The hydrogen-to-carbon mole perspective reveals cleanness and inequality of global and national fossil fuel transition

Transition away from fossil fuels concerns both carbon and hydrogen as the main energy carriers in different hydrocarbons, but the current energy transition literature primarily emphasizes carbon, with limited attention to hydrogen embedded in fossil fuels. Here we introduce the index of Hydrogen-to-Carbon Mole Ratio (HCR) to measure the clean transition and inequality of global and national fossil fuel consumption, production, export, and import over nearly four decades (1980-2016). We show that the HCR reveals the cleanness of fossil fuel consumption and production falling behind those of import and export. Energy transition demonstrates inequality, as high and upper-middle income economies continuously consume cleaner fossil fuels with higher HCR than the lower-middle and low income economies. Despite higher per capita mole consumption, high-income economies require less hydrogen and carbon intensity than low income economies to sustain economic growth. Metrics based on the molecular HCR can be extended to long-term energy transition beyond fossil fuel, and help monitor the transition, inequality, and decarbonization strategies in human energy systems. Song, Liu, and colleagues introduced a Hydrogen-to-Carbon Mole Ratio (HCR) index to measure the cleanness of global fossil fuel transition over nearly four decades, and found that high-income economies use cleaner fossil fuels (with higher HCR) than low-income ones, highlighting global energy inequality.