The Impact of Continuing CFC‐11 Emissions on Stratospheric Ozone

Trichlorofluoromethane (CFC‐11, CFCl3) is a major anthropogenic ozone‐depleting substance and greenhouse gas, and its production and consumption are controlled under the Montreal Protocol. However, recent studies show that CFC‐11 emissions have been near constant or increasing since 2002. In this study, we use a two‐dimensional chemistry‐climate model to investigate the stratospheric ozone response to a range of future CFC‐11 emissions scenarios. A scenario with future emissions sustained at 10 gigagrams per year (Gg/year) above the baseline WMO (2018) A1 scenario results in minor additional global (90°S–90°N) ozone depletion of 0.13% by 2100, and a 1.5‐year delay in the global ozone recovery to 1980 levels, relative to the baseline. A scenario with 72.5 Gg/year (the 2013–2016 average) sustained to 2100 results in a substantial 15% increase in effective equivalent stratospheric chlorine and nearly 1% additional global ozone depletion by 2100, with a 7.5‐year delay in the recovery to 1980 global ozone levels, relative to the baseline. The ozone response averaged over time has a strong linear dependence on the cumulative amount of future CFC‐11 emissions under a wide range of scenarios. The resulting ozone response sensitivity gives a simple metric relating the time‐averaged ozone change to the cumulative CFC‐11 emissions. This sensitivity has an inverse dependence on future greenhouse gas concentrations (CO2, CH4, and N2O). For the medium Intergovernmental Panel on Climate Change Representative Concentration Pathway‐6.0 scenario, the sensitivity per 1,000 Gg of cumulative CFC‐11 emissions is −0.1% and −1% for global and Antarctic spring ozone, respectively. Plain Language Summary Stratospheric ozone protects the Earth's biosphere from harmful ultraviolet radiation and is key in determining the radiative balance of the atmosphere. CFC‐11 is a man‐made chlorofluorocarbon, and its emissions and subsequent break down in the stratosphere result in ozone depletion. Because of this, production and consumption of CFC‐11 have been controlled under the Montreal Protocol, resulting in a rapid decline in emissions starting in the late 1980s. Recent studies show that CFC‐11 emissions have increased in recent years, at odds with expected declines caused by the Montreal Protocol controls. In this study, we examine how potential future CFC‐11 emissions will impact stratospheric ozone. The ozone response is proportional to the amount of CFC‐11 emitted, and the response is substantial for a future projection in which the increased emissions during 2013–2016 continue to 2100. This scenario will postpone the return of global ozone to 1980 levels from mid‐2052 to 2060 and causes additional 1% global ozone depletion by 2100, compared to the baseline. Although there is uncertainty in projecting future emissions, the ozone response is strongly dependent on the amount of CFC‐11 emissions accumulated over time, allowing for a simple metric relating the ozone depletion to the cumulative amount of emissions.