Indicator: Ozone Depletion
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Summary of results
The hole in the ozone layer continues to form each Antarctic winter and the year-round total ozone over the ACT remains depleted by about 10–15%. However, the rate of loss, previously about 4% per decade, is now levelling out.
National legislation ensures the control of ozone-depleting substances in the ACT.
Reductions in the rate of Antarctic ozone depletion are starting to be detected and, provided ozone-depleting substances are no longer released, the ozone hole is expected to recover by 2050. Until that time, however, the ACT will continue to suffer levels of ultraviolet (UV) irradiation that are higher than would naturally be expected.
What the results tell us about the ACT
The Environment Protection Act 1997 and the Environment Protection Regulations 1997 provide the legislative framework for the ACT to implement national strategies on ozone-depleting substances. Equipment that uses CFCs, HCFCs or halons must only be serviced by a qualified technician. It is illegal to deliberately release CFCs, HCFCs or halons into the atmosphere except under prescribed circumstances, such as to extinguish fires.
The most commonly used ozone-depleting substances in the ACT have been CFCs and HCFCs (in refrigerators and air conditioners) and halons (in fire extinguishers). The manufacture and importation of CFCs is banned and CFCs are becoming increasingly scarce. In 1996, it became illegal to possess halon fire extinguishing equipment, including yellow (BCF) portable fire extinguishers, without an essential use permit.
The ozone hole
The extent of ozone depletion above the ACT is not directly measured, although there are satellite measurements that apply to the region. Measurements of UV-B at ground level are also useful. Again, there are no data specifically for the ACT, but UV-B is monitored in Melbourne and Sydney and in Berridale, New South Wales.
The NASA TOMS satellite has provided daily ozone data for the ACT since 1996. There is no clear trend from this short time series but there is considerable daily variation. This variation can mask the overall slow trend in ozone decline unless sophisticated statistical analysis is undertaken.
According to Simon Torok of the CSIRO (personal communication), there has been a continuing year-round level of ozone depletion of about 4% per decade since the 1970s at Canberra’s latitude. This means that, as a result of the release of ozone-depleting substances, the year-round level of ozone protection is about 10–15% lower, on average, than the natural level. However, the most recent data from the CSIRO suggest that this slow rate of ozone loss is now levelling out.
Research has confirmed that the rate of ozone depletion in the layer of air between about 35 and 45 kilometres above the ground has been slowing since 1997. This is a slowing in the rate; depletion is still occurring. Indeed, the spring 2003 ozone hole was considerably larger than that in 2002, but smaller than the record hole of 2000.
NASA data indicates that during spring 2002 the ozone hole was the smallest it has been since 1988. In late September 2002 an unprecedented event occurred when the hole split into two. The two holes were relatively small and each contained a zone of air depleted of more than 50% of its ozone. The holes disappeared in early November. Not only was the 2002 ozone hole the smallest since 1988, it was also the shallowest and the shortest-lived.
This is encouraging, but is not necessarily due to progress in the control of ozone-depleting substances. The size, depth and persistence of the ozone hole varies considerably from year to year owing to natural meteorological changes.
Since the Montreal Protocol came into force in 1989, the concentration of ozone-depleting substances in the lower atmosphere has declined. It takes about six years for ozone-depleting substances to be transported into the upper atmosphere where they can destroy ozone. Upper atmospheric ozone-depleting substances have also started to decline as has ozone depletion.
On the basis of current trends, it is expected that the ozone hole will essentially no longer exist by about 2050.
UV varies seasonally
Data collected on the ground in Berridale shows the expected seasonal variation in UV irradiation. However, the data record is insufficient to analyse a trend. Airborne water vapour absorbs widely across the UV spectrum, although considerable radiation can still penetrate clouds when the sun is high in the sky. Normal air also absorbs UV radiation, so areas closer to sea level tend to receive less UV radiation. Conversely, places such as Canberra, at high elevation and with a dry climate, tend to receive more.
Ground-level UV data is not necessarily a reliable indicator of the extent of ozone depletion. This is because the amount of UV at ground level in temperate Australia, as well as being affected by elevation and atmospheric moisture, will also vary according to the random break-up of the ozone hole in late spring. When this happens, masses of ozone-poor air in the upper atmosphere move northwards from Antarctica and drift away. Some years they may move over Australia, and at other times they may not. If an ozone-depleted mass passes over, even if the ozone hole has been comparatively mild, it will increase UV penetration far more in that year’s spring than in springtime of another year which may have spawned a larger hole.
Data sources and references
Data reliability is considered excellent.
Data from Berridale, New South Wales, was collected by Dr Ken Green, of New South Wales National Parks and Wildlife Service.
Journal of Geophysical Research - Atmospheres .
NASA Global TOMS satellite data. NASA data is in the public domain at .
Newchurch, MJ, ES Yang, DM Cunnold, GC Reinsel & Zawodny JM, ‘Evidence for slowdown in stratospheric ozone loss’, accepted, Journal of Geophysical Research, 2003,
Notes about atmospheric ozone
Atmospheric ozone, which protects the surface of the earth from UV radiation, can be destroyed by various man-made chemicals. Use of these chemicals has led to world-wide ozone depletion, and the much-publicised ‘ozone hole’ which forms over the Antarctic during the southern winter. Their manufacture and use has been controlled by international agreement since the 1980s.Ozone-depletion allows more UV through, especially UV-B (280–315 nm wavelength) which can cause skin damage, cancers and eye damage, such as cataracts in humans and animals, and may also damage plant life. Unfortunately, atmospheric ozone is not replenished by ozone emitted from motor vehicles and other sources of pollution. Ozone pollution in our cities is a separate problem.