Hydrogen has increasingly been cited as playing a key role in helping to tackle climate change, but the nature and potential of this natural fuel is perhaps not as clear cut as many have hoped.
As H2 only releases water vapour when burned, it has been suggested as an important element of the toolkit to help decarbonise industries from transport to steel and chemical production and increase many countries' energy independence.
But, adding to existing doubts about how clean some hydrogen production methods actually are, two new reports commissioned by the UK government have highlighted the importance of minimising hydrogen leakage, as the gas could be a greater indirect contributor to global warming than was previously thought.
While burning green hydrogen creates relatively clean energy, the gas in its natural form can act as an “indirect greenhouse gas” as it reacts with other gases in the atmosphere to increase what’s called their global warming potential (GWP).
EXPLAINER: Green hydrogen versus blue hydrogen (and turquoise and grey hydrogen)
Hydrogen is twice as powerful a greenhouse gas as previously thought, according to the first study, which commissioned by the Department of Business, Energy and Industrial Strategy (BEIS) and used the latest climate and atmospheric chemistry models to explore the atmospheric impacts of a global hydrogen economy.
Hydrogen’s GWP is between six and 16 times more than carbon dioxide, which has a GWP of one.
Its GWP had previously been thought to be 5.8, based on a study from 2001.
The 75-page report, entitled Atmospheric Implications of Increased Hydrogen Use, was the result of academics from the University of Cambridge, National Centre for Atmospheric Science and University of Reading modelling the atmospheric impact from hydrogen emissions to calculate hydrogen’s global warming potential.
They noted that hydrogen-induced changes in methane and ozone have previously only been considered in the lowest layer of the atmosphere, the troposphere.
The academics said they considered the “previously ignored” changes in the next level up, the stratosphere, along with water vapour and stratospheric ozone.
For the 20-year time horizon, on the way to the UK government’s target to get to net zero by 2050, the report suggested hydrogen has a GWP of 33, with an uncertainty range of 20 to 44.
The report recommends that “hydrogen leakage be reduced and that consideration be given to how hydrogen is used to minimise the atmospheric impacts of energy use”.
The second BEIS report, Fugitive Hydrogen Emissions in a Future Hydrogen Economy, said there are “likely to be hydrogen emissions across the hydrogen landscape from production, transport, and storage through to end-use applications.
“Technologies can be implemented to reduce the key emissions from production (electrolysis) and end-users (fuel cells).
“If these are widely adopted the dominant emission source is likely to be a gas distribution network repurposed to transport 100% hydrogen.”