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Abstract With increasing global interest in molecular hydrogen to replace fossil fuels, more attention is being paid to potential leakages of hydrogen into the atmosphere and its environmental consequences. Hydrogen is not directly a greenhouse gas, but its chemical reactions change the abundances of the greenhouse gases methane, ozone, and stratospheric water vapor, as well as aerosols. Here, we use a model ensemble of five global atmospheric chemistry models to estimate the 100-year time-horizon Global Warming Potential (GWP100) of hydrogen. We estimate a hydrogen GWP100 of 11.6 ± 2.8 (one standard deviation). The uncertainty range covers soil uptake, photochemical production of hydrogen, the lifetimes of hydrogen and methane, and the hydroxyl radical feedback on methane and hydrogen. The hydrogen-induced changes are robust across the different models. It will be important to keep hydrogen leakages at a minimum to accomplish the benefits of switching to a hydrogen economy.

H2 has the potential to become the green, low-carbon fuel of the future. However, hydrogen emissions impact atmospheric methane (CH4). Bertagni et al. investigate the fate of atmospheric CH4 in scenarios of H2 economy.

Transitioning to a hydrogen economy has the potential to mitigate carbon dioxide emissions. The hydrogen leakage rate and the production pathways appear, based on simulations with a global model, as key leverages to reach a clear climate benefit from a large-scale transition to a hydrogen economy.