the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
A Method for Calculating Offsets to Ozone Depletion and Climate Impacts of Ozone-Depleting Substances
Stephen A. Montzka
Stephen O. Andersen
Richard Ferris
Abstract. By phasing out production and consumption of most ozone depleting substances (ODSs), the Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol) has avoided consequences of increased ultraviolet (UV) radiation, and it will restore stratospheric ozone to pre-1980 conditions by mid-century, assuming compliance with the phaseout. However, several studies have documented an unexpected increase in emissions and unreported production of trichlorofluoromethane (CFC-11) and other ODSs that occurred after 2012 despite production phaseouts under the Montreal Protocol. Furthermore, because most ODSs are powerful greenhouse gases there are significant climate protection benefits in collecting and destroying the substantial quantities of historically allowed products under the Montreal Protocol that are contained in existing equipment and products and referred to as ODS “banks”. Here we present a framework for considering offsets to ozone depletion, climate forcing, and other environmental impacts arising from this or other occurrences of unexpected emissions and unreported production of Montreal Protocol controlled substances. We also show how this methodology could be applied to the destruction of banks of controlled ODSs and GHGs, or to halon or other production allowed under a Montreal Protocol Essential Use Exemption or emergency exemption. Further, we explore a range of potential actions that could offset the ozone depletion, climate, and other environmental impacts arising from instances of unexpected emissions or unreported production should Montreal Protocol Parties agree require remedial action.
Gabrielle B. Dreyfus et al.
Status: open (until 01 Apr 2023)
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RC1: 'Comment on acp-2023-53', Anonymous Referee #1, 15 Mar 2023
reply
In this manuscript, the authors propose a framework of methods to evaluate impacts of unexpected emissions of ODS on ozone depletion and climate change. The article provides an interesting summary of methods and metrics proposed in the literature for evaluating these impacts and suggest a list of actions for offsetting them. The article is well written and documented, however I wonder if it fits in the scope of Atmospheric Chemistry and Physics journal since it is very qualitative and provide few quantitative estimates of the impact of the various proposed options for offsetting impacts of unexpected ODS emissions. In addition, the quantitative values cited in section 5 correspond to citations from the literature, e.g. WMO, 2021 or Lickley et al, 2022. The manuscript does not include any figures or tables. In order for the manuscript to better fit in the scope of ACP and be published in the journal, I suggest that the authors provide their own quantitative estimates of the various proposed options and/or their assessment of what would be the best options for the ozone depletion and for climate change issues.
Minor comments
Page 2, line 35. The authors could elaborate on the environmentally superior replacements of HFCs
Page 2, line 38. Tt seems that 1890 is a typo.
Page 2, line 44. cite also Young et al., 2021
Page 3, line 85. It seems that additional CFC-12 emission was not detected during the unexpected CFC-11 emission period in 2012 – 2018. Can the authors elaborate on that?
Page 4, line 96. Are the mentioned experimental and analytical use controlled by the Montreal Protocol or exempted?
Page 4, line 106. The sentence starting with “Where entirely used as feedstock” is not clear. For which use is CFC-113 production exempted? The whole paragraph on CFC-113 needs to be clarified.
Page 5, line 143-146. We miss information for fully understand the statement. A formula could help explain on shorter time intervals the offset could be smaller or larger than the adverse impact being offset.
Page 5, line 149-150. The authors only cite the literature. Evaluating health effects in other countries and latitudes warrants a whole new study.
Page 6, line 164. The end of the sentence is rather obscure. Global Warming Potentials are generally based on a 100 year time frame.
Page 7-8, line 204 – 2017. As mentioned in the introduction of this review, a quantitative estimate of the impact of each proposed action on ozone depletion and climate change is lacking.
References:
Lickley, M. J., Daniel, J. S., Fleming, E. L., Reimann, S., and Solomon, S.: Bayesian assessment of chlorofluorocarbon (CFC),
hydrochlorofluorocarbon (HCFC) and halon banks suggest large reservoirs still present in old equipment, Atmospheric Chem. Phys., 22, 11125–11136, https://doi.org/10.5194/acp-22-11125-2022, 2022Young, P. J., Harper, A. B., Huntingford, C., Paul, N. D., Morgenstern, O., Newman, P. A., Oman, L. D., Madronich, S., and Garcia, R. R.: The Montreal Protocol protects the terrestrial carbon sink, Nature, 596, 384–388, https://doi.org/10.1038/s41586-021-03737-3, 2021.
WMO: Report on the Unexpected Emissions of CFC-11: A Report of the Scientific Assessment Panel of the Montreal Protocol on Substances that Deplete the Ozone Layer, Geneva, Switzerland, 2021
Citation: https://doi.org/10.5194/acp-2023-53-RC1
Gabrielle B. Dreyfus et al.
Gabrielle B. Dreyfus et al.
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