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Monday, August 16, 2021 

A paper published in the journal 'Energy Science & Engineering' by Robert W. Howarth of Cornell University, US, and Mark Z. Jacobson, Stanford University, US has examined the role of 'blue' hydrogen in decarbonisation, looking at the lifecycle greenhouse gas emissions (GHG) of blue hydrogen accounting for emissions of both carbon dioxide (CO2) and unburned fugitive methane.

The authors say that hydrogen is often viewed as an important energy carrier in a future decarbonised world. Currently, most hydrogen, so called 'grey' hydrogen, is produced by steam reforming of methane in natural gas, with high CO2 emissions. Increasingly, many propose using carbon capture and storage to reduce these emissions, producing so-called 'blue' hydrogen, frequently promoted as low emission fuel.

The paper concludes that, far from being low carbon, GHG emissions from the production of blue hydrogen are relatively high, due in particular to the release of fugitive methane.

Using a default assumption (3.5% emission rate of methane from natural gas and a 20-year global warming potential), total CO2 equivalent emissions for blue hydrogen are only 9%-12% less than for grey hydrogen. While CO2 emissions are lower, fugitive methane emissions for blue hydrogen are higher than for grey hydrogen because of an increased use of natural gas to power the carbon capture. Perhaps surprisingly, the GHG footprint of blue hydrogen is more than 20% greater than burning natural gas or coal and some 60% greater than burning diesel oil, again using the default assumptions. Even in a sensitivity analysis in which the methane emission rate from natural gas is reduced to a low value of 1.54%, GHG emissions from blue hydrogen are still greater than from simply burning natural gas, and are only 18%-25% less than for grey hydrogen. The analysis assumes that captured CO2 can be stored indefinitely, an optimistic and unproven assumption. Even if true though, the use of blue hydrogen appears difficult to justify on climate grounds.

The best-case scenario for producing blue hydrogen, using renewable electricity instead of natural gas to power the processes, suggests that there really is no role for blue hydrogen in a carbon-free future. GHG emissions remain high, and there would be a substantial consumption of renewable electricity, which represents an opportunity cost. The authors believe the renewable electricity could be better used by society in other ways to replace the use of fossil fuels. Similarly, they see no advantage in using blue hydrogen powered by natural gas compared with simply using the natural gas directly.

The paper concludes that blue hydrogen is best viewed as a distraction, something than may delay needed action to truly decarbonise the global economy.

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