Multi-Model Assessment of Future Hydrogen Soil Deposition and Lifetime Using CMIP6 Data

Abstract

Atmospheric hydrogen indirectly contributes to greenhouse warming by extending methane lifetime, and increasing stratospheric water vapor and tropospheric ozone. Its main sinks are oxidation with OH, and dry deposition via microbial soil uptake. The latter accounts for approximately $50-90\%$ of the sink and is poorly constrained under present day conditions, with very limited studies on its future evolution. This work uses an offline hydrogen deposition scheme to perform the first multi-model assessment of deposition velocities driven using data from five models from the Coupled Model Intercomparison Phase 6 project. Deposition values calculated from historical data are compared to observations, and deposition velocities are evaluated across four scenarios $\left(2015-2100\right)$. We find deposition velocity increases with time and stronger climate forcing. A 20$\%$ present-day, inter-model discrepancy, linked to differences in soil moisture and porosity, leads to a 33$\%$ variation in hydrogen's global warming potential over a 100-year time horizon.