What is grey – blue – green hydrogen?

To support the transport sector, and other hard-to-decarbonize industries, ensuring a low-carbon, clean hydrogen supply is essential. According to the World Energy Council, in its 2019 insights brief on New Hydrogen, the source of energy used and the production method define whether hydrogen is informally considered grey, blue or green; with the following definitions:

• Grey hydrogen - Currently, 96% of hydrogen is produced from fossil fuels via carbon intensive processes.
• Blue hydrogen - Grey hydrogen whose CO₂ emitted during production is sequestered via carbon capture and storage (CCS).
• Green hydrogen - Low or zero-emission hydrogen produced using clean energy sources.