Stratospheric Ozone Recovery in Light of the Slowdown in the Decline of CFC-11

The recent unexpected slowdown in the decline of CFC-11 atmospheric concentrations will result in modifications to projections of future Equivalent Effective Stratospheric Chlorine (EESC) and the recovery of stratospheric ozone. This slowdown suggests significant new production of CFC-11 after 2010, the year when its global production was banned for dispersive uses by the Montreal Protocol. The significance of any delay in ozone recovery depends on how long the apparent illegal production of CFC-11 continues and how much of the recently produced CFC-11 has been emitted directly to the atmosphere versus stored in the bank in the form of insulating foams, for example. In this study we first update the observationally-derived CFC-11 emission time series based on updated measurements and estimates of the influence of interannual stratosphere-troposphere transport variability on measured surface concentrations of CFC-11. We then estimate the enhancement of CFC-11 emissions above those that were expected based on the timing of the Montreal Protocol phase-out of CFC-11 production. Based on the emission enhancements, derived from both what have already occurred as well as from a range of future scenarios considering different assumptions about post-2010 CFC-11 production, we estimate the effects on the recent and projected EESC time series and subsequent delay in stratospheric ozone recovery.