in East Asia. A couple of months later, a report by the NGO Environmental Investigation Agency (EIA) found that 18 companies in China were using insulation foam containing CFC-11. Other studies have also highlighted China as a source of CFC-11 emissions.

Great Barrier Reef, Australia. Image by Rhett A. Butler.

• According to Wang, the currently available data may, however, have been overestimated since the amount of CFC-11 absorbed by the oceans each year is increasingly limited as the oceans become increasingly “saturated” with this chemical.
• The study also suggests that climate change will exacerbate the problem, turning the oceans into a source of CFC-11 10 years earlier than expected. This is because rising water temperatures will reduce the oceans' capacity to store CFCs and promote outgassing. However, this is not caused by climate change, the researchers say.
• “We expect the ocean to emit CFCs, even in the absence of climate warming,” Wang said.
• Stratospheric ozone depletion is one of nine planetary boundaries identified in 2009 by a team of international scientists led by Johan Rockström of the Stockholm Resilience Centre and Will Steffen of the Australian National University. Each "boundary" refers to a process in the Earth system that is essential to regulating the planet's stability and resilience, but has an environmental limit within which changes, mostly resulting from human activity, can be tolerated.
• Owen Gaffney, a global sustainability analyst at the Stockholm Resilience Center, says the ozone layer is considered a planetary boundary because it is a “critical part of the Earth system” that protects the planet from dangerous ultraviolet B (UV-B) radiation from the sun and has enabled the evolution of life on Earth.

Coast of South Georgia in the South Atlantic Ocean. Image by Rhett A. Butler.

• “The planetary ozone boundary has been set globally,” Gaffney told Mongabay in an email. “The team determined that it would be unwise to reduce the amount of ozone in a column of the atmosphere by more than 5 percent.”
• The planetary boundary set for the ozone layer is a minimum thickness of 275 Dobson Units ( DU ). According to research , although Earth is currently considered to be within the safe operating range for the ozone layer, the boundary is regionally exceeded in Antarctica each southern spring, when it drops to about 200 DU.
• Gaffney believes that the ozone layer can fully recover thanks to the actions foreseen by the Montreal Protocol but that the “risk of unpleasant surprises” could still put the layer at risk.
• “The ozone depletion was caused by a series of chemicals called CFCs, which contain chlorine and were used in refrigerators,” Gaffney said. “The really curious thing is that these appliances could very well have contained bromine instead of chlorine—the two chemicals are interchangeable. In terms of destroying the ozone layer, bromine is 45 times more aggressive than chlorine. The situation could have been much more serious before we even understood what was happening. It's estimated that 100,000 chemicals are used in the global economy. We don't really know how many of them interact with each other.”
• The new research highlights another risk: the authors say that “we only partially understand the long-term reservoirs for ozone-depleting substances.”