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Fifth National Climate Assessment - Read the Report

Supporting ozone layer recovery


Atmospheric concentrations of ozone-depleting gases are tracked at multiple remote sites across the globe, including the observatory at American Samoa (pictured), to determine if controls on these substances will allow recovery of the stratospheric ozone layer. Measurements at these sites previously indicated renewed increases after 2012 in emission and production of an ozone-depleting chemical banned by the Montreal Protocol. Recent findings reveal rapid declines in global and eastern Asian emissions of the potent ozone-depleting gas CFC-11, suggesting that the international response to redouble efforts to minimize emissions and production of this banned substance has been successful. Credit: G. Chensue/NOAA.

Interagency observations and analyses show that emissions of the second-most important ozone-depleting substance are back on the decline after a recent surge.

Atmospheric measurements show that concentrations of ozone-depleting gases are declining in response to global controls on their production and use enacted under the Montreal Protocol of 1987 and its amendments. The decline since the early 1990s in the atmospheric concentration of trichlorofluoromethane (CFC-11), once widely used as a foaming agent and refrigerant, has been an important component of ozone layer recovery.

NOAA and NASA operate coordinated global observing networks that provide the primary data sets related to the ongoing monitoring of concentrations and emissions related to the Montreal Protocol. In 2018, researchers noted that the decline of CFC-11 concentration had slowed by about 50 percent after 2012,1 suggesting increasing emissions and new unreported production despite the global ban. After the increase in emissions was detected, NOAA and NASA researchers worked in collaboration with the U.S. delegation to the Montreal Protocol, including EPA and DOS employees, to shed further light on the issue in support of emissions reductions.

Measurements since the initial announcement in 2018 show a significant drop in global CFC-11 emissions from 2018 to 2019, comparable to the increase in emissions that occurred from 2012 to 2017.2 The decline in global emissions suggests a substantial decrease in unreported CFC-11 production. A companion analysis showed a decline in regional emissions from eastern Asia during this time period.3

These results indicate that the long-term decline in CFC-11 emissions has been restored, and a substantial delay in ozone layer recovery from increased emissions has likely been avoided.


1 Montzka, S.A., Dutton, G.S., Yu, P., et al. An unexpected and persistent increase in global emissions of ozone-depleting CFC-11. Nature 557, 413-417 (2018). https://doi.org/10.1038/s41586-018-0106-2

2 Montzka, S.A., Dutton, G.S., Portmann, R.W. et al. A decline in global CFC-11 emissions during 2018−2019. Nature 590, 428–432 (2021). https://doi.org/10.1038/s41586-021-03260-5

3 Park, S., Western, L.M., Saito, T. et al. A decline in emissions of CFC-11 and related chemicals from eastern China. Nature 590, 433–437 (2021). https://doi.org/10.1038/s41586-021-03277-w