A new study led by researchers at the University of Sheffield warns that a global push toward green hydrogen could fail to deliver its intended climate benefits unless major changes are made to the way hydrogen is produced and transported. Published in Nature Communications Sustainability, the research finds that the environmental impact of hydrogen varies significantly depending on the energy sources used across the supply chain. The study emphasises that green hydrogen will not be inherently low carbon without cleaner power systems underlying production. The authors assessed 20 potential hydrogen production and transport scenarios across 14 countries between 2023 and 2050, including major hydrogen economies such as the United States, the United Kingdom, Germany, Japan and China. The analysis evaluated five hydrogen production pathways, including electrolysis and biomass-based processes, and examined how energy sources and transport systems affect environmental outcomes. It found that hydrogen produced through electrolysis currently has 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, raising doubts about whether large scale hydrogen deployment will automatically reduce emissions. The study projects that hydrogen could become significantly cleaner if electricity systems are rapidly decarbonised, with some supply chains capable of reducing environmental impacts by more than 90 per cent by 2050 if renewable electricity becomes dominant. The researchers also identify a potential role for international supply chains in improving sustainability. One scenario highlighted involves hydrogen produced in the United Kingdom using proton exchange membrane electrolysis and transported to the United States, which could achieve substantially lower environmental impacts provided both countries transition to cleaner power systems. The study concludes that policy makers and industry must coordinate rapid power sector decarbonisation and careful design of production and transport networks to realise the climate benefits of hydrogen. Without a comprehensive supply chain overhaul the green hydrogen push risks delivering limited emissions reductions.