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ATMOSPHERE

The atmosphere is an essential component of all ecological systems on Earth. Nitrogen and oxygen comprise 99% of the atmosphere. Small amounts of other gases and particles make up the balance. The atmosphere plays a critical role in regulating global, regional and local climate and is essential to supporting life on Earth. Oxygen is required for life, stratospheric ozone protects us from harmful solar radiation and greenhouse gases help maintain a temperature range suitable for life.

This section focuses on the following topics:

• Greenhouse gases are a natural part of the atmosphere. They trap the sun's warmth and maintain the earth's surface temperature at levels able to support life. However, human actions – particularly burning fossil fuels (coal, oil and natural gas) and land clearing – are increasing the concentrations of these gases which mean they trap more heat and change the climate. This is known as the enhanced greenhouse effect, which contributes to global warming. Global warming is widely perceived as one of the most significant international environmental issues. Different greenhouse gases have different effects and remain in the atmosphere for different periods of time. A tonne of methane, for example, contributes as much to global warming as 21 tonnes of carbon dioxide (CO₂). To assess the overall impact of different greenhouse gases, emissions of each gas are converted to a common CO₂ equivalent (CO₂-e) scale and added together.

• Climate change: According to meteorological records, the global average surface temperature has increased over the past 100 years. In Australia, annual average (mean) temperatures have increased, although this has not been uniform throughout the country. The effects of global warming are very difficult to predict. It is likely Australia will be hotter and drier in coming decades according to climate change projections. For most of the last decade, rainfall over south-eastern Australia has been lower than average.

• Air quality is an important factor in the quality of life in Australian cities. The main source of air pollution is motor vehicle emissions. Trends in pollution by fine particles and ozone (a component of photochemical smog) are presented for Australia’s three largest cities. Sulphur dioxide and lead can be emitted in relatively large quantities by mineral ore processing activities, and hence can become a health hazard over some regional centres. Trends in sulphur dioxide pollution over the mining towns of Port Pirie in South Australia and Mt Isa in Queensland are presented.