Liquid Hydrogen: A Mirage or Potent Solution for Aviation's Climate Woes?

The aviation industry faces a formidable challenge to cap its climate impact in the face of continued growth in passengers and freight. Liquid hydrogen (LH) is one of the alternative jet fuels under consideration as it does not produce carbon dioxide upon combustion. We conducted a well-to-wake life cycle assessment of CO emissions and non-CO climate change impacts per passenger-distance for 17 different hydrogen production routes, as well as conventional jet fuel and biofuels. Six other environmental and health impact categories were also considered. The Boeing 787-800 was used as the reference aircraft, and a range of flight distances were explored. Contrail cirrus contributes around 81 ± 31% of the combustion climate impacts for LH, compared to 32 ± 7% for conventional jet fuel, showing that research is needed to reduce uncertainty in the case of LH. The life cycle impacts of the two dominant commercial LH pathways are on average 8 and 121% larger than conventional jet fuel. Some novel LH pathways do show considerable potential for life cycle climate impact reductions versus conventional fuel (up to -205 ± 78%). LH from renewable energy is not climate neutral, though, at best -67 ± 10% compared to conventional over the life cycle.