Greenhouse gas emissions of forest bioenergy supply and utilization in Finland

The paper assesses greenhouse gas (GHG) emissions of forest bioenergy supply and utilization in Finland. Each step in the supply chains of harvesting residues (HR), small-diameter energy wood (EW) and stumps (ST) is assessed separately, with geography-related differences between Northern and Southern Finland (NF and SF) taken into consideration. Furthermore, the GHG performance of five distinct bioenergy options-(1) combined heat and power production, (2) condensing power production, (3) torrefied pellets, (4) gasification, and (5) pyrolysis oil production-is assessed and compared with that of current reference systems in Finland and also the European Union (EU) sustainability criteria. If soil carbon stock (SCS) changes and possible storage emissions are omitted, the GHG emissions deriving from the supply chain of comminuted forest biomass to plants are 2.4, 3.0, and 2.6 gCO2eq MJ−1 for HR, EW, and ST in SF, respectively. In NF, the corresponding values are 2.9, 3.6, and 3.2 gCO2eq MJ−1, respectively. If SCS changes and possible emissions from storage are accounted for, the emissions for HR, EW, and ST are in the ranges 9.2-49.2, 24.4-64.4, and 33.1-73.1 gCO2eq MJ−1 in SF and 12.7-52.7, 29.4-69.4, and 39.5-79.5 gCO2eq MJ−1 in NF. Most supply-chain GHG emissions arise from SCS changes and possible emissions from storage of comminuted biomass, both of which may involve significant uncertainty factors. In comparison to local reference systems, significant GHG savings can be achieved through energy utilization of forest biomass, but if SCS changes and, in particular, storage emissions are taken into account, fulfillment of the EU sustainability criteria is not guaranteed.