Future Hydrogen Soil Deposition: Multi-model assessment of hydrogen deposition and lifetime

Alternate energy carriers to fossil fuels are needed to mitigate climate change, of which hydrogen is one candidate if generated sustainably. Atmospheric hydrogen indirectly contributes to greenhouse warming by extending methane lifetime, and increasing stratospheric water vapour 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. The soil sink is a large source of uncertainty in quantifying hydrogen’s climate impact and the H2 global warming potential (GWP).

This work uses an offline hydrogen deposition scheme to perform the first multi-model assessment of deposition velocities driven by physical climate data from 5 models from the Coupled Model Intercomparison Phase 6 project. Deposition values from historical data are compared to observations, and deposition velocities from 4 future scenarios (2015−2100) are assessed. We find hydrogen soil uptake increases over the century, with larger increases under scenarios with stronger climate forcing, leading to shorter hydrogen soil lifetimes. A large discrepancy (20%) between models is attributed to differences in soil moisture and soil porosity, and results in a variation of 33% in the hydrogen GWP under present day condition, with a maximum decrease of 5.3% by the end of the century.