SMR: Steam methane reforming
Grid electricity
Electrolysis
Green H₂
0 – 50
Renewables
Electrolysis
Green H₂
0 – 0.5
CCS
Blue H₂
0.5 – 8.8
Natural gas
Reforming
(SMR/ATR)
Grey H₂
9.8 – 13
Coal
Coal gasification
Brown H₂
20 – 25
Hydrogen colours:
carbon intensity (kgCO₂eq/kgH₂)