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It is emphasized that land requirements for biofuels are likely to be overestimated because we assume ad hoc that a large percentage of biofuels must come from energy crops on new cropland. Some studies contend that large quantities of biofuels can be provided on marginal lands outside of prime cropland (see, for example, Swisher, 1993 and Woods and Hall, 1993). In addition, we only take into account three energy crops, whereas there are many other crops that might be better suited to a particular climate and soil and consequently have higher local yields. Moreover, we do not consider the costs of growing the assumed energy crops, which in reality should lead to efficient use of land.
All other assumptions in this scenario are the same as in the Conventional Wisdom scenario.
IMAGE 2.0 takes into account the growing characteristics of the energy crops and estimates their change in potential productivity as climate changes. As an example, in this scenario the potential productivity of elephant grass increases between the years 1970 and 2100 especially in Canada and Russia due to changes in temperature and precipitation (Figure 16). Changes in productivity, together with the change in demand for these biofuels, leads to the allocation of additional agricultural land for these crops. The reader is referred to Leemans and van den Born (1994) and Zuidema et al. (1994) for descriptions of the methodology for calculations of potential crop productivity and land cover changes.
As to changes in land cover, we again focus on Europe and Africa as examples. Figure 9a depicts the new land cover types that appear between 1990 and 2050 according to the Conventional Wisdom scenario. As noted previously, large new areas of grassland and agricultural land are needed in Africa to satisfy increased food demand, whereas forested areas reappear in Europe because of stabilizing food demand and increased crop yield. Figure 9b shows the additional agricultural areas required in year 2050 for energy crops according to the Biofuels Crops scenario (over and above the new agricultural areas shown in Figure 9a).
In year 2050, 14% more agricultural area is required for biofuel crops in Africa and 71% more for OECD Europe as compared to the Conventional Wisdom scenario (Figures 7a and b). In OECD Europe this leads to deforestation instead of the forestation computed in the Conventional Wisdom scenario. The relatively small increase of agricultural land in Africa for year 2050 can be explained by the relatively small absolute amount of modern biofuels used in the first half of the 21st century. The use of biofuels in Africa becomes more substantial in the second half of the century, and this is reflected in the land cover simulation which indicates large new areas of agricultural land necessary for energy crops (Figure 7b, and compare 9b and 9c). By comparison, the use of biofuels declines in the second half of the century in Europe, and the yield per hectare of energy crops increases because of technology. Consequently, less area is required for biofuels in 2100 than in 2050 (Figure 7a, and compare 9b and 9c).
Not only will Africa require substantial new agricultural areas for biofuels in this scenario, but globally a 20% increase is required for 2050 and 45% for 2100 (Figure 7c, Table 7). Since agriculture replaces forests and other land cover types capable of assimilating more carbon, there is a substantial reduction in the carbon assimilated by the biosphere (Figures 11c and 12a). What follows is an increase in atmospheric CO2 in year 2100 from 777 ppm in the Conventional Wisdom scenario to 821 ppm in this scenario (Figure 13a). This results in a slight increase in temperature for the Northern and Southern Hemispheres, as compared to the Conventional Wisdom scenario (Figure 15, Table 7). Synopsis of Results of Biofuel Crops Scenario
Summing up, following the assumptions of this scenario, the need for biofuels may take up large amounts of new agricultural land in the world. A consequence of expansion of agricultural land is a reduction of the CO2 assimilated by the biosphere, a small increase in atmospheric CO2 as compared to the Conventional Wisdom scenario, and somewhat larger global warming. However, we reiterate that the energy cropland requirements assumed in this scenario may be exagerated since it may be possible to provide a much larger fraction of biofuels from agricultural wastes, plantations on marginal land, and other non-cropland sources (see, for example, Woods and Hall, 1993; Johansson et al. (1993a and b). Moreover, the requirements for land would not have been as large, nor the reduction in C uptake by the biosphere so great, if energy crops/trees had been selected that were better suited to local climate and soil. Perhaps this scenario provides a useful estimate of the upper range of land requirements of biofuels.
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