The impact of continuing emissions of CFC-11 on the stratospheric ozone layer

Chlorofluorocarbons (CFCs) are both powerful ozone depleting substances and greenhouse gases. One of the most abundant CFCs is trichlorofluoromethane (CFC- 11). Its production and consumption has been controlled under the Montreal Protocol, resulting in a rapid decline in emissions starting in the late 1980s. As a result of this emissions decrease and the 52-year lifetime, tropospheric concentrations of CFC-11 peaked in about 1994, and have since been declining up to the present. However, Montzka et al. [2018] recently showed that CFC-11 emissions have increased over the last few years (2013-2016). This emissions increase cannot be explained by release from existing CFC-11 banks and is most likely associated with new production and consumption from East Asia. It is important to understand and quantify the stratospheric ozone response to potential future CFC-11 emissions increases.

In this study, we use the GSFC 2D and 3D models to investigate the effective equivalent stratospheric chlorine (EESC) and stratospheric ozone responses to a range of future CFC-11 emissions scenarios over the 2020-2100 time period. The largest ozone depletion occurs in the Antarctic lower stratosphere and global upper stratosphere, consistent with the expected response to chlorine perturbations. We examine the relationship between the amount of CFC-11 emissions and the magnitude of the ozone response. For global total column ozone, the response has a strong linear dependence on the cumulative amount of global CFC-11 emissions under a wide range of scenarios. This allows for a relatively simple diagnostic that can be used to estimate the ozone loss that would be expected for a given level of CFC-11 emissions. For 2020-2060, global total ozone decreases by 0.6 DU (0.2%) per 1000 Gg of cumulative CFC-11 emissions.