The atmosphere is an essential component of all ecological systems on Earth. The atmosphere surrounding the Earth consists mainly of nitrogen and oxygen. A smaller amount 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, ozone protects us from harmful solar radiation and historically, greenhouse gases have helped maintain a temperature range suitable for life.
Australia has a unique meteorology as a relatively isolated, continental island. Apart from issues associated with global ozone, greenhouse gas changes and volcanic events, Australia experiences no air quality changes that originate from beyond its borders. However, some human activities change the nature of the atmosphere, affecting air quality, levels of ultraviolet (UV) radiation and climate.
The commentary that follows focuses on the following trends:
- Greenhouse gases (GHGs) are a natural part of the atmosphere. They trap the sun's warmth and maintain the Earth's surface temperature at the 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 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 impact of different 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. Rainfall in Australia is highly variable geographically, seasonally and from year-to-year. In recent years, rainfall has been higher over much of northern Australia, especially in the northwest, while south-eastern Australia has been drier-than-average. Some areas have experienced their lowest rainfall on record.
- Ozone near the Earth's surface can be a harmful pollutant, but in the upper atmosphere (the stratosphere) it absorbs most of the harmful ultraviolet (UV) radiation in the sun's rays. When excessive UV radiation reaches the Earth’s surface it can cause problems for human and ecosystem health. Human activity has been responsible for increasing the concentrations of ozone depleting substances in the upper atmosphere. As a result of these emissions, between 2% and 4% of ozone over Australia has been lost each decade since the 1950s and we are now exposed to greater levels of UV radiation than in the past.
- 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 fine particle pollutants, ozone (photochemical smog), motor vehicle usage and sulphur dioxide in regional centres are presented.