SAP Rising
and the ozone news is good ...
A strength of the Montreal Protocol on Protection of the Ozone Layer is the ongoing requirement to report back to the Signatory Parties with updated Assessments of our understanding from three separate panels: the Atmospheric Science Assessment Panel, the Alternative Chemicals Assessment Panel, and the Environmental Effects Assessment Panel. In each case including any interactions with Climate Change. Updates are required every four years. The executive summary of the 2022 Science Assessment Panel (SAP) has just been released and can be found here.
The good news story is nicely summarised in their very first figure, reproduced below.
The figure shows timelines from 1960 - before the problem emerged - with measurements up the current time and model predictions continuing on to the end of the current century of:
a) Emissions of ozone-depleting substances (expressed as CFC-11-equivalent emissions),
b) Atmospheric concentrations of equivalent effective chlorine (EECl),
c) Global total ozone, and
d) October Antarctic total ozone.
Together they show that measurements and models are in good agreement; and that we’re past the worst and on a path to recovery (or perhaps even a ‘super-recovery’).
More details below for the unsatiated …
Annual CFC-11-equivalent emissions are computed for the ozone-depleting-substances (ODSs) shown in the legend by multiplying mass emissions of each substance by its ozone depletion potential (ODP) (panel a). Historical emissions are derived from the measured atmospheric abundances of individual ODSs. Future projections of emissions assume full compliance with the Montreal Protocol.
The annual abundances of “equivalent effective chlorine” (EECl), shown for the global surface, are based on surface abundances (measured or derived from projected emissions and lifetimes) of the chlorine- and bromine-containing substances (panel b). The bromine abundances are weighted by a factor of 65 to account for their greater efficiency in ozone destruction. The white line with an arrow marks when EECl returns to its 1980 value.
Global total column ozone represents an annual average over latitudes 60°N to 60°S (panel c) and Antarctic total column ozone represents an October average over latitudes 70°S to 90°S (panel d). Panels (c) and (d) include comparisons with chemistry-climate model results (black lines with grey shadings indicating uncertainty ranges) and available observations (purple lines). The chemistry-climate model projections assume compliance with the Montreal Protocol and an increase in greenhouse gases following either a low climate forcing scenario (blue), a medium climate forcing scenario (orange), or a high climate forcing scenario (red).
The full SAP report should be available around year’s end. I was most heavily involved with the Twenty Questions and Answers section, and am planning to report on specific aspects over the next few months.