Waste Valorization for Climate Change Mitigation: A Global Meta-Analysis of the Environmental Performance of Biochar Production Systems

Organic waste management frequently generates substantial greenhouse gas emissions and environmental burdens. Converting waste biomass into biochar has emerged as a promising strategy for waste valorization and climate change mitigation, owing to its carbon sequestration potential and diverse applications across agriculture, environmental remediation, and construction. Despite a growing body of research, a comprehensive quantitative synthesis of the environmental performance of biochar systems remains limited. This study therefore conducted a PRISMA-based meta-analysis of published life cycle assessment (LCA) studies to evaluate the environmental impacts of biochar production, with primary emphasis on global warming potential (GWP), restricted to cradle-to-gate system boundaries. The results indicate that biochar research is concentrated predominantly in developed countries, particularly the USA, UK, Germany, and Canada, underscoring limited adoption in developing regions. Agricultural residues and food waste were the most frequently investigated feedstocks, alongside sewage sludge and municipal solid waste. Electricity was the dominant energy source, though biomass and solar alternatives were also explored. Pyrolysis and hydrothermal carbonization were the most widely applied conversion technologies, operating at mean temperatures of approximately 500°C and 200°C, respectively. Among assessed technologies, torrefaction exhibited the highest mean GWP (2.0 kg CO₂-eq kg⁻¹ biochar), whereas gasification demonstrated the greatest mitigation potential, achieving a mean net GWP of −8.3 kg CO₂-eq kg⁻¹ biochar. Approximately 63% of reported GWP values ranged from 0 to −1.9 kg CO₂-eq kg⁻¹ biochar. Methodological heterogeneity among studies, including variations in system boundaries, functional units, and inventory assumptions, constrained broader comparability. Future research should prioritize standardized LCA frameworks, expanded geographical representation, and evaluation of additional impact categories. Overall, biochar production represents a viable pathway toward sustainable waste management and climate mitigation, particularly when integrated with low-carbon energy systems and optimized conversion technologies.