Modelling the Potential Impacts on Total Column Ozone Recovery of the Recent, Unexpected Increases in CFC-11 emissions

The Montreal Protocol was agreed as a response to the unambiguous detection of ozone depletion driven by halogen compounds, and is regarded as the most successful environmental treaty to date. However, recent observations indicate that compliance with the Protocol may not be complete, with studies identifying a new source of CFC-11 in East Asia. Any increase in the emissions of CFC-11 will have an impact on the timing of ozone recovery, depending on their duration and magnitude.

Using the UM-UKCA model, the immediate and future impacts of recent emissions of CFC-11 are explored. A baseline scenario following the WMO2014 recommendations for lower boundary CFC mixing ratios is performed, from which separate integrations are initialised in 2012 and run to 2100 following different scenarios for CFC-11 (and CFC-12) emissions. A range of assumptions are made about the magnitude and duration of the additional CFC production, their direct emissions into the atmosphere and the effect on the banks. Using these scenarios, potential future changes to stratospheric chlorine loading and total column ozone values are examined in order to determine the impact on the timing of ozone recovery if rapid action is not taken to curb these recent emissions. The relationship between cumulative CFC emissions and the timing of ozone recovery is explored in order to develop scenario independent conclusions which can be used to establish the impact of future CFC emissions pathways on ozone recovery in the real world.