As HUMAN POPULATIONS continue to expand, concurrent increases in energy and food will be required. Consequently, fossil-fuel burning and deforestation will continue to be human-derived sources of atmospheric carbon dioxide (CO_2). The current annual rate of CO_2 increase (~0.5%) from these sources is expected to continue with concentrations exceeding 600 parts per million (ppm) by the end of the current century (Schimel et al., 1996). Because CO_2 absorbs the heat leaving the earth's atmosphere, there is a widespread agreement that increasing CO_2 will result in increasing global temperatures. The extent to which temperatures increase, and the potential biological consequences—from sea-level rise, to the spread of malaria— have been discussed anddebated extensively in both the scientific and popular literature.
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