Increasing the use of wood in construction results in various benefits, such as productivity gains through industrial prefabrication and opportunities for architectural design. However, the main motive for promoting wood construction is reducing the massive climate impact of the construction sector.
In the title of our most recent paper , we ask, “Does expanding wood use in construction markets contribute to climate change mitigation?” To the surprise of many, the answer is far from clear. Thus, with the dichotomic wording of the title, we wish to spark interest and action—not polarization—towards the climate change mitigation debate. Essentially, there is no singular catch-all answer, as it depends on a myriad of assumptions.
Despite the uncertainties, there is plenty of evidence on the climate change mitigation potential of wood construction. Here, we summarize five fundamentals explaining why, on the one hand, wood construction is seen to mitigate climate change, and on the other hand, climate benefits are realized only with long delay:
1. Wood brings substitution benefits, if the wood-based product replaces a more fossil-intensive non-wood product. One example are multi-story residential buildings. Comparative life cycle assessment (LCA) studies often report a 30-50% emission reduction potential for these wooden buildings . The saving occurs during the production phase, through avoided fossil-based emissions called substitution impacts. Crucially, these comparisons concern only fossil emissions and neglect biogenic emissions and removals. This means the temporary carbon storage in wood products and the forest carbon sink is unaccounted for. Thus, the often cited 20-50% emission reduction does not equal the climate change mitigation potential of wood construction, rather it compares only fossil-based emissions. To assess the climate change mitigation potential of wood construction, it is necessary to evaluate both the substitution impacts and changes in the biogenic carbon stocks across both the wood-based production system and the forest ecosystem.
2. Wood products store carbon. However, as per the IPCC guidance for reporting harvested wood product pool emissions and removals , the amount stored in the building stock is obsolete. Only the difference between the annual inflow to- and outflow from- the wood product pool (e.g., building stock) matters. The same principle applies for forest carbon sinks. Forests store billions of cubic meters of biogenic carbon, but when assessing climate change mitigation, only the annual change to the biogenic carbon stock (i.e., net removal) matters.
3. What is climate change mitigation? Firstly, climate change mitigation requires additional efforts. That is, mitigation can only occur through net emission reduction compared to a business-as-usual (baseline) scenario. Secondly, in line with the Paris Agreement, the reduction of net emissions needs to occur within such a timeframe that global warming remains below 2 ⁰C. Studies show invariably that an increase in the level of harvest, compared to business-as-usual, leads to an increase in the atmospheric GHG concentration at least for several decades . The reason is that the substitution impacts and the wood product carbon storage are not large enough to compensate for the reduced forest carbon sink.
4. The trade-off between short and long-term net emissions concerns all wood uses, including wood construction. This is because wood construction cannot be treated separate from other wood uses. One reason is that it is impossible to harvest only the thickest part of the tree (the log covering roughly 70% of the roundwood volume) and leave the rest of the tree which cannot be used to produce sawnwood (pulpwood, tree tops, and branches) to grow in the forest. During sawmilling, 50% of the log is lost as byproducts (chips, sawdust, bark) from sawmilling. These byproducts are typically used for energy, which generally has a lower substitution benefit than material applications. Of the remaining finished sawnwood, approximately 70% is utilized in the construction sector, and a varying fraction of this in long-lived structural frames. Ultimately, increasing sawnwood processing usually requires increased harvest that also leads to increased production of all other wood products, including energy, communication and hygienic papers, packaging products, etc.
5. The above holds, if increased demand leads to increased harvest. However, by applying wood cascading principle where byproducts are used for long-lifetime/high substitution potential applications (e.g. composites, panels, chemicals and textiles) the potential to mitigate climate change increases. Also, if part of the increasing demand was satisfied by reducing the use of wood in another application, it would be possible to increase the average substitution impact and average product longevity without negative consequences on forest carbon sinks – thereby gaining more benefits from a single cubic meter of wood. The feasibility of shifting the end uses of wood is contingent on a complex interplay of supply and demand, but such scenario might not be too farfetched, given the surprisingly small amount of wood required for construction. Quick calculations indicate that a 100% market share of wood in the residential multi-story building sector would imply an around 1.5-5 Mm3 additional log demand in Finland, and 35-100 Mm3 in the EU, depending on the structural frame type. In Finland, a 10% change in the log-pulpwood ratio of harvest, achieved, e.g., through extended rotation periods, could increase the log supply by around 3 Mm3 . Based on this, one could conclude that even a dramatic increase in the market share of wood in the Finnish construction market could be satisfied without additional harvest, through changes in product portfolios and forest management, if only the markets allow. Of course, the annual harvest in Finland is already quite close to the annual timber growth, so major increases in harvest levels would also violate the core principle of sustainable forest management (sustained yield).
