Greenhouse gas impact of bioenergy pathways

Wide ranges in emissions

Supply-chain emissions – i.e. emissions from the cultivation, production and transport of bioenergy – could range from around 20 grams of CO₂-equivalent per megajoule (gCO₂eq/MJ) for advanced biofuels to close to 60 gCO₂eq/MJ for ethanol from wheat. The carbon impact for wood pellets ranges from 8 to 30 gCO₂eq/MJ.

Major areas of uncertainty are nitrous-oxide (N₂O) field emissions and the assumed yields of woody crops. Studies using general or partial equilibrium models show land-use-change emissions from various types of conventional bioethanol ranging from 3 to 61 gCO₂eq/MJ; those of conventional biodiesel range from 7 to 94 gCO₂eq/MJ. For biodiesel, the use of peatland plays an important role in the greenhouse gas effects.

Costs, benefits and policies

Bioenergy options can deliver net cost benefits, compared to fossil fuel alternatives, and even more so if greenhouse gas emission reductions are valued in monetary terms. However, costs and benefits largely depend on climate policies, rules and regulations in the countries or sectors involved in the biofuel supply chain. Negative impacts of ambitious bioenergy schemes on natural ecosystems can be reduced significantly through the simultaneous introduction of measures to keep land conversion in check. In particular, schemes to protect forest areas can be instrumental to limit land-use change, leading to beneficial effects for nature protection and biodiversity conservation in highly valued forest areas.