Qualitative Evidence for Ozone Recovery

Figures 1 and 2 show some qualititative evidence that ozone IS following the provisions of the Montreal Protocol.

In Figure 1, 3D chemical transport model (CTM) simulations of the total column ozone amount averaged between the latitudes of 60° south and 60° north are shown in red. The CTM simulations, made in 2005, were forced by time-dependent inputs of the concentrations of chlorine source gases, 11-year cyclic variations of solar ultraviolet radiation and time-varying aerosol surface area densities representing the El Chichón and Pinatubo volcanic eruptions. These model calculations were reported in Stolarski et al. [2006]. In Figure 1 the measurements used for comparison to the model projection run from late 1978 to 2004 from Stolarski and Frith [2006]. These were the data available at the time of the publication of the model results by Stolarski et al. [2006]. Note that the measurements generally follow the downward trend in total column amount of ozone with an 11-year solar cycle that is consistent with the model results. Closer inspection reveals that the measurements from the late 1970's to the early 1990's are somewhat below the model results, while the measurements from the early 1990's into the 2000's are about equal to the model results. In other words, this particular model computation indicated somewhat stronger downward trends than appeared in the measurements.

Figure 1: CTM projections of quasi-global (60°S-60°N) total column ozone made in 2005 (thick red line with range of seasonal variation indicated by red shaded area). Blue line indicates monthly measurements by SBUV series of satellites available at the time of the model computations.

Figure 2 shows the same model results with extended measurements described in Frith et al. [2014]. These measurements have been extended into 2017 as described on the Merged Ozone Data (MOD) web page. The measurements appear to continue to qualitatively agree with the model project 12 years after that projection was made. The original model projection assumed a peak ultraviolet radiation for solar cycle 24 shortly after the year 2010 that was the same as that for the previous two cycles. The actual solar cycle 24 was significantly weaker as reflected in the ozone measurements of Figure 2.

Figure 2: CTM projections of quasi-global (60°S-60°N) total column ozone made in 2005 (thick red line with range of seasonal variation indicated by red shaded area). Blue line indicates monthly measurements by SBUV series of satellites updated into 2017.