The answer is probably, a classic: "it depends". Hydrogen is the smallest and lightest molecule in the world. It is about eight times lighter than methane. There's a lot of methane leakage around the world. And by "a lot", I really mean a lot. Satellite imagery by the European Space Agency collected data that proves there is significantly more leakage in the atmosphere than official estimates. And methane has more than 80 times the warming power of carbon dioxide over the first 20 years after it reaches the atmosphere (Source: Environmental Defense Fund - EDF). Some of this methane leakage is due to sheer industry negligence (oil and gas companies have been proven to do routine gas flaring), but also to bad casings, old pipes, and all sorts of infrastructure mishaps that are bound to happen in any industry. Now imagine how much easier is for hydrogen - a much lighter molecule than methane - to escape and leak, particularly when we blend it with natural gas in existing pipelines, as is the case in the plans of many countries in Europe - including Romania, my home country.
What's the scientific evidence to date of the potential environmental consequences of methane leakage? EDF lab studies have shown that hydrogen leakage is, in the best case, around 1% but could go up to as much as 10%. And a 10% leak could lead to 0.1°C or 0.4°C increases, the scientists claim. And this is because hydrogen has an indirect global warming effect by extending the lifetime of other GHGs (Fan et al., 2022). UK-based scientific evidence brings about even more worrisome figures: hydrogen may have a 100-year global warming potential of about 11 times greater than carbon dioxide (Warwick et al., 2022). Compared to the warming it is trying to abate by displacing fossil fuels, it turns out that in a high leakage scenario, "hydrogen emissions could yield nearly twice as much warming in the first five years after replacing its fossil fuel counterparts." On the other hand, if leaks are minimal, the climate benefits are consistent - an 80% decrease in warming compared to fossil fuels over the same period of time. The danger is real, it seems, even in the case of green hydrogen, let alone in the case of blue hydrogen, where the combo between methane leaks and hydrogen leaks could be a truly deadly cocktail for the planet.
Leakage is assumed to be lowest in industrial on-site usage and highest in the production process, followed by transportation and delivery, while not enough data is available for the end-use leakage. Specialists believe that measures such as designing new hydrogen infrastructure with a focus on leakage prevention and penalising leakage where it does occur, alongside focusing on incentivizing hydrogen in so-called "hubs" (industrial sites where it is both produced and consumed), to the detriment of decentralized usage (e.g., in heating and transportation), can still keep hydrogen a climate ally rather than a climate foe (Koch Blank et al., 2022).
Research on these topics is still in its infancy, with most of the peer-reviewed reports released in 2022. It is clear that intense further research is needed on leakage risks, mitigation strategies, and warming effects. At the same time, however, as the "hydrogen rush" is already moving ahead at full speed in the EU, it's probably worth introducing strong safeguards from the very beginning, in parallel to the advance of sciences:
prioritise green over any other colour of hydrogen
prioritise hydrogen in sectors where it can be easily produced and consumed onsite (and which are hard to decarbonize to start with, like the fertilizer industry or steel production) and deploy hydrogen at scale in other sectors (e.g.: transportation, heating) later. This probably makes sense from a basic business planning perspective, too.
create new infrastructure for hydrogen, and don't retrofit old pipes that leak.
put in place the highest level industry standards for leakage prevention
unlike methane, where many jurisdictions are still not taxing leakage with hydrogen; let's not repeat the mistakes of the past, and let's design a leakage penalty system from the very beginning.
References:
Ilissa B. Ocko and Steven P. Hamburg, Environmental Defense Fund (EDF), 2022, “Climate consequences of hydrogen emissions”, in Atmos. Chem. Phys., 22, 9349–9368, 2022, https://doi.org/10.5194/acp-22-9349-2022
Fan, Z., et al, 2022, “Hydrogen Leakage: A Potential Risk for the Hydrogen Economy”, Columbia, SIPA, Center on Global Energy Policy, available at https://www.energypolicy.columbia.edu/sites/default/files/pictures/Hydrogen%20Leakage%20Regulations,%20designed,%207.21.22.pdf
Koch Blank T. et al., 2022, “Hydrogen Reality Check #1: Hydrogen Is Not a Significant Warming Risk”, available at https://rmi.org/hydrogen-reality-check-1-hydrogen-is-not-a-significant-warming-risk/