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Abstract
Biofuels are receiving growing negative attention. Direct and/or indirect land-use changes that result from their cultivation can cause emissions due to carbon losses in soils and biomass and could negate any eventual greenhouse gas (GHG) reduction benefit. This paper evaluates the implications of land-use change emission on the climate-change mitigation potential of different biofuel production systems in 12 case studies in six countries. We calculated carbon debts created by conversion of different land-use types, ranging from annual cropland to primary forest. We evaluated case studies using three different biofuel crops: oil palm, Jatropha, and soybean. The time needed for each biofuel production system to pay back its carbon debt was calculated based on a life-cycle assessment of the GHG reduction potentials of the system. Carbon debts range from 39 to 1743.7 Mg C0 2 ha -1. The oil palm case studies created the largest carbon debts (472.8-1743.7 t C0 2 ha -1) because most of the area expansion came at the expense of dense tropical forest. The highest debt was associated with plantation on peatland. For all cases evaluated, only soybean in GuarantA£ do Norte and Alta Floresta, Brazil needed less than one human generation (30 years) to repay the initial carbon debt. Highest repayment times were found for Jatropha (76-310 years) and oil palm (59-220 years) case studies. Oil palm established in peatlands had the greatest repayment times (206-220 years). High repayment times for Jatropha resulted from the combined effects of land-cover change and low CO 2 emission reduction rate. These outcomes raise serious questions about the sustainability of biofuel production. The carbon implications of conversion of (semi-)natural systems with medium to high biomass indicate that, in order to generate climate benefits, cultivation of biofuel feedstocks should be restricted to areas that already have low carbon content. © 2011 by the author(s).
Highlights
Biofuels are receiving a lot of attention in the public, private, and scientific domains
The methodology consists of four steps: (a) determining the amount of carbon lost from biomass and soil stocks due to a particular land-use change (LUC) in each case study area, (b) determining an allocation of this carbon debt to the different products and by-products of the biofuel system, (c) determining the annual CO2 reduction rate from substituting biofuels for fossil fuels, and (d) calculating the repayment time of the carbon debt based on the annualized rate of emissions reductions
The largest direct land-use change (dLUC) carbon debts were created in the oil palm case studies, in particular those resulting from the conversion of peatland forest in West Kalimantan, Indonesia
Summary
Biofuels are receiving a lot of attention in the public, private, and scientific domains. Seen as an opportunity to reduce both fossil-fuel dependency and greenhouse gas (GHG) emissions, the use of liquid biofuels—such as biodiesel and bioethanol —as an alternative for transportation fuel is expanding (Verrastro and Ladislaw 2007, Hedegaard et al 2008). Based on these geopolitical and environmental reasons, national and international policies to promote the cultivation and production of biofuels are proliferating. Soybean-based biofuels have an estimated emissions reduction potential of 57% to 74% (Huo et al 2009)
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