Linking forest carbon opportunity costs and greenhouse gas emission substitution effects of wooden buildings: The climate optimum concept

Forests play a crucial role in achieving net-zero greenhouse gas emission targets in the coming decades, as they can act as natural carbon sinks by removing carbon dioxide from the Earth's atmosphere. The use of wood as a building material leads to lower greenhouse gas (GHG) emissions throughout its life cycle compared to other building materials and is therefore considered a valid climate change mitigation strategy. However, the impact of wood harvesting on the potential carbon storage in forests has largely been ignored. In this study, we investigated whether the use of wood as a building material is beneficial for climate change mitigation when considering carbon opportunity costs, which represent the amount of carbon prevented from accumulating in forests due to wood extraction. We introduce the climate optimum concept, which links both GHG emission substitution and associated carbon opportunity cost of wooden buildings. Application of the concept to a case study building shows that the GHG substitution benefits of wooden buildings for climate change mitigation are overshadowed by carbon opportunity costs in forests. In our analysis, no wooden scenario achieves sufficient life cycle embodied GHG emission substitution in order to compensate for the unrealized carbon storage potential in the forest system due to harvest. Wood-based GHG mitigation strategies in the building sector and beyond need to consider this unrealized carbon storage potential of forests expressed via carbon opportunity costs, in order to obtain a more comprehensive picture of the climate impact of forests and wood-based products.