3.1 Stratospheric ozone depletion
Ozone hole stabilised but increased exposure to UV-B radiation will persist
About 90% of ozone resides in a layer of the upper atmosphere called the 'stratosphere'. This stratospheric ozone layer protects the earth from all but a small fraction of the ultraviolet radiation from the sun. Human use of certain chemicals has significantly depleted stratospheric ozone concentrations leading to what is commonly referred to as the ozone 'hole'. As the stratospheric ozone layer is depleted, the intensity of radiation on earth increases, leading to potentially harmful effects on humans, animals, plants and air quality.
Although the depletion of the ozone layer has reached record levels, scientific evidence confirms the success of Montreal Protocol strategies which require parties to phase out the use of ozone-depleting substances. Concentrations of these chemicals in the lower atmosphere have fallen and this is now being translated into similar reductions in concentrations in the stratosphere. As a result, a recovery of the ozone layer is expected in the next two decades, with full restoration within the next 50–100 years.
Status of Indicator
3.1 Concentration of ozone-depleting substances in the atmosphere
Concentrations of ozone-depleting substances are decreasing.
3.2 Stratospheric ozone concentrations
Levels have generally stabilised since catastrophic falls in the 1980s.
3.3 Recovery and destruction of ozone-depleting substances
Recovery and destruction of ozone-depleting substances is continuing at an increasing rate, resulting in a decline in their use.
3.4 Level of UV-B radiation at the surface
Estimated to be at higher than normal levels, consistent with ozone layer depletion.
Importance of the issue
All life on earth is protected from the damaging ultraviolet radiation of the sun by a thin shield of ozone gas in the stratosphere, 20–50 kilometres above the planet. Ozone is an extremely rare component of the earth's atmosphere, making up only three out of every 10 million molecules of air.
When some substances with a high degree of stability are released at ground level, they can persist long enough to travel up into the stratosphere. Examples include halocarbons and carbon compounds containing chlorine or bromine. These compounds are broken down in the stratosphere under the influence of ultraviolet (UV) radiation. Through a series of reactions, the chlorine and bromine atoms produced act as catalysts for reactions which destroy ozone molecules. This accelerated destruction of ozone in the stratosphere upsets the natural balance of ozone production and destruction. For example, each chlorine atom can destroy an estimated 100,000 ozone molecules before it is removed from the stratosphere. Bromine is even more effective at destroying ozone molecules, although it is present in smaller quantities than chlorine.
These ozone-destroying reactions are particularly intense during the springtime melting of the stratospheric ice clouds that form above Antarctica in the cold Southern Hemisphere winter. The result is a 'hole' in the ozone layer, an area of sharp decline in ozone concentrations over most of Antarctica for two or three months during the Southern Hemisphere spring. A similar, but lesser, pattern emerges over the Arctic in the Northern Hemisphere spring.
Currently the ozone layer above the whole of Antarctica thins to between 40 and 55% of its pre-1980 levels with up to a 70% deficiency for short periods (Figure 3.1). At some altitudes ozone destruction is almost total. In the spring of 2000 the hole in the ozone layer over Antarctica grew at an unprecedented rate and reached a record depth (UNEP 2000). In 2002 the hole was much smaller than in the preceding two years, although this variation has been attributed to natural changes in the meteorological conditions in the stratosphere (WMO 2003).
Figure 3.1: October ozone levels over Antarctica since the late 1950s
Source: British Antarctic Survey data, as at 2000
Any reduction in ozone concentrations in the stratosphere means less UV radiation is absorbed and more reaches the earth's surface. Australia experiences extreme levels of solar UV radiation because of its location in the middle and low latitudes of the Southern Hemisphere and its relatively clean and cloudless skies.
Higher levels of exposure to UV radiation, particularly UV-B radiation, can have potentially harmful effects on human and animal health, plants, microorganisms and air quality. In humans, exposure to UV-B is associated with eye damage, sunburn, skin cancers and cataracts. Stratospheric ozone depletion over mid-latitudes means that UV-B levels in major population areas of southern Australia are likely to have risen by 10–15% over the past 20 years. This increase could translate to a greater than 15% increase in skin cancers if sunscreens and covers are not applied. Recent Cancer Council NSW projections indicate that the incidence of melanoma is expected to rise across NSW between 2001 and 2010 (Tracey & Supramanium 2002). Melanoma incidence rates are directly related to UV-B exposure.
Animals suffer similar effects to humans from higher UV-B levels. Aquatic fauna, such as frogs, and aquatic flora, such as phytoplankton, are particularly vulnerable to UV-B radiation. Recent studies of the effects of UV-B on phytoplankton have confirmed adverse effects on growth, photosynthesis, protein and pigment content, and reproduction (UNEP 2000). At high levels, UV-B radiation also affects plant photosynthesis processes, which may reduce growth and harm crop yields and quality.
As stratospheric ozone is reduced and UV-B radiation increases, there is also an interaction with other sources of pollution, causing environmental change. Increases in UV-B have a potential impact on air quality at lower levels of the atmosphere. The nature of these impacts is uncertain, although they may increase production of some pollutants such as photochemical smog but reduce others by increasing their rates of removal from the atmosphere.
Response to the issue
The main government responses to the decline in stratospheric ozone have been to phase out the production and use of major ozone-depleting substances (except for essential uses) and facilitate the collection and storage or destruction of some of these substances. The responses have been part of meeting international commitments covered by the Montreal Protocol on Substances that Deplete the Ozone Layer.
