A model-based assessment of the effective radiative forcing of hydrogen: preliminary results from the HYDRA Project

We present preliminary results from the EU HYDRA Project (Hydrogen Economy Benefits and Risks: Tools Development and Policies Implementation to Mitigate Possible Climate Impacts), focusing on the effective radiative forcing (ERF) associated with atmospheric hydrogen emissions. The ERF is quantified using a modelling framework that combines state-of-the-art chemistry transport models (CTMs) for the troposphere (FRSGC/UCI) and stratosphere (SLIMCAT) with a global atmospheric general circulation model (AGCM; OpenIFS cycle 48r1). The CTMs are perturbed relative to 2010 reference conditions by imposing a 100 % increase in surface hydrogen concentrations. The resulting chemical responses of key radiatively active species—ozone, methane, and water vapour—are then used to force the AGCM. Simulations are performed with fixed sea-surface temperatures and sea-ice cover to isolate the effective radiative forcing. The ERF is diagnosed as the top-of-atmosphere (TOA) energy imbalance, computed as the difference in net TOA radiation between the perturbed and control simulations representative of 2010 conditions. In addition, we quantify the individual contributions of ozone, methane, and water vapour to the total ERF.