Illustrative Case Constraints on Land Based Options

In this section we consider, as an illustrative case, the inclusion of land management as part of a portfolio of mitigation strategies to close the carbon gap defined earlier. Future scenarios such as the A1, A2, B1, and B2 scenario families (see Nakicenovic et al. 2000 and Figure 6.3) allocate different amounts of land for carbon mitigation strategies (such as cropland for biofuels), while also allowing for an increase in agricultural land to meet the food demands of a growing population. Globally, in 1990, 11 percent of the land surface (1,500 Mha) was under cropland. By 2100, cropland area is projected to increase to about 15 percent (A1), 17 percent (A2), 9-10 percent (B1), 16 percent (B2), and up to 24 percent under some A1 variants (Nakicenovic et al. 2000).

To illustrate the interactions between opportunities and constraints in carbon management, this section examines how each SRES scenario is likely to place pressure on land for food production as different amounts of land are allocated for carbon mitigation. It then asks two questions: (a) Are the areas of land required for mitigation realistic? (b) Under realistic environmental and sociocultural constraints on land use, what is the sustainably achievable potential for land-based options under each SRES scenario?

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