Hydrogen is widely seen as a key tool for cutting carbon emissions in industries that cannot easily switch to electricity, but a new scientific review warns that leaks at any point in the supply chain could significantly reduce or eliminate its climate benefits.
The review, published in Nature Reviews Earth and Environment, was led by CICERO researcher Maria Sand and involved scientists from institutions in Norway, the United States, France, the United Kingdom, and others. It examined what happens to hydrogen when it escapes into the atmosphere and how that affects the climate.
Hydrogen itself is not a greenhouse gas. But when it leaks into the atmosphere, it triggers chemical reactions that increase concentrations of other greenhouse gases, including methane, ozone, and stratospheric water vapor. All of those changes drive warming.
The review found that estimates of hydrogen's 100-year global warming potential are now converging on around 12 times that of CO2. According to the authors, those estimates are now solid enough to be used in policy and business decisions.
"Hydrogen can support the decarbonization of industry, transport and power, but the climate benefit depends on keeping hydrogen losses to the atmosphere as low as possible," said Sand, the review's lead author.
For a long time, hydrogen was treated as environmentally harmless. That assumption is changing. "Hydrogen has largely been considered environmentally benign. But as the science evolves and it is acknowledged that hydrogen has a global warming potential, including hydrogen's climate impacts in assessments and climate accounting frameworks is key as hydrogen deployment scales up," Sand noted.
The review was part of the CICERO-led HYway project. Hydrogen can leak at every stage of what researchers call the value chain, from production and storage to transport and end use. Natural sources also contribute hydrogen to the atmosphere, which complicates efforts to measure and regulate emissions from human activity.
Several scientific gaps remain. The review identified three areas needing more research. Scientists need better tools for measuring hydrogen emissions across the full supply chain. They also need a clearer picture of how soil absorbs hydrogen from the atmosphere, since soil acts as a natural sink that removes some emissions. Finally, climate models need to more completely represent how hydrogen interacts with atmospheric chemistry.
The review's findings arrive as governments and industries worldwide are scaling up hydrogen infrastructure and investment. The authors say that without tighter emissions controls and better monitoring, the climate case for hydrogen could weaken considerably.