Recent scenario studies (Hall et al., 2000) show biomass energy contributing 150-200 EJ yr-1 by 2050, avoiding CO2 emissions of ~3.5 Gt C yr-1-more than half of present fossil fuel emissions. Previous global energy scenarios show a rising trend for biofuel use, at small or no additional cost, with Latin America and Africa becoming large net exporters of liquid biofuels. WEC (1993) projects 62 EJ in 2020, plus traditional wood fuel in developing countries; IEA (1998) projects that biomass fuels will grow at 1.2 percent per year to 60 EJ in 2020; Lazarus et al. (1993) project 91 EJ in 2030; Dupont-Roc et al. (1996) showed a business-as-usual scenario for Shell International with 221 EJ-of which 179 EJ were from fuel plantations-in 2060. The Global Energy Perspectives' high-growth, high-biomass scenario has 316 EJ of biomass by 2100 (Nakicenovic et al., 1998). Without arguing these and other numerical scenarios, the common vision is that there is a large and increasing potential for biofuels (see Fact Sheet 4.21 for land-use implications).
Under its Biofuel Activity Program, the International Energy Agency (IEA) monitors a wide range of commercial and near-commercial processes, many of which use small-scale plants for converting biofuel into heat, light, and transportation fuels (Overend and Chornet, 1999; Rosillo-Calle et al., 2000). Walter (2000) reviews new technology. Large sunk costs in long-lived capital stock and infrastructure impedes market entry for renewable energy. Biofuel is relatively compatible, however, with the fossil fuel-based energy systems (e.g., blending with petroleum products, wood chips with coal at power stations). Modern biofuel is efficient at small scales (e.g., in rural areas and developing countries).
In general, land availability (out of the very large area that might be used) will be influenced by its value (opportunity cost) in the variety of services that land provides, from wilderness through food production to urban occupation, as well as by its biomass productivity. The potential for increased production of biofuels can be accomplished through increased use of existing forest and other land resources, higher rates of plant productivity, and more efficient conversion processes and capture of wastes.
Unmanaged woody species have yields of less than 5 t ha-1 yr-1 (dry weight biomass). Optimal management and planting of selected species and clones on appropriate soils currently achieves 10-15 t ha-1 yr-1 in temperate areas and 15-25 t C ha-1 yr-1 in the tropics; 40 t C ha yr-1 has been obtained with Eucalyptus in Brazil and Ethiopia. High yields (30-40 dry t ha-1 yr-1) are also possible with herbaceous crops such as switchgrass (Hall et al., 1992). In Brazil, the average annual yield of sugar cane has risen from 28 to 39 t ha-1 yr-1 (dry weight) over 15 years, with more than 70 t ha-1 yr-1 achieved in Hawaii, southern Africa, and Queensland (FAO, 1999).
There are large areas of deforested and degraded lands in tropical countries that could produce multiple benefits from the establishment of biofuel plantations (Brown, 1998). Conversion of these and other lands to biofuel plantations can provide economic value to the local people. Large-scale biofuel production will require specific energy crops, improved land management, species selection and mixes, genetic engineering, and so forth.
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