Hydrogen is considered an important component of the energy transition. But the supposedly climate-neutral energy source also indirectly promotes global warming: it delays the breakdown of the greenhouse gas methane in the atmosphere and also influences cloud formation. A study has now quantified hydrogen emissions and sinks since 1990. Important sources are therefore the decay of methane and – to a much lesser extent – leaks during hydrogen production. The results help to assess the environmental benefits of hydrogen in a more differentiated manner and to minimize negative effects.
Methane (CH4) escapes from natural gas pipelines, cattle stomachs and landfills and acts as a greenhouse gas many times more powerful than carbon dioxide. Within 20 years of its release, it contributes 80 times more to global warming than CO2. But other than this, it does not remain in the atmosphere for centuries, but is usually broken down within about ten to twelve years. The most important mechanism is the reaction with free hydroxyl radicals (OH) in the atmosphere, whereby CH4 and OH become water and carbon dioxide in several steps. Hydrogen (H2) is also produced as an intermediate and by-product. But this competes with methane for the OH radicals. “More hydrogen means less OH in the atmosphere, which means methane persists longer and therefore warms the climate for longer,” explains Zutao Ouyang from Stanford University in California.
Climate helpers with risks
Together with his team, Ouyang has now analyzed for the period from 1990 to 2020 from which sources how much hydrogen is released and which hydrogen sinks remove this gas from the atmosphere. “We need a deeper understanding of the global hydrogen cycle and its connections to global warming to support a climate-proof and sustainable hydrogen economy,” says Ouyang’s colleague Robert Jackson. Since hydrogen does not release CO2 when burned, only water, it is considered a climate-neutral energy source. As part of the energy transition, it should increasingly replace fossil fuels.
But hydrogen also poses climate risks. “Hydrogen is the smallest molecule in the world and easily escapes from pipelines, production facilities and storage facilities,” explains Jackson. Although H2 itself does not store heat in the atmosphere, its interactions with other gases contribute 37 times more to warming than CO2 within the first 20 years after its release. It causes eleven times more warming within 100 years. “The best way to reduce warming from hydrogen is to prevent leaks and reduce emissions of methane, which breaks down into hydrogen in the atmosphere,” says Jackson.
Increased release and absorption
The analysis of H2 sources and sinks shows that human activities play an important role in the release of hydrogen: “H2 sources increased from 1990 to 2020, primarily due to the oxidation of methane and other anthropogenic volatile organic compounds, biogenic nitrogen fixation, and leaks in H2 production,” the research team reports. Emissions from burning fossil fuels and forest fires also play a role. In total, an average of 69.9 million tons of hydrogen were released into the atmosphere each year from these sources between 2010 and 2020.
As the H2 concentration increased, the H2 sinks also absorbed more hydrogen. “The most important way hydrogen is removed from the atmosphere worldwide is through microbes in the soil that use H2 to generate energy,” explain the researchers. In this way alone, 50 million tons of hydrogen are removed from the atmosphere every year. In addition, there is degradation using OH radicals in the atmosphere, which accounts for 18.4 million tons per year.
contribution to global warming
The remaining gap between the release and degradation of 1.55 million tonnes of hydrogen per year ensures that the atmospheric content of the gas increases, slows down the breakdown of methane and indirectly further warms the climate. There are also interactions with ozone and an influence on cloud formation. “We estimate that the increase in atmospheric H2 contributed to a 0.02 degree Celsius increase in global surface air temperature between 2010 and 2020,” the team said.
According to Ouyang and his colleagues, how the climate impact of hydrogen develops in the future depends on numerous factors, including the production methods, the transport and storage infrastructure and the areas of application. In order for H2 to actually develop its full benefits for the climate and offer a sustainable alternative to fossil fuels, it is important to be aware of the potential risks and minimize them.
Source: Zutao Ouyang (Stanford University, California, USA) et al., Nature, doi: 10.1038/s41586-025-09806-1