Search

The demand for wood-based energy is foreseen to grow as energy and climate policies around the world promote the use of bioenergy for climate change mitigation. However, the carbon impacts of forest bioenergy range widely in the literature. The value-choices made on the response of forest management to bioenergy demand have a major influence on the results obtained from modeling exercises and may actually change the contribution of forest bioenergy from climate worsening to climate change mitigation. Despite their relevance, there is very little information, or transparency, as to the empirical basis by which these assumptions are chosen and evaluated against. This study aims to fill in this crucial knowledge gap through a mix of critical review, analysis of historical statistical data, and expert judgement. Several prominent studies reporting climate change mitigation from forest bioenergy in three countries are reviewed: Canada, Sweden, and Southeast USA. This analysis shows that the studies rely on assumptions that bioenergy demand will spur supply responses aimed at more efficient forest management and/or relative increases in forest area. Confronting literature assumptions with trends in historical data, we present the most extensive reality-check of bioenergy literature assumptions to date. We find that studies projecting a large role of forest bioenergy in climate change mitigation rely on assumptions that are too optimistic, at times outright unrealistic. We believe scientists could avoid the misinterpretation of their results and improve the policy relevance of their work by more transparent reporting of: i) value-laden assumptions, ii) their influence on the results, iii) the process and rationale behind such assumptions, especially distinguishing between assumptions that reflect incremental changes in management from assumptions requiring transformational change in several industrial sectors. • Accounted carbon benefits of forest bioenergy depend on underlying assumptions. • Forest bioenergy mitigates climate change only when additional biomass is produced. • Forest management responses assumed in the literature are overly optimistic. • Post Normal Science tools can help scientists avoid misinterpretation of results. • Scientists should better convey that model results are contingent on value-choices. [ABSTRACT FROM AUTHOR]

Displacement of fossil fuels by forest bioenergy can contribute to climate change mitigation by reducing greenhouse gas (GHG) emissions. However, GHG savings are not realised until the avoided fossil emissions offset the loss of atmospheric carbon (C) that would have been sequestered if the biomass was not used for bioenergy (i.e. time to C sequestration parity). We estimated the potential for mitigating GHG emissions and the timing of these atmospheric benefits when substituting conventional natural gas (NG) with renewable natural gas (RNG) produced from different forestry feedstocks within three Canadian provinces, and assessed the uncertainty among these estimates. We calculated the GHG balance of RNG using the alternative fate of biomass and the use of NG as base-case scenarios. Immediate to long-term time to C sequestration parity was typically in the order of residues burned < mill residues < harvest residues decaying on site < salvaged trees. The potential GHG savings from using harvest and mill residues to produce RNG within the three provinces ranged from 52.4 to 77.8 Mt CO 2eq a−1. Sensitivity analyses suggest that time to C sequestration parity in the best-case scenarios relative to the baseline can be reduced up to 17 years by using harvest residues that decay rapidly (based on feedstock species, size and geographic region), and reduced up to 8 years by improving the efficiency of the thermochemical conversion process. These two considerations are key for ensuring significant GHG reductions from RNG use within a timescale that helps Canada meet its GHG mitigation targets. • Immediate GHG benefits for RNG produced with residues otherwise burned on site. • No short-term C sequestration parity time for RNG produced with forest residues. • C sequestration parity time >100 years for RNG produced with salvaged trees. • Potential net GHG savings of 52.4–77.8 Mt CO 2eq.year−1 for RNG use. [ABSTRACT FROM AUTHOR]