One method of reducing or stabilizing atmospheric carbon dioxide levels is to trap and lock away carbon dioxide produced by the large carbon dioxide emitters such as power generation and cement works (Fig. 3.10). It is clear that electricity generation, particularly using coal, is the largest stationary source of carbon dioxide, followed by cement production and refineries.

Carbon sequestration can be defined as stable storage of carbon, but it has been suggested that storage in soil and plants cannot be regarded as stable as microbial degradation can lead to carbon dioxide release. However, the degree of permanence can vary greatly with carbon sequestered in soils with some components lasting up to 1000

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Fig. 3.11. Various methods that could be used for carbon dioxide sequestration from a large stationary source of carbon dioxide.

The possible methods of sequestering carbon dioxide from stationary sources are as follows (Fig. 3.11):

• Carbon capture and storage in the deep oceans, oil and gas reservoirs, aquifers and coal beds (geosphere sink).

• Planting more trees or reforestation (biosphere sink).

• Chemical sequestration (material sinks).

• Trapping the carbon dioxide in material such as plastics (material sinks).

• Agricultural practices (biosphere sink).