scenarios from the Global Scenarios Group (GSG) (Raskin et al., 2002), UNEP's Global Environment Outlook (UNEP, 2002), the Millennium Ecosystem Assessment (MA, 2005a) and some models from Stanford University's EMF-21 Study of the Energy Modeling Forum (e.g., Kurosawa, 2006; van Vuuren et al., 2006). Recent sector specific economic stud­ies have also contributed global land use projections, espe­cially for forestry (Sands and Leimbach, 2003; Sathaye et al., 2006; Sohngen and Mendelsohn, 2007; Sohngen and Sedjo, 2006) (Figure 4-20). Note that some scenario exer­cises are designed to span a range of diverse futures (e.g., SRES, GSG, and MA). For example, under the SRES sce­narios agricultural land area could increase by 40% or de­crease by 20% by 2050. Other scenarios focus on a single projected reference land-use characterization (e.g., GRAPE-EMF21, IMAGE-EMF21, GTM-2007). The more recent scenarios suggest greater agreement than under SRES or GSG, with agricultural land extent stable or growing by 10% by 2050.
     In general, the recent scenarios for agricultural land use (cropland and grazing land) have projected increasing global agricultural area and smaller forest land area. The de­velopments in forest land are, for the most part, the inverse of those for agriculture, illustrating the potential forest con­version implications of agricultural land expansion, as well as providing insights into current modeling methodologies. To date, long-term scenarios have not explicitly modeled competition between land use activities (Sands and Leim­bach, 2003, is an exception). A new generation of global

modeling is forthcoming that will directly account for the endogenous opportunity costs of alternative land uses and offer new more structurally rigorous projections (e.g., van Meijl et al., 2006).
     Projected changes in agricultural land are caused pri­marily by changes in food demand and the structure of production as defined by technology, input scarcity, and en­vironmental condition. Scenarios with a greater extent of agricultural land result from assumptions of higher popula­tion growth rates, higher food demands, and lower rates of technological improvement that limit crop yield increases. Combined, these effects are expected to lead to a potentially sizeable expansion of agricultural land. Conversely, lower population growth and food demand, and more rapid tech­nological change, are expected to result in lower demand for agricultural land.
     There are very few published global scenarios of changes in urban areas (Kemp-Benedict et al., 2002; UNEP, 2004). All show a steep increase over the next decade, with about half estimating a stabilization of urban areas by 2025. Final total urban area is about 50% larger than in 1995. Although the total increase in area is relatively small, the implications for agriculture might be disproportionately large, since most of the urban growth is at the expense of high-value agricul­tural lands.

4.4.3.2 Regional and local changes
Regional and local drivers of land use change are even more complex than global drivers because a large number of di-