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Assessment for Decision-Makers Scientific Assessment of Ozone Depletion: 2014

Assessment for Decision-Makers: Scientific Assessment of Ozone Depletion: 2014, World Meteorological  Organization, Global Ozone Research and Monitoring Project—Report No. 56, Geneva, Switzerland, 2014.

• “The sum of the measured tropospheric abundances of substances controlled under the Montreal Protocol continues to decrease. Most of the major controlled ODSs are decreasing largely as projected, and hydrochlorofluorocarbons (HCFCs) and halon-1301 are still increasing. Unknown or unreported sources of carbon tetrachloride are needed to explain its abundance.
• Measured stratospheric abundances of chlorine- and bromine-containing substances originating from the degradation of ODSs are decreasing. By 2012, combined chlorine and bromine levels (as estimated by Equivalent Effective Stratospheric Chlorine, EESC) had declined by about 10–15% from the peak values of ten to fifteen years ago. Decreases in atmospheric abundances of methyl chloroform (CH3CCl3), methyl bromide (CH3Br), and chlorofluorocarbons (CFCs) contributed approximately equally to these reductions.
• Total column ozone declined over most of the globe during the 1980s and early 1990s (by about 2.5% averaged over 60°S to 60°N). It has remained relatively unchanged since 2000, with indications of a small increase in total column ozone in recent years, as expected. In the upper stratosphere there is a clear recent ozone increase, which climate models suggest can be explained by comparable contributions from declining ODS abundances and upper stratospheric cooling caused by carbon dioxide increases.
• The Antarctic ozone hole continues to occur each spring, as expected for the current ODS abundances. The Arctic stratosphere in winter/spring 2011 was particularly cold, which led to large ozone depletion as expected under these conditions.
• Total column ozone will recover toward the 1980 benchmark levels over most of the globeunder full compliance with the Montreal Protocol. This recovery is expected to occur before midcentury in midlatitudes and the Arctic, and somewhat later for the Antarctic ozone hole.”

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