Carbon storage and mitigation potential of structural wood and biochar-based concrete in global urban building scenarios

Abstract

Urbanization is accelerating globally, increasing material demand and associated greenhouse gas (GHG) emissions. Bio-based construction materials can store biogenic carbon within buildings over long periods, yet their net climate change mitigation potential, interaction with circular strategies, and feasibility remain uncertain. Here, we assess biogenic carbon storage and net embodied GHG emissions in global urban building stocks between 2020 and 2100 under material substitution scenarios including structural wood and biochar-based concrete at substitution levels of 10%, 30% and 50%. We further explore the mitigation potential of combining these substitution scenarios with sufficiency and circular economy strategies that reduce floor space demand and material flows. We account for biogenic carbon inflows and outflows, embodied emissions, and feasibility considerations. We find that substituting conventional construction systems with structural wood results in cumulative net carbon storage of 11.0–24.8 GtCO2eq by 2100. These scenarios reduce cumulative net embodied GHG emissions by 20–100 GtCO2eq (−8% to −40%) compared to current construction practices, due to both lower embodied emissions and higher net carbon storage associated. In contrast, substituting with biochar-based concrete achieves more limited cumulative net carbon storage of 7.9–14.5 GtCO2eq and reduces cumulative net embodied emissions by up to 8 GtCO2eq (−4%), constrained by feasible substitution rates in cement needed to maintain structural performance. Combining material substitutions with sufficiency and circular strategies delivers the greatest mitigation potential, lowering cumulative net embodied emissions by up to 64% for wood and 41% for biochar by 2100. Achieving the full carbon storage potential without complementary sufficiency and circular strategies would require substantial expansion of biochar supply, while the feasibility of wood-based storage depends strongly on the level of material substitution. These findings clarify the potential, limits, and feasibility of biogenic carbon storage in urban buildings worldwide.