A Life Cycle Assessment Review of Climate Impacts from Low-Carbon Hydrogen Production Technologies

Hydrogen is emerging as a key energy carrier for achieving net-zero emissions in an energy system where fossil fuels still provide about 80% of global primary energy and remain the dominant source of greenhouse gas emissions. Even if all currently announced projects are realized, low-emission hydrogen production is projected to reach only about 49 Mt yr^–1 by 2030, revealing a substantial decarbonization gap. Green hydrogen from renewable-powered electrolysis is identified as the most sustainable long-term pathway, with project pipelines indicating potential expansion of global electrolyzer capacity to nearly 520 GW by 2030, although high capital costs and the pace of renewable deployment remain key constraints. Blue hydrogen, produced via steam methane reforming with carbon capture and storage, can serve as a transitional option but achieves genuinely low life cycle emissions only under stringent operating conditions such as very low methane leakage and high CO₂ capture efficiencies, and its relative advantage is expected to decline as power systems decarbonize. Biomass-based hydrogen offers a complementary route by coupling renewable hydrogen production with waste valorization and nutrient recovery, particularly in regions with abundant bioresources. Using life cycle assessment, supported by techno-economic insights and emerging digital tools such as artificial intelligence and machine learning for process optimization and emissions monitoring, this review identifies quantitative thresholds and strategic priorities for scaling sustainable, low-carbon hydrogen systems within evolving global policy and market frameworks out to 2030 and beyond.