The above suggests that wood construction – as well as textiles and other applications with a view on substituting more fossil-intensive materials – can contribute to climate change mitigation in a meaningful time frame, but only on the premise that it does not reduce the forest carbon sink compared to business as usual. That is, while construction is one of the most attractive uses of wood, it is no different from other wood uses in that the overall climate impact remains contingent on the impact to forests. Thus, circular economy efforts are needed to avoid negative trade-offs.
The following management and policy implications arise:
1. Expanding wood use in the construction sector should not inflict major increases in harvest, or the impact of such an increase ought to be carefully assessed against zero emission trajectories. If it was possible to shift the use of wood from one application to another without harvesting more wood, then increasing the market share of wood in construction could bring immediate climate benefits. Alternatively, or in addition to the above, more sawmilling by-products should be directed to high substitution / long-lifetime material applications (cascading principle).
2. We focused only on the fundamentals and therefore cover only part of the uncertainties related to wood product substitution and overall climate change mitigation potential. Even though single peer-reviewed studies cannot include all aspects, decision-making ought to cover also aspects related to, e.g., indirect impacts of changes in markets (leakages and rebound effects), the increasing threat of forest disturbances (adaptive forest management), the development of technological carbon capture and storage or other similar breakthrough technologies, financial incentives and feasibility of mitigation and adaptation strategies, synergies and trade-offs with other sustainable development targets (notably biodiversity), etc. . The net impact, considering all of this, remains uncertain, in particular in terms of what would have happened if not expanding the use of wood. However, this should be no excuse for inaction.
3. Therefore, researchers, industries and governments should increasingly investigate the trajectory of the absolute emissions and removals beyond sector boundaries to assess the likelihood of, and committing to, achieving carbon neutrality by 2050. This requires taking a more material neutral stance across all sectors.
Elias Hurmekoski, Academy research fellow, University of Helsinki
Janni Kunttu, Postdoctoral researcher, University of Helsinki
 Hurmekoski, E., Kunttu, J., Heinonen, T., Pukkala, T., Peltola, H., 2023. Does expanding wood use in construction and textile markets contribute to climate change mitigation? Renewable and Sustainable Energy Reviews 174, 113152. https://doi.org/10.1016/j.rser.2023.113152.
 Duan, Z., Huang, Q., Zhang, Q., 2022. Life cycle assessment of mass timber construction: A review. Building and Environment 221, 109320. https://doi.org/10.1016/j.buildenv.2022.109320.
 Rüter, S., Matthews, R.W., Lundblad, M., Sato, A., Hassan, R.A., 2019. Chapter 12: Harvested Wood Products, in: 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change, 12.1‐12.49.
 Seppälä, J., Heinonen, T., Pukkala, T., Kilpeläinen, A., Mattila, T., Myllyviita, T., Asikainen, A., Peltola, H., 2019. Effect of increased wood harvesting and utilization on required greenhouse gas displacement factors of wood-based products and fuels. Journal of Environmental Management 247, 580-587.
 Hurmekoski, E., Myllyviita, T., Seppälä, J., Heinonen, T., Kilpeläinen, A., Pukkala, T., Mattila, T., Hetemäki, L., Asikainen, A., Peltola, H., 2020. Impact of structural changes in wood-using industries on net carbon emissions in Finland. Journal of Industrial Ecology 24, 899-912.
 Hurmekoski, E., Kilpeläinen, A., Seppälä, J. 2022. Climate change mitigation in the forest-based sector: a holistic view. In: Hetemäki, L., Kangas, J., Peltola, H. (Eds.). Forest Bioeconomy and Climate Change. Springer, Managing Forest Ecosystems. Managing Forest Ecosystems, Springer. Available at: https://link.springer.com/book/10.1007/978-3-030-99206-4