The hidden carbon cost of our world's most versatile fuel

Nature · Published 9 October 2026 Swipe more like this →

In short: Hydrogen is often hailed as a clean energy miracle, but the reality is more complex. While it can be produced from water using renewable power, nearly all of our current supply comes from fossil fuels, creating a significant carbon footprint that complicates its role in a green future.

Most of the world's current hydrogen supply is 'gray hydrogen,' produced via steam methane reforming (SMR). In this process, natural gas (methane) reacts with steam at temperatures between 700–1,100 °C over a nickel catalyst. While it is the cheapest industrial source—accounting for nearly 50% of global production—it is carbon-intensive, emitting between 6.6 and 9.3 tonnes of carbon dioxide for every single tonne of hydrogen produced.

To move toward a lower-carbon profile, the industry distinguishes between several 'colors.' Blue hydrogen is produced from fossil fuels but includes carbon capture and storage. Green hydrogen is produced by splitting water molecules into hydrogen and oxygen using renewable electricity (electrolysis). Other emerging methods include turquoise hydrogen (methane pyrolysis without CO2 emissions), brown or black hydrogen (from coal), and biological production using microbes like bacteria or algae.

The transition to green hydrogen faces significant hurdles in efficiency and cost. Current water electrolysis typically operates at 70–80% electrical efficiency, requiring 50–55 kWh of electricity to produce 1 kg of hydrogen. While electrolysis costs are falling—currently ranging from $3 to $8/kg—the US Department of Energy has set a 'Hydrogen Shot' goal to reach $1/kg by 2031 to compete with the $1.50/kg price of natural gas-derived hydrogen.

Technological diversity is key to scaling. Solid oxide electrolyser cells (SOECs) can utilize high-temperature heat from industrial waste or nuclear power to reduce electricity needs, while polymer electrolyte membrane (PEM) cells are ideal for variable solar inputs. Even a 2022 study on capillary-fed electrolysis cells showed a potential 98% energy efficiency, highlighting the ongoing engineering push to make hydrogen a viable global commodity.

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