Overlooked hydrogen emissions are heating Earth and supercharging methane
By: Communications
Rising global emissions of hydrogen over the past three decades have amplified the impact of the greenhouse gas methane and intensified climate change - according to an international team including researchers at the University of East Anglia.
Hydrogen is often hailed as a clean energy solution. But a new paper published in the journal Nature reveals that atmospheric hydrogen (H₂) concentrations have risen steadily since 1990 - largely due to human activity.
Authored by an international consortium of scientists known as the Global Carbon Project, the study is one of the first comprehensive accounts of hydrogen sources and sinks.
The team say that the rise could pose a growing challenge for climate goals.
The new study has been led by climate scientists at Stanford and Auburn Universities in the US. Researchers from UEA’s School of Environmental Sciences focused on the role of both ocean fluxes and wildfires on hydrogen in the atmosphere.
“Hydrogen is the world’s smallest molecule, and it readily escapes from pipelines, production facilities, and storage sites,” said Stanford University scientist Prof Rob Jackson, senior author of the Nature paper and chair of the consortium. “The best way to reduce warming from hydrogen is to avoid leaks and reduce emissions of methane, which breaks down into hydrogen in the atmosphere.”
Amplifying methane
Unlike greenhouse gases including carbon dioxide and methane, hydrogen itself does not trap heat in Earth’s atmosphere.
Through interactions with other gases, however, hydrogen indirectly heats the atmosphere roughly 11 times faster than carbon dioxide during the first 100 years after release, and around 37 times faster during the first 20 years.
Prof Parvadha Suntharalingam, from UEA’s School of Environmental Sciences, said: “Atmospheric hydrogen is rising, and a major source is due to the atmospheric chemical breakdown of methane emissions and related compounds. These processes also lead to atmospheric chemical feedbacks that generate more hydrogen, thus amplifying its impact on climate.”
“This study highlights the value of a comprehensive accounting of the sources and sinks of atmospheric hydrogen, and how they have changed recently. Understanding these fluxes is essential because they influence atmospheric concentrations and, ultimately, the climate impact of hydrogen.”
Wildfires expert Dr Matt Jones, also from UEA’s School of Environmental Sciences, said: “Wildfires contribute a substantial share of H2 emissions, and their impact varies significantly among different periods with fire activity, and without a detectable trend. A possible future increase in wildfires under climate change would increase this contribution.”
Consuming natural detergents
The main way hydrogen contributes to global warming is by consuming natural detergents in the atmosphere that destroy methane.
“More hydrogen means fewer detergents in the atmosphere, causing methane to persist longer and, therefore, warm the climate longer,” said lead study author Zutao Ouyang, an assistant professor of ecosystem modeling at Auburn University, who began the work as a postdoctoral scholar in Prof Jackson’s lab in the Stanford Doerr School of Sustainability.
In addition to extending the heat-trapping life of methane, hydrogen’s reactions with nature’s detergents also produce greenhouse gases such as ozone and stratospheric water vapor, and affect cloud formation.
The researchers estimate hydrogen concentrations in the atmosphere increased by about 70 per cent from preindustrial times through 2003, then briefly stabilized before picking up again around 2010.
Between 1990 and 2020, hydrogen emissions increased mostly because of human activities, the authors found.
Vicious cycle
Major sources include the breakdown of chemical compounds including methane, which itself has been rapidly building up in the atmosphere because of growing emissions from fossil fuels, agriculture, and landfills.
Because methane breaks down into hydrogen in the atmosphere, more methane means more hydrogen. More hydrogen, in turn, means methane emissions stick around longer, doing more damage.
“The biggest driver of hydrogen increase in the atmosphere is the oxidation of increasing atmospheric methane,” said Prof Jackson.
Since 1990, the authors estimate the annual emissions from this source of hydrogen has grown by about 4 million tons, to 27 million tons per year in 2020. Other important hydrogen sources since 1990 include leakage from industrial hydrogen production and the process of nitrogen fixation, which farmers harness to grow legume crops like soybeans.
Natural sources of hydrogen, such as wildfires, varied from year to year without a consistent trend across the 1990-2020 period.
Future energy systems
The most detailed data in the study covers the decade ending in 2020, drawing on multiple datasets and models and incorporating emission factors for hydrogen and precursor gases such as methane and other volatile organic compounds.
The authors found 70 per cent of all hydrogen emissions were removed during this period by soil, largely through bacteria consuming hydrogen for energy.
Overall, the buildup of hydrogen in our atmosphere has contributed a fraction of a degree (0.02 degrees Celsius) to the nearly 1.5 degree Celsius increase in average global temperatures since the Industrial Revolution.
According to Ouyang, Jackson, and colleagues, this temperature increase from rising hydrogen concentrations is comparable to the warming effect of the cumulative emissions from an industrialized nation such as France.
Any contribution to warming could diminish the climate benefits of replacing fossil fuels with hydrogen, which has long garnered interest from some politicians, executives, and academics as a clean-burning alternative to oil and gas for heavy industry and transportation.
More than 90 per cent of hydrogen production today is enormously energy intensive. It’s derived mainly from coal gasification or steam methane reforming, which have large carbon footprints.
But because it’s possible in theory to produce hydrogen with renewable energy and close to zero carbon emissions, most scenarios for decarbonizing the world’s energy systems in the coming decades assume low carbon hydrogen production will dramatically increase.
“We need a deeper understanding of the global hydrogen cycle and its links to global warming to support a climate-safe and sustainable hydrogen economy,” said Prof Jackson.
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