Greenhouse gas impact of bioenergy pathways

12-01-2016 | Publication

This study, commissioned by the International Renewable Energy Agency (IRENA), offers an assessment of the effect of bioenergy on greenhouse gas emissions. It combines estimates of supply-chain emissions from liquid and solid biofuels and direct and indirect land-use-change emissions with different bioenergy pathways: for transport fuel, electricity, and heat. The report also deals with carbon impact, carbon debt and payback times of using energy feedstocks from the forestry sector.

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.