Hydrogen Emissions: Constraining The Earth system Response (HECTER)

A global hydrogen economy is growing rapidly, facilitating a rise in the atmospheric hydrogen levels. Soil microbes remove a significant but uncertain proportion (50-80%) of hydrogen from the atmosphere, with the remainder being removed through atmospheric chemistry by reacting with hydroxyl radicals (OH). Rising hydrogen levels thus deplete OH, extending methane’s atmospheric lifetime. Additionally, hydrogen oxidation produces tropospheric ozone and stratospheric water vapor, making hydrogen an indirect greenhouse gas (GHG).

The project aims to enhance global modeling capabilities, assess future impacts, and reduce uncertainties related to hydrogen use. Unlike existing models that prescribe surface layer mixing ratios for hydrogen and methane, this project will develop versions of the UK Earth System Modelling project (UKESM) to incorporate hydrogen emissions and deposition, validated against surface observations, aircraft data, and firn ice records.

The results will be synthesized to produce a comprehensive assessment of climate metrics such as Global Warming Potential, Global Temperature Potential, and Effective Radiative Forcing. These findings will be incorporated into the FaIR model, used for policy analysis, allowing exploration of various future hydrogen scenarios, including the offset of other greenhouse gas emissions, leakage levels, and different atmospheric chemistry representations.