Sensitivity of climate effects of hydrogen to leakage size, location, and chemical background

Abstract. Use of hydrogen can reduce carbon dioxide emissions by replacing fossil fuel used as an energy carrier and reactant in metal production. When hydrogen is used, some hydrogen will leak during production, storage, transport, and end use. Via chemical reactions in the atmosphere, the hydrogen will affect the atmospheric composition of methane, ozone, and stratospheric water vapor and hence radiation in the atmosphere. A recent multi-model study found the Global Warming Potential over a 100-year time horizon (GWP100) for hydrogen to be 11.6 ±2.8 (one standard deviation). Here, we use a chemistry transport model to investigate the sensitivity of GWP100 to the magnitude and the location of the hydrogen emission perturbation and the chemical composition of the background atmosphere. We show that the hydrogen GWP100 is linear with respect to size of emission perturbation, is not dependent on where emissions occur except sites far from soil sink active areas, and is not very different for possible futures of the chemical compositions of the atmosphere. We also investigate the methane GWP100 sensitivities on the atmospheric chemical composition, and it increases by up to 3.4 compared to present-day atmospheric composition. Overall, the changes in the hydrogen GWP100 are within one standard deviation of the multi-model GWP100, except for emission perturbations at two distant sites not relevant for a future hydrogen economy. Therefore, it is not necessary to adjust the multi-model GWP values when assessing emissions at different locations or in the future where the atmospheric composition differs from present-day.