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Compiled by Leon P. Zann
Great Barrier Reef Marine Park Authority, Townsville Queensland
Department of the Environment, Sport and Territories, Canberra (1995)
ISBN 0 642 17391 5
Climate changes over geological and shorter time frames have greatly altered sea levels and coastlines. Only 18,000 years ago, at the end of the last Ice Age, the sea level was at least 130 metres lower than it is today, and it did not reach its present level until around 5,000 years ago. At one stage it may have risen at a rate of 45 millimetres per year! Geologically the present coastline is very young, and is very dynamic.(40),(41)
Figure 85: Sea level has varied greatly in the past 150,000 years. It has stood at the present level for only the past 5,000 years.
It is thought that increasing levels of greenhouse gases (mainly carbon dioxide, methane, and nitrous oxide) from industry and other sources may cause a warming of the atmosphere and climate changes. A rise in the mean sea level due to the thermal expansion of the ocean may occur in the next few decades. A doubling of carbon dioxide in the atmosphere from its pre-industrial level is predicted to increase the average global temperature by between 1.5 and 4.5oC. While the effects will probably not be as dramatic as feared a few years ago, it is possible that climate change and sea level rise will be major issues in coastal zone management in the 21st century.(41)
Figure 86: Trends in the greenhouse gases observed over south-eastern Australia and at the Cape Grim monitoring station.
The Commonwealth Scientific and Industrial Research Organisation's (CSIRO's) recent scenarios, or possible outcomes, of Australia's warming by 2030 AD are between 0 and 1.5oC in the north, and between 0.5 and 2.0oC in the south. Based on 1990 sea levels, the resultant global rise in sea level by 2030 AD could be between 5 and 35 centimetres, and by 2100 AD could be between 15 and 120 centimetres. The lower estimates would cause minor problems; the higher estimates would result in inundation of low-lying areas and serious erosion of coastlines.(41)
Figure 87:Recent trends in sea level changes between 1966 and 1984-85 show that these vary around the coast, with it rising in some places and falling in others. Trends are not long enough to determine changes due to an enhanced greenhouse effect.
Changes in patterns of rainfall and cyclones due to global warming may have a greater impact on coastal environments than sea level rise. Coastal saltmarshes and wetlands, beach processes, coral growth and fisheries productivity may also be affected.(41)
The threat of global climate change requires coordinated global and national efforts. Australia's Greenhouse Response Strategy is linked with the United Nations Framework Convention on Climate Change which was open for signing at the 1992 United Nations Conference on Environment and Development. Commitments of this Convention include preparing national inventories on greenhouse gas emissions and removals by carbon sinks, national programs to mitigate climate change, and promoting ecologically sustainable development.(41)
The Response Strategy provides a means for identifying response measures, including reducing greenhouse gases, scientific research, and planning for change. Major difficulties in planning include the extended time scales involved (spanning many decades: much longer than usually considered by planners), and the great uncertainty about the nature and extent of possible changes.(41)
Systematic monitoring of Australia's climate is undertaken by the Bureau of Meteorology. The composition of greenhouse gases in Australia is being monitored at the Cape Grim Baseline Air Pollution Station.(41)