The context of this research is the urgent global climate challenge of preventing a global mean surface temperature increase of more than 1.5 C compared to the pre-industrial average, defined as 1850-1900. The IPCC (2021) has warned of serious consequences to human health and societies of such a rise in global temperature. We are already 80% of the way to this threshold: the global mean surface temperature for 2016-2020 the was about 1.2 C about the pre-industrial average (Morice et al 2021, Met Office 2021).

In the UK, road transport has reduced its carbon footprint less than other sectors since 1990, and larger vehicles are particularly problematic to decarbonise due to the huge infrastructure requirements for electrification, and the limited range of battery traction. Hydrogen fuel cells are a possible solution to power larger road vehicles cleanly, as outlined in the Hydrogen Strategy of the UK Government (2021). However, about 95% of hydrogen is currently produced by steam methane reforming, which has significant carbon emissions even when carbon capture is implemented (Howarth and Jacobson 2021). Most research on the environmental impacts of hydrogen production, storage and delivery has focused on a narrow subset of hydrogen technology or a narrow range of environmental indicators (often just global warming potential and acidification) - need for a comprehensive comparison. There is also a need to consider the intersections between decisions made for road transport and competing uses of hydrogen for ammonia production and industrial processes, and domestic heating and cooking.

My planned research is intended to fill gaps highlighted by recent studies (Cluzel et al. 2021, Howarth and Jacobson 2021, Ren and Toniolo 2018, Campos-Guzmán et al. 2019, Ji and Wang 2021). In summary, identifying a sustainable decarbonisation pathway will require:

* consideration and inclusion of a broad range of new hydrogen technologies as they mature;

* inclusion of a wide range of environmental indicators;

* real-world performance data rather than simulated or modelled data where possible, with analysis of purification requirements and minimising fugitive greenhouse gas emissions;

* consequential LCA with an integrated tool to assist decision makers, such as multi-criteria decision making (MCDM), which considers competing uses of hydrogen in its analysis.

My research project will produce as its outputs: a review of recent Life Cycle Assessments (LCAs) of hydrogen; a review of the most promising hydrogen technologies; a detailed consequential LCA of hydrogen production, storage and delivery (cradle to station); and an online, user-friendly decision support tool that shows costs and benefits (financial and environmental) for a range of hydrogen pathways under user-selected economic and technological scenarios.

Researchers, government officials and other interested parties will have access to a decision support tool that they can customise for their country or organisation to find a pathway that provides hydrogen for transport with a minimised carbon footprint and other environmental impacts. Researchers will have full access to all the underlying data, research and methodologies, to further their research. It will also be possible for researchers to update the support tool with the latest data and calculations for a specific component of the LCA inventory, or a specific locale.