Future environmental impacts of global hydrogen production†

Low-carbon hydrogen (H₂) will likely be essential in achieving climate-neutrality targets by 2050. This paper assesses the future life-cycle environmental impacts of global H₂ production considering technical developments, regional feedstock supply, and electricity decarbonization. The analysis includes coal gasification, natural gas steam methane reforming, biomass gasification, and water electrolysis across 15 world regions until 2050. Three scenarios of the International Energy Agency are considered: (1) the Stated Policies Scenario (STEPS), (2) the Announced Pledges Scenario (APS) that entails aspirational goals in addition to stated policies, and (3) the Net Zero Emissions by 2050 Scenario (NZE). Results show the global average greenhouse gas (GHG) emissions per kg of H₂ decrease from 14 kg CO₂-eq. today to 9–14 kg CO₂-eq. in 2030 and 2–12 kg CO₂-eq. in 2050 (in NZE/STEPS). Fossil fuel-based technologies have a limited potential for emissions reduction without carbon capture and storage. At the same time, water electrolysis will become less carbon-intensive along with the low-carbon energy transition and can become nearly carbon-neutral by 2050. Although global H₂ production volumes are expected to grow four to eight times by 2050, GHG emissions could already peak between 2025 and 2035. However, cumulative GHG emissions between 2020 and 2050 could reach 39 (APS) to 47 (NZE) Gt CO₂-eq. The latter corresponds to almost 12% of the remaining carbon budget to meet the 1.5 °C target. This calls for a deeper and faster decarbonization of H₂ production. This could be achieved by a more rapid increase in H₂ produced via electrolysis and the additional expansion of renewable electricity. Investments in natural gas steam methane reforming with carbon capture and storage, as projected by the IEA, seem risky as this could become the major source of GHG emissions in the future, unless very high capture rates for CCS are assumed, and create a fossil fuel and carbon lock-in. Overall, to minimize climate and other environmental impacts of H₂ production, a rapid and significant transition from fossil fuels to electrolysis and renewables accompanied by technological and material innovation is needed.