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Discussion of the greenhouse effect and the importance of maintaining a balance of carbon dioxide in the atmosphere. The main gases in the atmosphere that contribute to the greenhouse effect are carbon dioxide, methane and water vapour. The increase in man-made emissions of carbon dioxide is of most concern to scientists. Deforestation has reduced the number of plants removing carbon dioxide from the air through photosynthesis.

Students could investigate sources of CO2 in the atmosphere, both natural and man-made, researching figures on how much carbon dioxide comes from each source. The effect of carbon dioxide on global warming could be modelled by heating plastic bottles filled with air containing different amounts of carbon dioxide and noting any differences.