Pathways to global hydrogen production within planetary boundaries

Hydrogen is a key lever for decarbonising hard-to-electrify sectors. Mitigation scenarios project an essential role for hydrogen in returning within the climate change planetary boundary. Yet, its planetary footprint remains unclear, particularly when Earth system interactions are considered. Here, we quantify the planetary footprint of global clean hydrogen production using a bottom-up system model coupled with an Earth system interaction model. From 2025 to 2050, even under the most favourable scenarios, global hydrogen production is likely unsustainable, confirming previous findings. We further show that Earth system interactions amplify hydrogen's planetary footprint. While electrolytic and abated fossil production are complementary, bio-based production is an order of magnitude more unsustainable, as opposed to current trends. Our results contrast with the current focus on "green hydrogen" which does not inform on its sustainability. Achieving sustainable hydrogen production will require the reconsideration of viable production pathways, starting with the decarbonisation of existing production capacity.