3.2 Stratospheric ozone depletion

Substantial recovery of the ozone layer is expected in the next two decades.

Although the depletion of the stratospheric ozone layer has reached record levels, monitoring confirms that the phasing-out of ozone-depleting substances and their use has led to falling concentrations of these chemicals, first in the lower atmosphere, and now in the stratosphere. As a result, substantial recovery of the ozone layer is expected in the next two decades, with full restoration within the next 50–100 years.

The long time lag between control and recovery means that stratospheric ozone depletion will continue to pose a risk to environmental and human health from ongoing exposure to elevated UV-B radiation.

In 2003, the Commonwealth Government extended its ozone-protection legislation to allow for the creation of a single national system for managing ozone-depleting substances and their synthetic replacements that act as greenhouse gases. The Regulations under this Act commenced in 2005 and 2006, replacing NSW's own ozone-protection legislation.

NSW indicators

Introduction

The ozone layer is a diffuse shield of gaseous ozone in the stratosphere, 20–50 kilometres above sea level, which helps protect the Earth from damaging levels of UV radiation from the sun.

Stratospheric ozone is destroyed by ozone-depleting substances, such as those containing the halogens chlorine, fluorine and bromine. Most of these compounds are industrial products or by-products and include chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, and methyl bromide. They are usually very unreactive compounds created for their effectiveness as refrigerants, fire suppressants and fumigants. Because they are unreactive, they persist in the atmosphere for decades as they travel upwards to the stratosphere. There, under the influence of UV radiation, they break down and release halogen atoms which act as catalysts for the reactions that destroy ozone molecules. Most ozone-depleting substances do not occur naturally, and their presence in the stratosphere upsets the natural balance of ozone production and destruction, greatly accelerating ozone destruction.

These ozone-destroying reactions affect the ozone layer globally, but are particularly intense during the springtime melting of the stratospheric ice clouds that form above Antarctica in the Southern Hemisphere winter. The result is a 'hole' in the ozone layer, an area of sharp decline in ozone concentration over most of Antarctica during the Southern Hemisphere spring. A similar, but lesser, pattern emerges over the Arctic in the Northern Hemisphere spring.

Current status and trends

The ozone layer above the whole of Antarctica now thins to between 40% and 55% of its pre-1980 levels, with up to a 70% deficiency for short periods (Figure 3.5). At some altitudes ozone destruction is almost total. Stratospheric ozone is believed to have reached its minimum level in recent years, with lower rates of depletion expected in future years as a result of the lower concentrations of ozone-depleting substances in the stratosphere.

Figure 3.5: Average October ozone levels over Antarctica since the mid-1950s

Source: British Antarctic Survey data 2005

Notes: The red line is a polynomial trendline demonstrating the trend in ozone levels over time.

Even though the Southern Hemisphere ozone hole is no longer increasing, its recurrence each year exposes Australians to increased UV radiation. Higher levels of exposure to UV radiation, particularly UV-B radiation, can have potentially harmful effects on human and animal health, plants, micro-organisms and air quality. In humans, exposure to UV-B is associated with eye damage and cataracts, sunburn and skin cancers. Melanoma incidence rates are directly related to UV-B exposure.

Any reduction in ozone concentrations in the stratosphere means less UV radiation is absorbed and more reaches the Earth's surface. 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. With relatively long data records, a clear correlation between declining ozone and rising UV radiation on clear-sky days has been seen at Lauder (South Island of New Zealand) (McKenzie et al. 1999; McKenzie et al. 2000). Similar trends are probably occurring over the area of south-eastern Australia. This increase could translate to a greater than 15% increase in skin cancers if sunscreens and covers are not applied. Although not definitively due to stratospheric ozone depletion, melanoma incidence has risen 15% in men and 12% in women over the past 10 years, and if this trend continues the Cancer Institute estimates that by 2011 there will be 4184 new cases of melanoma each year for NSW (Cancer Institute NSW 2005). 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). In crops, UV-B radiation at high levels may reduce growth and harm both crop yields and quality.

