The atmosphere surrounding our planet is composed of a number of different gases, mostly nitrogen and oxygen, with much smaller concentration of other gases, such as carbon dioxide and ozone.

These gases each play a role in supporting life on earth, for example: oxygen is breathed in to fuel chemical reactions in the bodies of animals; a layer of ozone, 15 to 30 kilometres above us in the stratosphere, shields us from harmful ultraviolet-B (UV-B) rays from the sun; and greenhouse gases, predominantly carbon dioxide, maintain the surface temperature of the earth at an average 15°C.

Some of the things that we do changes the nature of the atmosphere - impacting on air quality, the levels of UV radiation reaching the earth and the climate that all plants and animals depend upon.

The main sources of pollution affecting air quality in the Adelaide metropolitan area are motor vehicles, while in regional centres industry has the largest impact. The Environment Protection Authority monitors pollutants in a number of metropolitan and regional locations to determine whether the air quality is good enough to maintain human health. Air quality in most areas of South Australia is generally good, although there are occasions when levels of pollutants fail to meet national guidelines.

Unlike air quality issues, which are generally localised, ozone depletion and climate change are global problems that the whole world contributes to, and feels the effect of. Worldwide problems require solutions that involve every country, and Australia must play its part.

Ozone depletion damages plants, including agricultural crops and creates health problems for humans, including eye damage and skin cancer. Following the implementation of international controls, Australia's (and the world's) emissions of ozone depleting substances have reduced dramatically and it is expected that the first signs of ozone layer recovery will be noticed in the next 10 to 15 years. Full recovery of the ozone layer is expected by 2050 but may be delayed by as much as 50 years, due to climate change and the use of ozone depleting substances in developing countries.

Emissions of greenhouse gases from around the world continues to increase. The use of fossil fuels in transport as well as in domestic and industrial energy consumption (such as electricity from fossil fuel power stations and the use of natural gas), are the biggest contributors to greenhouse gas emissions. As part of the Kyoto Protocol, Australia is expected to reduce greenhouse gas emissions to 8% above 1990 levels by 2008-2012. Australia has signed the Protocol, but has not yet officially ratified (legally accepted) the target. The latest figures available for South Australia indicate an increase of 7.8% in greenhouse gas emissions between 1995 and 2000/01.