A study led by researchers at the University of Sheffield has found that a global push for green hydrogen could fail to deliver intended climate benefits unless the ways hydrogen is produced and transported are overhauled. The paper, published in Nature Communications Sustainability, analysed how the environmental impact of hydrogen varies according to energy sources used across the supply chain. The authors warn that reliance on electricity from fossil fuel-based power systems can undermine the climate advantage of hydrogen. The researchers assessed 20 potential hydrogen production and transport scenarios across 14 countries between 2023 and 2050 and evaluated five hydrogen production pathways, including electrolysis and biomass-based processes. The analysis examined how energy sources and transport systems affect environmental outcomes and found that hydrogen produced by electrolysis currently gives some of the highest global warming impacts because much of the electricity used in the process still comes from carbon-intensive grids. At present around 96 per cent of global hydrogen production remains connected to fossil fuel-powered energy systems, which raises concerns about whether large-scale hydrogen deployment will automatically reduce emissions. The study also finds that hydrogen could become substantially cleaner if electricity systems are rapidly decarbonised, with some supply chains able to reduce environmental impacts by more than 90 per cent by 2050 compared with current production levels. Researchers identified scenarios in which international supply chains improve sustainability, notably where hydrogen produced in the United Kingdom using proton exchange membrane electrolysis is transported to the United States, subject to both countries transitioning to cleaner power systems. These results underscore the conditional nature of hydrogen benefits. The authors contend that realising the potential of hydrogen requires major changes to electricity systems, transport infrastructure and policy frameworks so that renewable electricity becomes dominant across supply chains. They recommend coordinated investment and regulatory action to align hydrogen deployment with rapid grid decarbonisation and careful planning of international trade routes. Without such systemic change the advantages of green hydrogen risk being negated by embedded fossil fuel emissions.