Continuing industrial emissions are delaying the recovery of the stratospheric ozone layer

The Montreal Protocol on Substances that Deplete the Ozone Layer has greatly restricted the global production and consumption of long-lived ozone-depleting substances (ODS). However, ODS used or consumed as feedstocks in the manufacture of other chemicals are excluded from restrictions. This exclusion was based on the assumption that emission rates of feedstocks were only 0.5% of the amount produced and that feedstock production would decline in the future, with remaining emissions too small to significantly affect the stratospheric ozone or its recovery. In sharp contrast, feedstock emissions are now assessed as being substantially higher (typically 3.6% of production), and feedstock production and use has been rising rather than falling. Here, scenarios in which feedstock-related ODS emissions continue at this current fraction of production, rather than the 0.5% reference case, are projected until 2100. Without additional measures, these elevated emissions could delay the recovery of the mid-latitude stratospheric ozone layer by 7 (6 - 11) years. Furthermore, limiting ODS feedstock emissions would also reduce their effect on direct radiative forcing and on climate change.