Hydrogen holds promise as an alternative energy source that will play an important role in decarbonizing the global energy system, potentially fueling our industrial production, homes, commerce and infrastructure one day.

However, scientists warn there is reason to be cautiously optimistic. Hydrogen (H₂) interacts with methane, ozone (pollution) and water vapor in the atmosphere in ways that may warm the climate, thereby potentially negating its benefits.

A new study co-led by an Auburn University researcher and published in the esteemed scientific journal, Nature, suggests embracing a "hydrogen economy" will require a deeper scientific understanding of the global hydrogen cycle to support a climate-safe, sustainable hydrogen economy.

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 approximately 37 times faster during the first 20 years.

Unintended consequences

"This indirect warming raises concerns about the climate consequences of potential hydrogen leakage, and highlights that the climate benefits of a future hydrogen economy will depend on minimizing leakage through the hydrogen value chain and reducing natural gas (methane) emissions," said Zutao Ouyang, leading author of the study and assistant professor of ecosystem modeling in Auburn's College of Forestry, Wildlife and Environment (CFWE).

To assess the impact of this leakage, Ouyang worked with an international consortium of scientists known as the Global Carbon Project, to develop the first comprehensive accounting of global hydrogen sources and sinks to assess changes in atmospheric hydrogen and its climate consequences.

The study, "The Global hydrogen budget," published today, is co-led by Ouyang and Rob Jackson, Stanford University professor and chair of the Global Carbon Project, in collaboration with researchers from approximately 30 international institutions from France, Australia, China, Japan, United Kingdom, Norway and Austria.

"The team collected direct measurements of hydrogen in the atmosphere, along with the most comprehensive ever data collection and modeling to estimate the major sources and sinks of hydrogen and produce a first-of-its-kind global picture," said Pep Canadell, the executive director of Global Carbon Project, and chief research scientist at CSIRO Environment, Australia.

After, they projected future hydrogen emissions, removals and atmospheric levels under different scenarios of the Intergovernmental Panel on Climate Change (IPCC), using a simplified Earth system model to estimate how these changes could affect the climate.

Since hydrogen production began to increase 30 years ago, the researchers estimate hydrogen concentrations in the atmosphere increased by about 70% from preindustrial times through 2003, then briefly stabilized before picking up again around 2010. The authors found this increase is largely due to leakage from increased hydrogen production and, surprisingly and less known, due to the formation of hydrogen that results from the oxidation of increasing methane emissions from human activities.

Methane (CH₄) emissions — especially from fossil fuel extraction, distribution and use — have an important, but often under-appreciated, influence on atmospheric hydrogen. Methane and hydrogen share the same pathway by which they are cleaned (oxidized) in the atmosphere, and because methane oxidation itself produces hydrogen, this creates feedback that can raise atmospheric hydrogen concentrations when methane emissions increase; further competing for the detergent that cleans the atmosphere from methane.

Though the overall climate effects are relatively small currently, these complex interactions have the potential to undermine the positive effects of hydrogen.

Calculating the risks

"The largest source of hydrogen in the world is the oxidation of methane in our atmosphere," Jackson said. "But methane and hydrogen also compete for atmospheric cleansing detergents. This competition extends methane's lifecycle in the presence of hydrogen, thereby increasing indirect climate warming. More hydrogen means more methane, and more methane means more hydrogen."

The authors agree, if a hydrogen economy is to become widely accepted, the unintended warming driven interactions between hydrogen and methane must be reduced to build trust in hydrogen as a viable decarbonization pathway.

"By quantifying the previously unaccounted warming feedback between hydrogen and methane that are missing in current climate projections, we hope to improve future climate scenarios and support decision-makers in minimizing both economic losses and climate risks associated with hydrogen leakage," Ouyang said.

Driving solutions

With this research in hand, policymakers, industries and researchers are equipped with the quantitative evidence needed to set safe hydrogen and methane leakage thresholds, craft effective regulations and prioritize cost-efficient mitigation strategies.

"The significance of this international study cannot be overstated," said Janaki Alavalapati, the Emmett F. Thompson Dean of the CFWE. "The team's comprehensive assessment of hydrogen sources and sinks, and their associated warming impacts, can help ensure that the global expansion of hydrogen aligns with a climate-safe and sustainable energy transition."

The research study was funded by the Gordon and Betty Moore Foundation, Stanford Doerr School of Sustainability, Stanford's Global Methane Office and Auburn's CFWE.

Auburn University is a nationally ranked land grant institution recognized for its commitment to world-class scholarship, interdisciplinary research with an elite, top-tier Carnegie R1 classification, life-changing outreach with Carnegie's Community Engagement designation and an undergraduate education experience second to none. Auburn is home to more than 30,000 students, and its faculty and research partners collaborate to develop and deliver meaningful scholarship, science and technology-based advancements that meet pressing regional, national and global needs. Auburn's commitment to active student engagement, professional success and public/private partnership drives a growing reputation for outreach and extension that delivers broad economic, health and societal impact.

SOURCE Auburn University