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In my earlier blog on environmental burden shifting of biofuels, I emphasized the need for developing a holistic framework for low carbon fuel policy to avoid a pitfall that comes with implementing a policy focused on achieving a narrow set of goals, i.e. solving one problem but creating another. A recent EMPA study (2012) that compares 21 biofuel pathways/sub-pathways provides further strong evidence that holistic life cycle thinking is required in devising low carbon fuel policies. The new EMPA study reflects updates to the Eco-invent database since the last version (2007), improved analytical methods and a revised consideration of land use change emissions. The EMPA study argues that while biofuels may reduce global warming and ozone depletion impact compared to using fossil fuels, they generally actually increase a host of other impacts including human toxicity, aquatic eco-toxicity, acidification, eutrophication, land use, and depletion of water, mineral, and fossil resources depending on how feedstocks are cultivated and processed (Fig. 1). This suggests that in the absence of additional sustainability criteria, a single-minded focus on climate change mitigation through biofuels may shift a problem from climate change to other environmental impacts. Indeed, even this burden shifting may be something of a 'best-case' scenario - when indirect land use change is considered, there may not be any benefits at from many biofuels.
GHG emissions from land use change due to biofuel expansion can occur directly and indirectly. The EMPA study considered emissions from direct land use change (dLUC) by looking at the increase in cropland area directly attributable to biofuels, and the corresponding decrease in natural ecosystems such as forestland. For example, emissions from increases in deforestation due to palm oil plantations in Indonesia are counted as dLUC emissions. In countries like the US and EU, where no overall increase in cropland area and no overall decrease in forestland have been observed, EMPA did not include any dLUC emissions in their accounting. EMPA do not attempt to account for iLUC emissions in their assessment, although they do recognize explicitly that if emissions from indirect land use change (iLUC) were included, GHG emissions of some biofuels, particularly first generation food-based biofuels, would increase to the extent that the net benefits as compared to gasoline or diesel may become negative. iLUC occurs when additional land needs to be brought under cultivation to meet demand due to the displacement of existing crops/land uses induced by biofuel production. The EMPA methodology for land use change, in which effectively only feedstocks from the developing world are assigned land use emissions, overstates likely net emissions benefits from US/European biofuels in particular.
The EMPA study compares potential environmental impacts of biofuels with those of petroleum fuels using 16 mid-point impact indicators (Fig. 1). It is evident that food-based biofuels as well as jatropha biodiesel worsen several types of environmental impacts, even if (ignoring iLUC), they may lessen global warming and ozone depletion impacts. Biogas derived from wastes (methane from sludge and wood chips) either have the same or lower environmental impacts in most environmental categories compared to petrol. The advantage of using mid-point impact assessment is that it allows us to identify avenues for reducing an impact of concern through better agricultural practices, use of unused or underutilized land, minimizing fertilizer use, iLUC and deforestation, etc.
From a policy implementation point of view, comparing biofuels on the basis of each of these individual environmental impacts can be challenging since the magnitudes and types of impacts are quite different. As a result end point indicators have been developed to obtain aggregate impacts on human health, natural environment and natural resources. End point indicators are obtained by weighting and normalization of various mid-point environmental impacts. End point indicators are easy to interpret and can be readily used to compare fuels, although they have some limitations resulting from aggregation. There are several methods available for estimating end point impacts include Eco-indicator '99, Swiss ecological scarcity method (UBP 06), and Recipe.
Fig 2 below shows the benefit of informing a policy decision using a more holistic and aggregate environmental impact vs. a single environmental criterion, e.g., global warming potential. Only biofuels in the green shaded area actually deliver overall environmental benefits compared to fossil fuels according to EMPA's metric (UBP 06) – everything else is considered worse on a broad environmental assessment, even where some GHG savings are assumed. The direction of arrows shows changes in estimates from the EMP's earlier study in 2007. It is to be noted that while biofuels such as methane from sludge and manure will have little or no indirect land use change GHG emissions, others such as soybean biodiesel, sugarcane ethanol, and rapeseed biodiesel are associated with iLUC and hence their GHG emissions are underestimated in Fig. 2.
In this particular example, aggregate environmental impact obtained from the UBP 06 method has been plotted against GHG emissions of various fuels. A policy based on GHG emissions only and using the EMPA GHG assessment would incentivize all biofuel except soy biodiesel (Brazil) since they have lower GHG emissions compared to gasoline (petrol). If on the other hand an aggregate environmental impact is considered, there are only a few biofuels from waste and residues that look sustainable (green shaded area). In other words, use of an aggregate environmental score in low carbon fuel policy could help minimize the environmental burden shifting of fuels and promote genuine sustainable as well as low carbon fuels.