Carbon accounting is a generic term that refers to the assessment of GHG emissions, based on lifecycle assessment principles, and covers the whole biofuel supply chain and final use. GHG performance is expressed as carbon intensity in grammes of CO₂-equivalent per megajoule of produced biofuel (gCO₂-eq/MJ), which includes all gases with global warming potential. Carbon accounting is already considered in policymaking. Road transport, a significant generator of carbon emissions, is a sector where in the coming five years, nearly 40% of fuel demand will be covered by policies incentivising lifecycle carbon reductions, marking a shift from traditional biofuel blending mandates.

The development and use of transparent and internationally agreed GHG accounting is key for the deployment of sustainable biofuels. Sustainable biofuels play an important role in decarbonising transport. They complement the carbon reductions offered by electric vehicles and other energy efficiency measures in road transport and are expected to play an increasing long-term role in aviation and shipping. Sustainable biofuels can also provide benefits in terms of energy security and job creation, including in rural environments. However, large-scale deployment of biofuels, especially crop-based, raises sustainability concerns in some areas, mainly related to land use, net GHG emission balance, and unintended impacts on biodiversity or food prices. These concerns can undermine the credibility of biofuels as a sustainable option, and in some cases pose a barrier to investment and trade. Using carbon accounting for policymaking purposes is further complicated by mixed reports on biofuel GHG emission results and the lack of consensus across methodologies.

The present study, prepared in support of Brazil’s G20 presidency, examines such complexities and discusses regulatory approaches across regions. The study aims to identify main commonalities and differences between carbon accounting frameworks. It examines the main contributors to biofuel carbon intensity, their impact and the associated level of uncertainty in quantification. The study also reviews potential interventions to improve biofuel carbon intensity and discusses policy implications and priorities.

GHG accounting is handled similarly across most biofuel policy frameworks, except regarding land use change. Results for “core LCA” values (that represent emissions associated with the supply chain, excluding land-use change) can vary widely among similar biofuel pathways, but methodologies are robust, and causes are well understood. The three main causes for the wide ranges in core LCA results are related to regional differences, methodological choices, and data input quality and representativeness. While some regional disparities reflect actual practices and local context (e.g. electricity emission intensity or fertiliser consumption), others can be solved by addressing issues resulting from methodological choices (such as co-product handling methods or system boundary setting) or data quality.

Impacts of land use change can be considerable and are a major source of disagreement across different policy frameworks. Emissions caused by direct land use change (the conversion from a previous non-cropland category to bioenergy cropland) can be observed and quantified. However, indirect land use change (when bioenergy growth generates an indirect expansion of cropland into high carbon stock land elsewhere) deals with international economic dynamics that need to be modelled and cannot be measured or verified. Indirect land use change is the main cause of disagreement around biofuels GHG accounting, due to the high uncertainty of results and the risk of arbitrariness when attributing an indirect land use change (iLUC) value to a certain feedstock and biofuel pathway. This calls for alternative policy approaches.

Biofuel carbon intensity can be improved with supportive policy frameworks and appropriate verification procedures. Several aspects of biofuel production can be improved to reduce GHG emissions. For example, in the cultivation process, which is one of the biggest contributors to biofuel supply chain emissions, several innovative solutions have recently started being introduced. These include adopting more sustainable farming practices like multi-cropping, reduced tillage, and low-emission fertilisers. Applying compost, digestate or biochar, can also contribute to the accumulation of soil carbon stock. Emissions can be further reduced by using renewable energy to supply process heat and electricity demand. New technologies such as carbon capture, coupled with biofuels production, can potentially lead to negative GHG emissions values. However, such interventions are likely to increase costs and require market and policy frameworks that reward biofuel pathways with higher GHG emission reductions, underpinned by measurable and verifiable lifecycle data.

Policies need to enable the measurement and verification of data for GHG accounting. To achieve this, they should be underpinned by methodology and data best practices that support the use of transparent and consistent methodologies. Relevant frameworks should foster consistent application of system boundaries across different biofuel pathways based on various feedstocks (including wastes and residues), manufacturing processes and coproducts, as well as the fossil fuels they replace. Collection and use of data that correctly reflect actual practices and regional conditions should be systematically encouraged.

To significantly accelerate the deployment of sustainable biofuels, policies should stimulate upscaling of the best technologies as well as promoting continuous improvement based on up-to-date GHG performance metrics. More specifically, governments should consider:

• Establishing policies that reward better GHG performance and drive continuous improvement Transparent and consistent GHG accounting, accompanied by robust verification processes as appropriate, should allow policies to differentiate the performance of biofuels and promote continuous GHG emission reductions, regardless of the feedstock or technology.
• Prioritising support to measures with significant GHG reduction potential that can be quantified with high certainty and fostering additional measures with less certain quantification while ensuring robust verification steps. While some GHG emission reduction impacts are easier to quantify, others present less certainty when quantifying GHG emission reduction. For this second group of measures, robust verification and certification is required to double-check their effective GHG emission reduction.   
• Addressing indirect land use change (iLUC) concerns by adopting risk-based approaches in the near term and striving to develop global land use policies over time. Indirect land use change values cannot be measured or verified, only modelled. In the short term, qualitative risk-based approaches offering the additional possibility of complying with the requirements of low-iLUC-risk are a good alternative option. These can address potential impacts and encourage improvement instead of attempting to quantify indirect emissions in terms of gCO₂-eq/MJ for a given biofuel pathway. In the longer term, policies should evolve from modelling impacts to managing the causes of indirect land use change by enforcing everywhere direct land use regulations and supporting improved agricultural land management.

Carbon accounting should be part of a broader portfolio of policies encompassing other sustainability criteria and compliance methods to minimise undesired impacts. Policies should protect food and water security, monitor and shelter biodiversity, while taking other socioeconomic factors into account. Biofuel policies would need to be designed to be flexible during periods of tightness in global agricultural markets, to avoid amplifying the size or duration of agricultural price spikes.

Enhanced stakeholder engagement and international cooperation is key for increasing consensus on carbon accounting for sustainable biofuels. This includes further strengthening active collaboration among international organisations such as the International Civil Aviation Organization (ICAO) and the International Maritime Organization (IMO), fostering cooperation with agriculture policy developers, including biofuels and relevant coproducts in broader policies promoting an integrated circular (bio)economy, and encouraging consistent protocols and regulations for carbon accounting in voluntary carbon markets.