The depletion of stratospheric ozone and consequent increase in UV-B in the lower atmosphere also affects climate conditions and air quality at ground level. Reduced stratospheric ozone results in less absorption of solar energy and reduced temperatures in the stratosphere. This increases solar energy in the lower atmosphere, increasing temperature and contributing to climate change. As noted in Atmosphere 3.1 climate change exacerbates stratospheric ozone depletion. Additionally, UV-B radiation is necessary for forming ground-level ozone in the lower atmosphere (see Atmosphere 3.3).

Response to the issue

An international treaty, the Montreal Protocol on Substances that Deplete the Ozone Layer (the Montreal Protocol), was signed in 1987. The protocol set mandatory targets for phasing out the production and consumption of major ozone-depleting substances such as CFCs and halons by 1995 in developed countries and by 2010 in developing countries. The timetable has been under constant revision since 1987, with phase-out dates accelerated in accordance with scientific understanding and technological advances.

Australia's obligations under the Montreal Protocol have been implemented at the Commonwealth level, with complementary state and territory legislation for ozone protection gradually being replaced by Commonwealth legislation. Accordingly, the NSW Ozone Protection Regulation 1997 is scheduled to be repealed in late 2006.

Commonwealth ozone-protection regulations control the manufacture, import and export of all major ozone-depleting substances in Australia, and have resulted in their complete phasing out in Australia, with the exceptions of HCFCs, which will be essentially phased out by 2015, and methyl bromide used for quarantine and feedstock purposes, which is not currently controlled under the Montreal Protocol. The Commonwealth regulations allow for limited categories of essential or critical use for halons, CFCs and methyl bromide where no feasible alternatives are available. These essential or critical uses are approved by the international community through the Montreal Protocol and include applications in agriculture, medicine, aviation, defence and the maritime industry.

Transition substances, such as hydrofluorocarbons and perfluorocarbons (which were used in place of CFCs and halons as refrigerants, solvents, cleaning solutions and fire extinguishers), are strong greenhouse gases and contribute to climate change. Their concentrations are rising rapidly in the atmosphere (as shown by measurements at monitoring stations such as at Cape Grim), albeit from currently low concentrations. Australia is the first country to implement integrated control measures to manage both ozone-depleting substances and their synthetic replacements that can also act as greenhouse gases. Under these measures, the same import, export, production, and end-use controls apply to all ozone-depleting substances, including these transition substances.

The recovery of ozone-depleting substances from products that are already in use – for example, from old refrigerators and air conditioning units – is another important part of the response to stratospheric ozone depletion. Since 1993, Australia has collected more than 3000 tonnes of ozone-depleting substances which have either been recycled, stored or destroyed. Nonetheless, significant amounts remain to be collected.

Future directions

Australia's response to phasing out the use of ozone-depleting substances under the Montreal Protocol has been swift and effective. However, Australia accounts for less than 1% of these global emissions and so the major future gains will need to be achieved through continued international progress. To assist this process, Australia participates in the Multilateral Fund for the Implementation of the Montreal Protocol (which provides funds to help developing countries phase out their usage of ozone-depleting substances).

Because they are highly stable, ozone-depleting substances will persist in the atmosphere for decades to come despite concerted international action to reduce their usage. There is, therefore, a lag between action addressing ozone-depleting substances and recovery of the ozone layer. Based on projections of future levels of ozone-depleting substances in the stratosphere, the recovery of the ozone layer over much of Australia is likely by 2049, and over Antarctica by 2065. However, the continued accumulation of greenhouse gases (especially nitrous oxide) is changing the temperature and thus the rate of chemical reactions in this region of the atmosphere, which may push full recovery beyond 2050, and possibly to 2100 (Chipperfield & Randel 2003; Fraser 2003).