In practice, two LCA methods can be distinguished. The attributional LCA is concerned with evaluation of a given product without any consideration of the interactions with a more global system such as the socioeconomic system or the agricultural system. Furthermore, this type of LCA is not in a comparative framework. For example, its purpose could be to improve a given pathway. In that case, the reference system is a baseline of the pathway. However, the public debate on biofuels is rather related to their "renewability" and carbon neutrality. For that reason, a more open methodology is required closed to the consequential LCA. Finally, it is proposed to include these two methodologies into a more general one based on system analysis. In the proposed methodology, the performance indicators are defined by comparing the studies system with a reference or baseline system. In most studies, the reference system is implicitly limited to a fossil fuel pathway (e. g., gasoline or diesel). In various cases, however, this picture is not complete: for example, when coproducts from the biofuel pathway replace an existing product whose performances are significantly different. In this situation, a refer­ence substituted product should be defined. The same applies to the case when the produc­tion of feedstock for biofuels uses land that was previously storing carbon such as forests or grasslands. In this case, a "previous land-use" baseline should be included in order to deter­mine the carbon emissions from this change of land use. When the same feedstock or the land was previously used for another purpose, an "alternative biomass use" or "alternative land use," respectively, may be included in the baseline in order to estimate the effects due to indi­rect land-use changes. The choice to include or not an "alternative use" depends on the assumption made concerning the substitution versus the addition of products. For example, if biofuels substitute overproduced food crops, there is no requirement for additional resources for replacing the substituted products. Conversely, in case of underproduction due to biofuels, additional resources of land or imported products will be required.

In the past, the land-use baseline was included (in a simplified way) in a very limited num­ber of the LCA studies (e. g., ADEME, 2010; CONCAWE-EUCAR-JRC, 2008; GM-LBST, 2002; VIEWLS, 2005). In these three cases, the land used for growing energy crops was considered to be initially set aside (incl. extensive green crop cover with no farming inputs), and conse­quently no alternative use of land or biomass was assumed.