Stratospheric ozone


On the basis of the extent of international sign-on and results achieved, the Montreal Protocol is one of the world’s most effective international environment protection agreements. Various ‘world-avoided’ studies have demonstrated the importance of measures implemented under the protocol, not only in avoiding further damage to the ozone layer and allowing its gradual recovery, but also in significantly reducing the extent of climate change in coming decades. This is particularly important at high latitudes, where the avoided ozone depletion would have had a large effect on surface climate.104,169

Based on analysis of historical ODS emissions and potential emission scenarios, Velders et al.170 reach a similar conclusion, noting that ‘the climate protection already achieved by the Montreal Protocol alone is far larger than the reduction target of the first commitment period of the Kyoto Protocol’. Additional climate change mitigation could be achieved under the Montreal Protocol through management of substitute fluorocarbon gas emissions and by mandating gases with low global warming potentials as alternatives.

Other world-avoided studies have modelled decreases in ozone levels and resulting increases in ground surface solar UV radiation levels. The excess radiation would have had major adverse effects on terrestrial and aquatic ecosystems and on human health. For example, mid-latitude ozone losses in the Northern Hemisphere would have reduced the time taken to sunburn (under a clear sky at noon) from 15 to 5 minutes. The amount of DNA-damaging UV reaching Earth would have increased between 1980 and 2065 by 550%.171

Since its establishment in 1987, controls under the protocol have been progressively expanded to cover a broad range of ODSs (including some of the first generation of CFC substitutes) and to accelerate initial phase-out timetables. Table 3.9 summarises the present control measures.

Table 3.9 Summary of Montreal Protocol measures
Ozone depleting substance Developed countries Developing countries
Chlorofluorocarbons Phased out end of 1995a Total phase-out by 2010
Halons Phased out end of 1993 Total phase-out by 2010
Carbon tetrachloride Phased out end of 1995a Total phase-out by 2010
Methyl chloroform Phased out end of 1995a Total phase-out by 2015
Hydrochlorofluorocarbons Freeze from beginning of 1996b
35% reduction by 2004
75% reduction by 2010
90% reduction by 2015
Total phase-out by 2020c
Freeze in 2013 at a base level calculated as the average of 2009 and 2010 consumption levels
10% reduction by 2015
35% reduction by 2020
67.5% reduction by 2025
Total phase-out by 2030d
Hydrobromofluorocarbons Phased out end of 1995 Phased out end of 1995
Methyl bromide
(horticultural uses)
Freeze in 1995 at 1991 base levele
25% reduction by 1999
50% reduction by 2001
70% reduction by 2003
Total phase-out by 2005
Freeze in 2002 at average 1995–98 base levele
20% reduction by 2005
Total phase-out by 2015
Bromochloromethane Phase-out by 2002 Phase-out by 2002

a With the exception of a very small number of internationally agreed essential uses that are considered critical to human health and/or laboratory and analytical procedures

b Based on 1989 hydrochlorofluorocarbon (HCFC) consumption with an extra allowance (ozone depletion potential weighted) equal to 2.8% of 1989 chlorofluorocarbon consumption

c Up to 0.5% of base-level consumption can be used until 2030 for servicing existing equipment, subject to review in 2015

d Up to 2.5% of base-level consumption can be used until 2040 for servicing existing equipment, subject to review in 2025

e All reductions include an exemption for preshipment and quarantine uses

The timetable set by the Montreal Protocol applies to bulk consumption of ozone depleting substances (ODSs). Consumption is defined as the quantities manufactured plus imported, less those quantities exported in any given year. Percentage reductions relate to the designated ‘base year’ for the substance. The protocol does not forbid use of existing or recycled controlled substances beyond the phase-out dates.
Further information on these ODSs can be seen in the United Nations Environment Programme Ozone Secretariat’s Handbook for the international treaties for the protection of the ozone layer (see Section 1.2 of the handbook for links to graphs displaying ODS phase-out timetables).
For Australia’s accelerated HCFC phase-out timetable, see Part IV of the Ozone Protection and Synthetic Greenhouse Gas Management Act 1989.

Source: Australian Government Department of Sustainability, Environment, Water, Population and Communities172

Australia was an early supporter of international efforts to protect the ozone layer and has ratified the Montreal Protocol and all subsequent amendments. It moved quickly to give legislative effect to its obligations under the protocol, establishing the Ozone Protection and Synthetic Greenhouse Gas Management Act 1989. Australia’s reduction in the use of substances controlled under the protocol (all of which are imported) has been well ahead of its international obligations (Figure 3.32). For example, Australia will essentially phase-out use of hydrochlorofluorocarbons four years ahead of 2020, the date scheduled under the protocol.107

Figure 3.32

Source: Australian Government Department of Sustainability, Environment, Water, Population and Communities172

Figure 3.32 Australia’s performance against Montreal Protocol obligations for controlled ozone depleting substance imports

(2011). Ambient air quality: Stratospheric ozone. In: Australia state of the environment 2011, Australian Government Department of the Environment and Energy, Canberra,, DOI 10.4226/94/58b65c70bc372