Published by Australian Academy of Science
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. 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. Climatic zones would be expected to shift – meaning that areas currently too cold for crop growing might develop a warmer summer and a longer growing season. Countries such as Russia and Canada which have extensive areas with permanently frozen soil, might benefit by being able to use these for agriculture.

But rainfall patterns could also change, making some currently viable crop-growing areas hotter and drier until they degenerate into desert. On the other hand, if certain ocean currents change direction then some regions could actually become colder. Other changes could affect the oceans even more drastically.

Whether or not natural ecosystems could adapt readily remains to be seen. Perhaps some could, 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.

Related sites

• Scientific report on climate change makes staggering predictions (transcript of ABC radio's Earthbeat, 4 November 2000)

• Predicting climate change (Oak Ridge National Laboratory, USA)

• Antarctic records of past climate (transcript of ABC radio's Ockham's Razor, 5 December 1999)

• Remembrance of things past: Greenhouse lessons from the geologic record (Consequences: The Nature and Implications of Environmental Change, Winter 1996, US Global Change Research Information Office)

Other boxes

Box 1. Greenhouse gases

Box 2. What is modelling?

Box 4. International deliberations

Box 5. Australia's policy response