The Montreal Protocol was signed in 1987 and set mandatory targets for phasing out the production and consumption of major ozone-depleting substances such as chlorofluorocarbons (CFCs) and halocarbons. On a global basis the Protocol resulted in a reduction in the total production of CFCs. By the end of 1998 production of the original controlled CFCs had fallen by 95% in industrialised countries (UNEP 2000). Production of the most damaging ozone-depleting substances in developed countries has now been eliminated, except for a few critical uses, and by 2010 will also be eliminated in developing nations. Improved scientific knowledge and an understanding of the problem of ozone-depleting substances have seen phase-out dates brought forward in developed countries.
Australia's obligations under the Montreal Protocol have been implemented at the Commonwealth level, with complementary State and Territory legislation. Commonwealth ozone legislation and the NSW Ozone Protection Act 1989 and subsequent regulations placed controls on the use of ozone-depleting substances. As a result of these measures, the production and import of CFCs and halocarbons has been banned in NSW. Recycled CFCs may be used in existing equipment while still available, subject to emission controls, and some essential uses of halocarbons are permitted in essential aviation, defence and maritime applications. Hydrochlorofluorocarbons (HCFCs) will be phased out in Australia from 2016 and at the international level from 2030.
As part of meeting its international commitments under the Montreal Protocol, the Commonwealth Government established the National Halon Bank to collect and store halocarbons as industry and government decommissioned them from non-essential uses. Since 1993 over 1200 tonnes of excess halon 1211 has been destroyed in Australia. The bank holds 500 tonnes of reclaimed halon 1301, half to meet essential uses and half stored for the United States Government. It is estimated that 20 tonnes of halon 1211 and approximately 180 tonnes of halon 1301 remain installed in halocarbon-using equipment. Halon use is restricted to civil and military aviation fields, merchant shipping, and certain defence applications. The Australian Halon Management Strategy sets out future requirements relating to essential uses of these substances.
Effectiveness of responses
The high degree of stability of ozone-depleting substances makes them suitable for a wide range of industrial uses as refrigerants, in air-conditioning and firefighting, and as insulation and furniture foams. However it also means they will persist in the atmosphere for decades to come despite concerted international action to reduce and phase out their use. Although the exact rate of recovery is unknown, a restored global ozone layer will be due mainly to a decrease in the chlorine and bromine loads in the stratosphere. The ozone layer will be particularly vulnerable over the next decade even if there is full compliance with the Montreal Protocol. Continued production of ozone-depleting substances, at 1999 levels for example, would delay recovery of the ozone layer until well past 2100.
The quantity of ozone-depleting substances removed from the environment is a measure of the effectiveness of government strategies and industry action in preventing further releases of these substances and protecting the ozone layer. Figure 3.2 shows the total volume of ozone-depleting refrigerants recovered in Australia. It is estimated that NSW accounts for approximately 25% of the national total of refrigerants reclaimed.
Figure 3.2: Recovery of ozone-depleting refrigerants
Source: Refrigerant Reclaim Australia data, as at July 2002
Sales of CFCs have almost ceased. In all areas where CFCs and halocarbons were traditionally used, replacements with little or no ozone-depletion potential are now being used. In NSW, some CFCs remain in existing fixed refrigerators and air-conditioners and some insulation materials, but ongoing use is confined to very limited medical and scientific needs.
Measurements from the Cape Grim baseline air pollution station in north-western Tasmania and similar stations elsewhere around the globe are showing a decline in atmospheric concentrations of many ozone-depleting substances. Concentrations, expressed as total equivalent chlorine level, peaked at just under 4 parts per billion (ppb) in 1992–94. Monitoring shows that these are now slowly declining, together with decreases in concentrations of carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), the chlorofluorocarbons (CFC-11, CFC-12 and CFC-113) and the interim CFC alternative HCFC-22. The total tropospheric bromine from halons continues to increase at about 3% a year, or about two-thirds of the rate in 1996 (WMO/UNEP 2002).
The use of the most damaging ozone-depleting substances will be largely eliminated in Australia over the next two years. While the phase-out of less damaging ozone-depleting substances will continue over some decades, the major future gains in global ozone protection will be achieved through actions in developing and some other developed countries rather than Australia.
The complex interaction between ozone destruction and climate change, emphasises that environmental problems cannot be dealt with in isolation. Destruction of stratospheric ozone in recent years has led to a cooling of the lower stratosphere, masking, to some extent, the warming effects of increasing greenhouse gas emissions. At the same time increased ozone in the lower troposphere (where ozone becomes a pollutant) also contributes to the build-up of greenhouse gases and global warming.
The success of international, national and state efforts to reduce ozone-depleting substances in the atmosphere is regarded as a model for other international environment programs. Despite this there is still some scope for tightening the control schedules at an international level for the remaining ozone-depleting substances in order to hasten the recovery of the ozone layer.
The growth in the use of transition substances such as hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride in areas where CFCs and halocarbons were traditionally used (such as refrigeration, solvent cleaning and firefighting) is becoming an emerging issue. Agriculture sector efforts to phase out the use of methyl bromide for the fumigation of pests and weeds need to continue.
3.2 Climate change
3.3 Urban air quality
6.7 Aquatic species diversity