National hydrogen policy inequality in aviation: a hidden barrier to climate mitigation

As the aviation industry seeks to reduce its climate impact, hydrogen has emerged as a promising alternative to conventional jet fuels due to its potential for zero carbon dioxide emissions and reduced non-CO₂ effects. However, beyond well-known technological, economic, and infrastructural obstacles, the global transition to hydrogen-powered aviation faces the lack of alignment of national policy frameworks as an overlooked barrier. Quantifying the inequality of national policy frameworks is raised as a critical question. This study directly addresses this gap by proposing a novel composite index – the Hydrogen Aviation Policy Index (HAPI)- to assess the policy readiness of 221 countries and territories to promote hydrogen in aviation. HAPI is constructed through min–max normalization, heuristic weighting, and multi-way interaction terms that enable cross-national comparisons. Results reveal significant policy inequality across the globe. While the Global North shows substantial inequality, the Global South exhibits what we term ‘neutral uniformity’ – most countries have near-zero HAPI scores, reflecting uniform policy inaction rather than equitable progress. Norway and the United Kingdom emerge as leaders in promoting hydrogen aviation, whereas the United States ranks as the worst-performing country due to its low policy engagement relative to its share of aviation emissions and market. Accordingly, there is no meaningful correlation between HAPI scores and national aviation emissions, suggesting a clear disconnect between climate responsibility and policy action. Sensitivity and cluster analyses confirm the index’s robustness and highlight structural divergence among nations. These findings indicate that inequality in national hydrogen aviation policies represents a significant barrier to climate mitigation.