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