Enhanced greenhouse effect – a hot international topic
Box 3 | Global warming and climate change
An average global temperature rise of just 0.2 to 0.3°C per decade over the next hundred years could have severe consequences, because some regions will experience a much higher than average increase. Even a slight average temperature change can affect the weather in particular regions and this is already happening. According to the Intergovernmental Panel on Climate Change (IPCC) between 1956 and 2005 average global temperatures increased at a rate of 0.13°C per decade. During this period there has also been an increase in extreme weather events like droughts, floods and heatwaves in some regions. And since 1970 there has been a trend towards more intense tropical storms and hurricanes. Rainfall patterns have also changed, making some areas hotter and drier while others have become wetter. Scientists predict that if certain ocean currents change direction then some regions could actually become colder. The El Nino Southern Oscillation is a good example of how a comparatively slight change in one place can lead to major droughts or floods in another.
Evidence that the climate is changing is shown in the melting of ice-sheets and snow, warming oceans and rising sea levels. Other changes could affect the oceans even more drastically by increasing its acidity and the number of coral bleaching events.
With climate change climatic zones would be expected to shift – meaning that some species (including farmed species) may no longer be able to survive in their current locations. Whether or not natural ecosystems can adapt readily remains to be seen. Perhaps some can, but certain species, tolerant of only a narrow band of temperature and unable to move their range fast enough, could become extinct.
Predicting the future is difficult
While the basic physics of the greenhouse effect is well understood, predicting the future course of events is made difficult because of our insufficient knowledge about the detailed behaviours of the atmosphere and oceans. There are at least five areas of incomplete understanding:
- sources (places of origin) and sinks (places of storage) of
greenhouse gases – which affect predictions of future concentrations;
- clouds – which strongly influence the magnitude of climate
change;
- oceans – which influence the timing and patterns of climate
change;
- polar ice-sheets – which affect the predictions of sea-level
rise;
- land surface processes and feedback (when the output of a system affects the input) – which affect hydrological and ecological processes.
There are also limitations to the computer models which are used to simulate an Earth-atmosphere system.
Boxes
Box 1. Greenhouse gases
Box 2. What is modelling?
Box 4. International deliberations
Box 5. Australia's policy response
Related sites
Climate Change and Variability (Australian Government Bureau of Meteorology)
"Does it matter?" ( Natural Environment Research Council, UK)
Climate change 2007: The physical science basis (Intergovernmental Panel on Climate Change)
Global climate change (British Broadcasting Corporation, United Kingdom)
Page updatedFebruary 2012.