GHG implications of land use and land conversion to biofuel crops

Oct 2008

There are multiple reasons why biofuels are attracting global interest. A systematic assessment of the GHG mitigation potential of biofuels is required because climate change mitigation is either a primary objective or as a co-benefit from other objectives of increased biofuel production.
A life cycle analysis of crop production is a key first step to assess the GHG mitigation potential of biofuels. Biofuels have a net positive effect in displacing GHG emissions from the combustion of liquid biofuels, when considered without their impact on land use. The second step is to assess GHG emissions from the expansion of area under biofuels involving conversion from native ecosystems to biofuel crops. In general, when biofuel cropping is associated with the conversion of native ecosystems, the net GHG balance is negative implying no net immediate climate benefits from shifting to biofuels. The carbon debt of this conversion would have to be re-paid through the extended use of biofuels but requires from few to several hundred years to balance out the initial carbon losses. Ultimately, any major land surface transformation resulting from the broad utilization of biofuels will require an assessment of its impact on the full radiative forcing including changes in surface albedo and water cycling.
The present analysis carried out based on projected diesel and gasoline consumption for 2030 and a targeted petroleum substitution of 10% by biofuels shows that the emissions are likely to be significant. The land required for meeting the targeted biofuel production is in the range of 146 to 600 Mha. The critical issue here is which land category will be converted to biofuel crops and its implications for GHG emissions as well as food production. If currently cropped area or forest land or wetlands are used the implications are likely to be negative for GHG emissions as well as food production. Alternatively, if biofuel production is targeted towards lands previously converted to agriculture, but not currently being used for crop production, such as degraded pasture or abandoned farmland, the GHG and biodiversity consequences will be much more favourable than if biofuel production causes the direct or indirect conversion of natural ecosystems.
Yields of current and potential biofuel crops are likely to increase, but it unclear by how much. If biofuels are produced in ways that minimize conversion of habitat, for example by utilizing waste products or cover crops, significantly increasing yields, and targeting degraded pasture and abandoned cropland, biofuels could play a positive role in mitigating climate change, enhancing environmental quality and strengthening the global economy. This requires significant research, development of sustainable land-use and biofuel production strategies, science-based policy making and enforcement of sustainable production and management practices and policies.

By: N.H. Ravindranath, R. Manuvie, J. Fargione, P. Canadell, G. Berndes et al.

 
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