Climate Change 2001:
Synthesis Report
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Figure 8-2: This figure shows linkages between climate change and other environmental factors in food supply and demand. Increasing food demand by a growing world population calls for larger food production. This, in turn, brings a series of implications in the use of land, such as converting wildlands to croplands (extensification), and using chemical fertilizers and/or using irrigation to increase yield (intensification) or enabling cultivation in otherwise non-usable land. Expanding the land under cultivation results in loss of biodiversity, as ecosystems are converted to fields growing only a few species (usually exotics). Change of forests to agriculture brings a net loss of carbon to the atmosphere, as forests are replaced by grassland or cropland. This clearing also increases flooding probability, as the agricultural systems retain less precipitation than forests. Intensification of crop production can involve a variety of chemical treatments, most of them being nitrogen fertilizers bringing the side effect of release of nitrogen gas compounds (some of which are strong greenhouse gases) to the atmosphere and nitrogen runoff into watersheds, with many environmental and health implications. The expansion of irrigation affects the supply of freshwater for other uses, leading to shortages and conflicts over water-use rights. Meeting the needs for increased agricultural production has the potential to increase global rates of biodiversity loss, climate change, and desertification. There are interrelations, particularly to water, that underly all these issues, but for simplicity are not shown in the figure.

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