Estimating the climate impacts of hydrogen emissions in a net-zero US economy

Abstract Hydrogen is not a greenhouse gas, but its interactions with other species in the atmosphere indirectly induce radiative forcing. This study evaluates the relative impacts of hydrogen emissions across 23 different net-zero scenarios from five prominent US economy-wide analyses. Hydrogen emissions associated with venting and leakages across energy supply chains are considered. The magnitude of these energy-related hydrogen emissions is estimated and compared to the remaining positive energy-related carbon dioxide and methane emissions in the 23 US net-zero scenarios. This methodology facilitates consideration of the potential magnitude of hydrogen emissions relative to the other emissions reductions and/or carbon dioxide removal strategies that would be required to balance those hydrogen emissions across a wide range of possible net-zero scenarios. Magnitudes of energy-related hydrogen and methane emissions are estimated for each scenario across a range of possible emissions rates (Low, Central, and High) and global warming potentials based on literature. The results indicate that when evaluated over a 100 year horizon, hydrogen emissions span a range of 0.02–0.15 Gt CO2e yr −1 and are lower than remaining positive carbon dioxide emissions in the Central emissions case of all 23 scenarios. In the 19 scenarios that do not constrain fossil fuels, hydrogen emissions (0.02–0.11 Gt CO2e yr −1 ) account for less than 14% of combined hydrogen, methane, and carbon dioxide emissions. The four scenarios that constrain fossil fuels have higher levels of hydrogen consumption and correspondingly higher levels of hydrogen emissions (0.10–0.15 Gt CO2e yr −1 ). These results suggest that hydrogen emissions are non-negligible in net-zero energy systems; however, the potential climate impacts associated with hydrogen emissions can be balanced through relatively small reductions in remaining positive emissions and/or increases in carbon dioxide removal. Further effort is needed to advance hydrogen emissions measurement, quantification, and mitigation strategies to maximize the potential climate benefits of hydrogen for decarbonization.