Carbon impact of wood-based products through substitution: a review of assessment aspects and future research perspectives in life cycle assessment

Reducing carbon emissions is a top priority for combating climate change, and the use of wood products is one important strategy toward this direction. However, the impact pathways of wood products remain subjective to uncertainties, and there is a lack of consensus over the methodology for assessing impacts. This review focuses on the accounting of benefits, when wood-based products substitute non-wood products. The carbon impact of substitution is measured through the substitution factor (SF), which is derived from a comparative estimation of greenhouse gas (GHG) emissions of wood and non-wood products, using life cycle assessment (LCA). The calculation of SF is influenced by several factors such as system boundaries, functional unit, life cycle stages, product types, substitution assumptions, and end-of-life considerations. This review addresses the previously mentioned challenges and provides a summary of SFs for longer-lived wood products, categorized by product type, system boundary, and country. The findings show that SFs for wood products are higher in construction applications than in interior or furniture uses, with regional variations reflecting differences in the substitution effect. Among product categories, the sawnwood category exhibits the highest SF, followed by engineering wood products and wood-based panels. GHG emissions estimates are sensitive to whether biogenic carbon is accounted for, which in turn influences the respective SFs. Different biogenic carbon accounting methods yield varying outcomes, making this a divisive issue in LCA. Additionally, this review identifies sources of variability and uncertainty in SFs estimation and highlights a range of challenges linked to LCA aspects. Therefore, this review emphasize precautions within the LCA domain to ensure a more realistic estimation of carbon impacts while managing variability and uncertainties.