Gases in the earth’s atmosphere trap some of the sun’s energy that would otherwise be radiated back into space. This is called the greenhouse effect. This process keeps the earth at a temperature suitable for life. Climate change results from an enhanced greenhouse effect. Increased levels of greenhouse gases (mostly carbon dioxide) in the atmosphere mean that more heat is being trapped and the earth’s temperature is increasing. There is now consensus that emissions from human activities are largely responsible for enhanced levels of greenhouse gasses.

We have already seen evidence of climate change resulting from elevated greenhouse gas concentrations. Since the beginning of last century, air temperature has increased by 0.6°C on average worldwide. In Australia, 2005 was the hottest year ever recorded. The temperature was 1.1°C higher than the average from the previous 30 years.

Continued change will occur in the future

Levels of greenhouse gases continue to increase, and therefore, temperatures around the world continue to rise. The Intergovernmental Panel on Climate Change predict that the average global temperature will rise by 1.4 to 5.8°C by 2100. The Department of Climate Change has worked with scientists to develop models that predict the future climate of Australia. They predict that Australia will warm by 1°C to 6°C by 2070; a slight variation from the global average.

The range in temperature predictions is quite large and there are two main reasons for this. The first is that the climate is very complex and it is difficult to predict how changes in one part of the climate, such as ocean currents, will affect other parts, such as storms. The major source of uncertainty, however, is the human factor. As there is now consensus that humans are contributing significantly to climate change, future actions by governments, societies and individuals will play a large role in determining future climate. The models used to predict temperature must take into account the range of future scenarios of human behaviour.

Changes in the climate that will directly impact the Great Barrier Reef include:

• Increased water temperature
• Increased sea level
• Increased severity of storms and cyclones
• Ocean acidification
• Changed rainfall and runoff
• Changes to the El Niño Southern Oscillation.

The ecological consequences of climate change will be serious. Mass coral bleaching, which is caused by sustained high water temperatures, have already begun to increase in frequency and severity. The range of other potential impacts on the Great Barrier Reef are numerous with many only just coming to light.

Related links

• Management responses