Missed Opportunities Forgo One-Third of Mass Timber’s Carbon Storage Potential

Abstract Building materials are increasingly positioned as a scalable option for carbon dioxide removal (CDR). Carbon-storing engineered wood products, such as structural mass timber, will be instrumental for CDR. However, system-level perspectives can overlook operational choices that forfeit storage potential. Using stage-resolved life-cycle inventories, scenario-aware uncertainty analysis, and dynamic carbon accounting, we trace carbon flows across mass timber supply chains in the United States, from harvest slash and mill residue to wood products through end-of-life. Across modeled deployment scenarios, we show that management decisions, not technical limits, cut 1.4–2.6 gigatons (Gt) of CO2e storage by 2120, corresponding to roughly one-third of mass timber’s storage potential. Globally, storage losses from these choices could reach 3.8–12 Gt CO2e. We outline a storage-first pathway including slash pyrolysis, diversion of mill residue from bioenergy to wood panel markets, and reuse or pyrolysis at end-of-life. Together, these strategies redirect carbon into value-added, long-lived pools rather than short-lived fates, showing that release timing and supply chain routing choices can matter more than production decarbonization in shaping warming outcomes under mass timber deployment. If implemented, these choices recover forgone storage and aid in developing the built environment as a durable carbon reservoir.