Global CFC emissions now declining again as expected under the Montreal Protocol

February 11th, 2021

In 2018, a paper published in Nature (Montzka et al., 2018), using observations of CFC-11 concentrations in the atmosphere from NOAA’s global monitoring network, largely from Mauna Loa, Hawaii, but also including data from Cape Grim, Tasmania, revealed surprisingly that global emissions of CFC-11 had stopped declining by 2007 and started to increase again (2008-2017, Figure 1), contrary to expectations under the Montreal Protocol.

It was concluded that new, illegal production of CFC-11 was underway in east Asia, most likely escaping to the atmosphere during CFC production and during the subsequent manufacture of insulating foams incorporating CFCs. If these CFC emissions were to continue indefinitely there would be a significant delay in the predicted recovery of upper-atmospheric ozone over Antarctica (the Antarctic ozone ‘hole’).

In a subsequent 2019 paper in Nature (Rigby et al., 2019), a team of scientists from Europe, USA, South Korea, Japan, China and Australia (AGAGE and affiliates) confirmed that 50% or more of the newly increased global CFC-11 emissions were from east Asia, specifically from eastern China. The existing global CFC monitoring networks (NOAA, AGAGE) were unable to locate the other missing CFC-11 sources, but were able to eliminate Europe, North America and Australia (Fraser et al., 2020) as significant contributors.

Following the initial discovery in 2018-2019, the world’s nations recognized that this was a major test for their previously highly successful Montreal Protocol and called for immediate action. China quickly announced renewed enforcement and inspections measures. NOAA and AGAGE scientists began looking for further results.

Renewed analysis of post-2017 NOAA and AGAGE atmospheric data (including data from cape Grim) began in urgency and it was soon clear that global emissions had commenced to fall again, dropping sharply between 2018 and 2019 (Figure 1). The abrupt turnarounds in global and east China CFC-11 emissions were detected in both networks and the results published in Nature in February 2021 (Montzka et al., 2021; Park et al., 2021).

Global CFC chart

Figure 1: Global CFC-11 emissions based on atmospheric measurements from the AGAGE global network (Montzka et al., 2021), compared to expected emissions under the Montreal Protocol; extrapolated emissions to end of 2019 are based on AGAGE global CFC-11 annual mean concentrations for 2019 and 2020.

The twin papers indicate that efforts to address the first known substantive violation of the Montreal Protocol, tasked with ensuring stratospheric ozone layer recovery, are working.

‘This was a major test for the Montreal Protocol, which it appears to have passed, and this is a great example of how important early warnings from observational systems can be’ said NOAA scientist Dr Stephen Montzka, who led the research team that first documented the problem in 2018.

The new results show that from 2018 to 2019, global emissions of CFC-11 decreased by about 25-30%. Current global emissions now appear to have returned to pre-2012 levels. East China emissions in 2019 dropped 33% compared to 2014-2017, returning to pre-2013 levels. It is surprising to see the rapid turn-around in emissions as indicated by the data, globally and in eastern Asia. Even more remarkable is that the decline over the past two years was as large as, or perhaps bigger than, the original rise.

There are some looming challenges for the global trace gas monitoring networks. The coming years will see the complete phase-out of two families of chemicals that have replaced the CFCs – hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), which do less damage to the ozone layer, but, like CFCs, are very potent greenhouse gases that contribute to climate change.  Similar evidence-based (atmospheric measurements) verification showing that the international community is abiding by their agreements to phase-out HFCs and HCFCs looms as a coming test of the Montreal Protocol, but one that must be passed to help minimize future climate change.

It is clear that the global coverage of the atmospheric observing networks for synthetic greenhouse gases, such as the HFCs, needs to be expanded, so that likely emissions from India, Russia, Africa and South America can be added to those from Europe, North America, China and Australia, thereby reducing the current uncertainties surrounding the magnitude and location of sources of synthetic greenhouse gas emissions.


Fraser, P. J., B. L. Dunse, P. B. Krummel, L. P. Steele, B. Mitrevski, C. E. Allison, N. Derek, A. J. Manning, A. Redington and M. Rigby, Australian chlorofluorocarbon (CFC) emissions: 1962-2017, Environ. Chem., 17(8), 525-544, 2020,
Montzka, S.A., G. S. Dutton, P. Yu, E. Ray, R. W.  Portmann, J. S. Daniel, L. Kuijpers, B. D. Hall, D.  Mondeel, C. Siso, J. D. Nance, M. Rigby, A. J.  Manning, F. Moore, B. R. Millerand J. W. Elkins (2018). An unexpected and persistent increase in global emissions of ozone-depletion CFC-11. Nature 557, 413-417, 2018,
Montzka, S. A., G. S. Dutton, R. W. Portmann, M. P. Chipperfield, S. Davis, W. Feng, A. J. Manning, E. Ray, M. Rigby, B. D. Hall, C. Siso, J. D. Nance, P. B. Krummel, J. Mühle, D. Young, S. O’Doherty, P. Salameh, C. Harth, R. G. Prinn, R. F. Weiss, J. W. Elkins, H. Walter-Terrinoni and C. Theodoridi, A decline in global CFC-11 emissions during 2018-2019, Nature,, published February 2021.
Park, S., L. M. Western, T. Saito, A. L. Redington, S. Henn, X. Fang, R. G. Prinn, A. J. Manning, S. A. Montzka, P. J. Fraser, A. L. Ganesan, C. M. Harth, J. Kim, P. B. Krummel, Q. Liang, J. Muhle, S. O’Doherty, H. Park, M. K. Park, S. Reimann, P. K. Salameh, R. F. Weiss and M. Rigby, A decline in emissions of CFC-11 and related chemicals from eastern China, Nature,, published February 2021.
Rigby, M., S. Park, T. Saito, L. Western, A. Redington, X. Fang, S. Henne, A. Manning, R. G. Prinn, G. Dutton, P. J. Fraser, A. L. Ganesan, B. Hall, C. Harth, J. Kim, K-R. Kim, P. B. Krummel, T. Lee, S. Li, Q. Liang, M. Lunt, S.A. Montzka, J. Muhle, S. J. O’Doherty, M.-K. Park, S. Reimann, P. Salameh, P. Simmonds, R. Tunnicliffe, R. F. Weiss, Y. Yokouchi and D. Young, An increase in CFC-11 emissions from China inferred from atmospheric observations, Nature, 569, 546-550, 2019,