Redefining the Hydrogen “Colours” based on Carbon Dioxide Emissions: A New Evidence-Based Colour Code

This paper redefines hydrogen colour codes based on carbon dioxide emissions. It highlights that there are several colour codes, which disregard the carbon dioxide emitted in the hydrogen production process (e.g., electrolysis with renewable energy, steam reforming of natural gas, coal gasification, etc.). Some colours are used interchangeably for different technologies, while many colour codes do not assign a colour for all possible production pathways. Therefore, the existent framework is misleading and lacks scientific underpinning of colour labelling (e.g., green, blue, grey, black, yellow, purple, turquoise, etc.). This paper builds upon the work of Nikolaidis and Poullikkas and provides a qualitative assessment of the colour codes used to label various technologies. Based on a comparative analysis of the latest research and analysing hydrogen colour codes, this paper inquires whether there is or not, a common understanding of the hydrogen production pathways that lie behind each hydrogen “colour”. This paper finds that there are major inconsistencies regarding the colours used, especially for technologies using fossil fuels as an energy source, but nuclear energy has also been found to have discrepancies in labelling. At the same time, there is only one colour used to describe a wide range of technologies using renewable energy (i.e., green). However, if carbon dioxide emissions of the corresponding production technology were visually represented using a predefined colour-code, the hydrogen produced with fossil fuels would have a less diverse colour range, than current colour palettes would suggest. Rather than being “grey” and “blue”, coal, oil and gasbased hydrogen appear to be different shades of “brown” and “black”. This finding illustrates that these technologies emit more carbon dioxide emissions than an initial labelling would suggest, which raises the question whether any colours of hydrogen, other than its “green” versions, is compliant with the objectives of the Paris Agreement.