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

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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)