The Recent Slowdown in the Decline of CFC-11: New Emissions, Stratospheric Loss Variability, or Both?

The global growth rate and hemispheric gradient of CFC-11 has changed unexpectedly since 2013 following a decade of near constant values. We use surface measurements of CFC-11 and other long-lived tracers, box models and a global chemistry-climate model to investigate the changes. Our analysis suggests the possibility that new CFC-11 emissions may be necessary to explain the recent changes. We have also found that interannual variability in the transport of stratospheric loss to the troposphere substantially contributes to recent changes in CFC-11 and other trace gases that are destroyed in the stratosphere. We show that interannual variability in stratospheric transport can be aliased into the emission estimates of a number of long-lived trace gases. This aliasing of the emission estimates can affect predictions of future abundances of trace gases important to stratospheric ozone recovery as well as climate.