Atmosphere Theme Report
Australia State of the Environment Report 2001 (Theme Report)
Lead Author: Dr Peter Manins, Environmental Consulting and Research Unit, CSIRO Atmospheric Research, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06746 9
Stratospheric Ozone (continued)
Ozone-depleting substances in the atmosphere [A Indicator 2.1]
The major ozone-depleting substances in the atmosphere are CFCs, methyl chloroform, carbon tetrachloride, halons and methyl bromide. CFCs were used in refrigeration, foam plastics, aerosol products and as solvents; halons as fire-fighting chemicals; methyl chloroform as a cleaning solvent; carbon tetrachloride as a cleaning solvent and in the manufacture of CFCs; and methyl bromide as an agricultural and building fumigant. HCFCs are minor ozone-depleting substances that are used as interim replacements for CFCs, largely as refrigerants. Global consumption of these ozone-depleting substances is controlled by the Montreal Protocol on Substances that Deplete the Ozone Layer (UNEP 1996). Australia is a signatory to (1988), and has ratified (1989), the Protocol and its amendments (in 1992 and 1994).
Atmospheric observations of ozone-depleting substances in the Southern Hemisphere have been made from 1978 to 2000 at Cape Grim, north-west Tasmania and elsewhere. Figure 69 shows atmospheric concentrations of CFCs, methyl chloroform, carbon tetrachloride, halons, methyl bromide and HCFCs. The data are selected to represent large-scale, unpolluted air masses in the Southern Hemisphere and thus the long-term records reflect global changes in the emissions of these ozone-depleting substances. Their concentrations can be expressed as 'equivalent effective stratospheric chlorine', or more simply 'stratospheric chlorine', which is a way of representing their ability to destroy stratospheric ozone. The stratospheric chlorine observations are compared with scenarios developed for the most recent international scientific assessment of ozone depletion (WMO 1999). The comparison assumes global compliance to the Montreal Protocol, with consumption of ozone-depleting substances in the developed world largely phased out in the 1990s and in the developing world, consumption largely phased out by 2010.
Figure 69: Stratospheric chlorine (ppb) from the major ozone-depleting substances: CFCs, chlorinated solvents (methyl chloroform, carbon tetrachloride), halons, methyl bromide and HCFCs.
Data are based on in situ observations at Cape Grim, Tas., and measurements on the Cape Grim air archive (1978-2000), compared to scenario A3 (Madronich & Velders 1999) assuming global compliance to the Montreal Protocol (top). Location of Cape Grim, Tas. (bottom).
Source: CSIRO; Cape Grim Baseline Air Pollution Station; Oram et al. (1995); Fraser et al. (1999); Madronich & Velders (1999); Prinn et al. (2000)
Ozone-depleting substances that continue to grow in the background atmosphere are several of the CFCs and halons and all of the HCFCs, because they continue to be emitted from their large 'banks' in the developed world and because of expanding use in the developing world. The chlorinated solvents (methyl chloroform and carbon tetrachloride) are in decline and methyl bromide levels are constant. The net stratospheric chlorine data show (Figure 69) that the accumulation of ozone-depleting substances in the background atmosphere slowed during the early 1990s, stopped in the mid-1990s (maximum in 1994) and now is declining slowly. This is a significant development since 1996 (SoE 1996), which showed a slight reduction of total chlorine in the lower atmosphere in the early 1990s. Models indicate that stratospheric chlorine and ozone responses lag chlorine behaviour in the lower atmosphere by about three to five years, suggesting that stratospheric ozone depletion over Australia and Antarctica should have peaked in the late 1990s.
Ozone depletion was first observed in Antarctica in the early 1970s (first reported by Farman et al. 1985) when stratospheric chlorine levels had risen to about 2 ppb (Figure 70). Predictions of future chlorine levels suggest that ozone recovery is expected by about 2050 (when chlorine levels fall to about 2 ppb). However, recovery may be delayed by as much as 50 years because of climate change (a colder stratosphere, resulting from enhanced levels of greenhouse gases, leads to more ozone destruction in polar regions) and larger than anticipated use of ozone-depleting substances, in particular CFCs and halons, in developing countries. Illegal production of ozone-depleting substances is believed to be relatively small and is not expected to delay ozone recovery significantly (Fraser 2000).
Future emissions are calculated assuming global compliance to the Montreal Protocol (scenario A3, Madronich & Velders 1999). The contribution of methyl bromide is split into anthropogenic (A) and natural (N) components and the natural ozone-depleting substance methyl chloride is included. The line at 2 ppb corresponds to when ozone depletion was first detected (about 1980) and when ozone recovery is anticipated (about 2050). Other chlorocarbons such as chloroform (CHCl3), dichloromethane (CH2Cl2) and a range of chlorinated solvents contribute a further 0.1 ppb to stratospheric chlorine (not shown).
Source: Madronich and Velders (1999).
Implications
Ozone recovery is expected by about 2050 but may be delayed by as much as 50 years.