The contribution of bioenergy to the decarbonization of transport: a multi-model assessment

The expected growth in the demand for mobility and freight services exacerbates the challenges of reducing transport GHG emissions, especially as low-carbon alternatives to petroleum fuels are limited for shipping, air and long-distance road travel. Biofuels can offer a pathway to significantly reduce emissions from these sectors, as they can easily substitute for conventional liquid fuels in internal combustion engines. In this paper we assess the potential of bioenergy to reduce transport GHG emissions through an integrated analysis leveraging various assessment models and scenarios, as part of the 33rd Energy Modeling Forum study (EMF-33). We find that bioenergy can contribute a significant, albeit not dominant, proportion of energy supply to the transport sector: in scenarios aiming to keep the temperature increase below 2°C by the end of the 21st century, models project that bioenergy can provide in average 42 EJ/yr (ranging from 5 to 85 EJ/yr) in 2100 for transport (compared to 3.7 EJ in 2018), mainly through lignocellulosic fuels. This is 9-62% of final transport energy use. Only a small amount of bioenergy is projected to be used in transport through the electricity and hydrogen pathways, with a larger role for biofuels in road passenger transport than in freight. The association of carbon capture and storage (CCS) with bioenergy technologies (BECCS) is a key determinant in the role of biofuels in transport, because of the competition for biomass feedstock to provide other final energy carriers along with carbon removal. Among models that consider CCS in the biofuel conversion process the average market share of biofuels is 21% in 2100, compared to 10% for models that do not. Cumulative direct emissions from the transport sector account for half of the emission budget (from 300 to 670 out of 1,000 GtCO2). However, the carbon intensity of transport decreases as much as other energy sectors in 2100 when accounting for process emissions, including carbon removal from BECCS. Lignocellulosic fuels become more attractive for transport decarbonization if BECCS is not feasible for any energy sectors. Since global transport service demand increases and biomass supply is limited, its allocation to and within the transport sector is uncertain and sensitive to assumptions about political as well as technological and socioeconomic factors.