Unlocking the carbon sink potential of industrial hemp: Cultivation, mechanical decortication, and life-cycle applications

Industrial hemp (Cannabis sativa L.) is gaining attention as a bio-based resource for climate change mitigation, yet its carbon sequestration potential is widely overstated in the literature. Gross sequestration estimates of 9–24.75 t CO₂/ha per growing season reflect biomass carbon uptake before cultivation emissions. Net sequestration after deducting fertilisation, tillage, and transport is approximately 2.46 t CO₂/ha per growing season, which is not exceptional compared with cereal rotation systems. This review synthesises current knowledge of hemp's whole-lifecycle carbon balance, integrating cultivation processes, biomass accumulation, carbon measurement methodologies, mechanical processing, and life-cycle environmental performance. A central conceptual contribution is the characterisation of industrial hemp as a conditional carbon sink and the proposal of a hemp carbon balance (HCB) framework comprising four sequential stages (cultivation, mechanical processing, product use, and end-of-life) that collectively determine whether a hemp system achieves net carbon negativity. Applying this framework reveals that the carbon fate of harvested biomass is most critically determined by decortication method (Stage 2), which governs what fraction of fixed carbon enters long-lived products versus short-cycle streams. However, no existing study quantifies this trade-off in carbon-commensurable units, which represents a major unresolved gap in hemp carbon accounting. At Stages 3 and 4, product end-use and lifespan also drive the greatest divergence, for example hempcrete and insulation products retain biogenic carbon for 50–100 years with consistently net-negative lifecycle, while hemp paper returns cultivated carbon to the atmosphere. Based on current research in this field, future studies should prioritise standardised biogenic carbon accounting protocols, decortication energy-carbon trade-off quantification, belowground carbon dynamic characterisation across soil types and climates, and hemp-specific process model parameterisation to enable reliable whole-system carbon budgets and credible integration of hemp into carbon markets and climate policy frameworks.