Large-scale adoption of clean hydrogen could have significant consequences for the climate due to the relative ease with which the H2 molecule — about eight times smaller than a methane molecule — can leak, according to a new study by US non-profit Environmental Defense Fund (EDF).

“Billions [of US dollars) in new investments and financial subsidies are being proposed to speed [the] adoption [of clean hydrogen]. Nevertheless, hydrogen itself has significant climate impacts that are both widely overlooked and underestimated, and it is a very small molecule that can easily leak into the atmosphere from infrastructure,” EDF scientists Ilissa Ocko and Steven Hamburg write in a peer-reviewed paper, Climate consequences of hydrogen emissions, published in the journal Atmospheric Chemistry and Physics.

According to a recent report by the UK government, hydrogen is about 11 times more powerful a greenhouse gas than CO2 over a 100-year period — or 33 times more powerful over 20 years. This is because H2 reacts with other greenhouse gases in the atmosphere to increase their global warming potential (GWP).

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“In this study, we evaluate the climate consequences, across all timescales, of deploying clean hydrogen given a range of plausible leak rates,” the EDF study explains. “Our results indicate that hydrogen emissions can considerably undermine the climate benefits of decarbonization strategies that involve clean hydrogen — especially in the decades immediately following deployment.

“Therefore, this issue deserves more attention, both with respect to advancing the science of hydrogen's indirect climate effects and regarding the improvement of estimates of hydrogen emissions throughout the value chain.

“Minimizing leakage will be essential to the effectiveness of hydrogen as a climate change mitigation strategy.”

The report explains that “hydrogen is a small molecule known to easily leak into the atmosphere, and the total amount of emissions (eg, leakage, venting, and purging) from existing hydrogen systems is unknown”.

But it estimates that average H2 leakage of 1% would be a “best-case scenario”, but it could be as high as 10% in some use cases.

“Green hydrogen applications with higher-end emission rates (10 %) may only cut climate impacts from fossil fuel technologies in half over the first two decades, which is far from the common perception that green hydrogen energy systems are climate neutral,” the study says.

“However, over a 100-year period, climate impacts [from fossil fuel technologies] could be reduced by around 80 %. On the other hand, lower-end emissions (1 %) could yield limited impacts on the climate over all timescales.”

It explains that an average leak rate of 1% would only add about 0.025°C to global warming by 2050, but 5% or 10% leakage could increase average worldwide temperatures by more than 0.1°C or 0.4°C, respectively.

Getting ahead of the problem

The EDF study explains that it would be easier to reduce hydrogen leakage when designing a new system, rather than retrofitting an existing one.

However, retrofitting existing natural-gas pipelines is far cheaper than building new hydrogen pipes. According to a recent study by the International Renewable Energy Agency, about one eighth of the world’s hydrogen — about 77 million tonnes annually — would be transported via retrofitted gas pipes by mid-century, in its 1.5°C scenario.

“We have the rare opportunity to get ahead of this issue before the infrastructure and systems are widely deployed,” Ocko and Hamburg write.

Their study recommends that five “key actions” should be taken to “help minimize hydrogen's warming effects and, therefore, maximize climate benefits in a future hydrogen economy”:

1) Advancing research into hydrogen's “indirect radiative effects and temperature responses to hydrogen emissions by incorporating interactive emissions, chemistry, and radiation parametrizations [ie, approximating complex processes] in further coupled chemistry-climate models as well as reduced-complexity climate models”;

2) Employing climate metrics that adopt not just a 20-year or 100-year time frame, but incorporate both, to reflect the role that hydrogen could play in meeting different net-zero goals;

3) Improving quantification of hydrogen leakage rates by developing technologies that can be used in the field to “accurately measure hydrogen emissions at low detection thresholds” — ie, as small as one part per billion;

4) Including “the likelihood of hydrogen leakage and its impacts in decision-making about where and how to effectively deploy hydrogen — such as co-located production and end-use applications”;

5) Identifying “leakage mitigation measures and best practices before building out infrastructure”.

The study continues: “If we are to meet the climate challenge before us, it is imperative that we carefully examine each alternative decarbonization pathway using robust and appropriate metrics and data.”

The short and medium-term climate impacts of hydrogen emissions “are higher than widely perceived”, it notes.

“These impacts should be explicitly and quantitatively accounted for in order to maximize the climate benefits of replacing fossil fuel systems with hydrogen.

“Taking a proactive and scientific approach to understand the implications of and address hydrogen leakage can help ensure that the global rush to hydrogen delivers on its promise to benefit the climate over all timescales.”

The full EDF study can be read here.

CORRECTION: The original headline for this article incorrectly stated that hydrogen leakage could reduce the climate benefits of green H2 by 80%. This was an error.