The method used to produce hydrogen has an impact on its carbon (and environmental) footprint. Most existing large-scale production relies on fossil fuels, resulting in greenhouse gas (GHG) emissions. The key methods for producing hydrogen are:

Steam methane reforming

(SMR) produces hydrogen and CO2 from methane via high temperature processing. SMR accounts for around half of global hydrogen production.

Natural gas is the most cost effective source of methane, but energy is lost in the process so natural gas demand could increase if hydrogen from SMR were to replace natural gas for heating.

If exploited without carbon capture, usage and storage (CCUS) then this would be more carbon intensive than the direct burning of natural gas, but with CCUS estimates say between 80%-90% of the carbon emissions can be captured (resulting in what is called blue hydrogen).

Gasification

Gasification converts organic material to hydrogen through a multi-step process. Gasification of coal accounts for roughly 18% of global hydrogen production, although a small number of plants have begun using biomass as a lower carbon alternative.

Gasification using biomass has an estimated carbon footprint around half that of natural gas and with CCUS it can have negative carbon emissions.

Electrolysis

Electrolysis (known as green hydrogen) uses electricity to separate water into oxygen and hydrogen. It is estimated to account for 4% of global production.

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How is hydrogen made?

Steam methane reforming

Gasification

Electrolysis