Abstract
Abstract. The rates at which ozone-depleting substances (ODSs) are removed from the atmosphere, which determine the lifetimes of these ODSs, are key factors for determining the rate of ozone layer recovery in the coming decades. We present here a comprehensive uncertainty analysis of future mixing ratios of ODSs, levels of equivalent effective stratospheric chlorine (EESC), ozone depletion potentials, and global warming potentials (GWPs), using, among other information, the 2013 WCRP/SPARC (World Climate Research Programme/Stratospheric Processes and their Role in Climate) assessment of lifetimes of ODSs and their uncertainties. The year EESC returns to pre-1980 levels, a metric commonly used to indicate a level of recovery from ODS-induced ozone depletion, is 2048 for midlatitudes and 2075 for Antarctic conditions based on the lifetimes from the SPARC assessment, which is about 2 and 4 yr, respectively, later than based on the lifetimes from the WMO (World Meteorological Organization) assessment of 2011. However, the uncertainty in this return to 1980 levels is much larger than the shift due to this change in lifetimes. The year EESC returns to pre-1980 levels ranges from 2039 to 2064 (95% confidence interval) for midlatitudes and from 2061 to 2105 for the Antarctic spring. The primary contribution to these ranges comes from the uncertainty in the lifetimes, with smaller contributions from uncertainties in other modeled parameters. The earlier years of the return estimates derived by the uncertainty analysis, i.e., 2039 for midlatitudes and 2061 for Antarctic spring, are comparable to a hypothetical scenario in which emissions of ODSs cease in 2014. The later end of the range, i.e., 2064 for midlatitudes and 2105 for Antarctic spring, can also be obtained by a scenario with an additional emission of about 7 Mt CFC-11 eq. (eq. – equivalent) in 2015, which is the same as about 2 times the projected cumulative anthropogenic emissions of all ODSs from 2014 to 2050, or about 12 times the projected cumulative HCFC emissions from 2014 to 2050.
Highlights
Projections of the mixing ratios of ozone-depleting substances (ODSs) and the levels of chlorine and bromine in the stratosphere require knowledge of future production and loss processes in addition to current atmospheric abundances and amounts of ODSs present in existing equipment
Through a comprehensive uncertainty analysis, that the uncertainty in the lifetimes of the ODSs is the dominant term in the overall uncertainty in total effective stratospheric chlorine (EESC) levels
The year EESC returns to pre-1980 levels is 2048 for midlatitude conditions and 2075 for Antarctic conditions, based on our baseline for ODS emissions and lifetimes from the Stratospheric Processes And their Role in Climate (SPARC) (2013)
Summary
Projections of the mixing ratios of ozone-depleting substances (ODSs) and the levels of chlorine and bromine in the stratosphere require knowledge of future production and loss processes in addition to current atmospheric abundances and amounts of ODSs present in existing equipment. The new lifetimes and associated uncertainties and their effects on future EESC levels are the basis of the analysis presented here. The effects of the new SPARC (2013) lifetimes on future mixing ratios of ODSs and EESC levels are evaluated by comparing these values with those calculated using the lifetimes from WMO (2011). We recognize that other factors are important for the future development of the ozone layer, such as future concentrations of nitrous oxide (N2O), methane (CH4), very short-lived halogen containing species, and changes in temperature and circulation in the atmosphere These other factors are not considered here. 2. The results of the box model calculations and the effects of the uncertainties in the lifetimes and other parameters on mixing ratios and EESC are presented in Sect.
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