Rising Atmospheric Hydrogen: A Potential Climate Concern

Hydrogen levels in the atmosphere have surged by 60% since the pre-industrial era, underscoring the significant influence of fossil fuel use on the Earth’s atmospheric makeup. While hydrogen itself isn’t a greenhouse gas, it contributes to warming indirectly through its interactions with other substances.

The research findings stem from the first comprehensive long-term observations of atmospheric hydrogen, which are derived from ice core data collected in Greenland in 2024. “Ice core records are incredible,” notes Alex Archibald from Cambridge University.

Being a small and lightweight molecule, hydrogen tends to escape into the atmosphere easily, often leaking from the ice core before it is analyzed in the lab.

To tackle this issue, John Patterson from the University of California, Irvine, and his team examined the ice core samples right after extraction. “We took our equipment out onto the ice. As soon as we extracted the samples, we cleaned and sealed them in a melted chamber for analysis,” he explains.

This approach enabled the researchers to establish a long-term record of atmospheric hydrogen stretching back 1,100 years, marking a significant improvement over previous records that reached only 100 years, largely based on observational data and snowfall analyses. “It’s quite an impressive feat logistically. We’re excited to share these findings,” remarks David Stevenson from the University of Edinburgh, UK.

The study discovered that hydrogen concentrations have risen from roughly 280 parts per billion in the early 19th century to around 530 parts per billion today. According to Patterson, this is not surprising given the rapid increase in fossil fuel usage since the pre-industrial period—when fossil fuels or biomass burn, hydrogen is released as a by-product.

Patterson and his team merged data from ice core records with modeling efforts to illustrate the fluctuations in hydrogen levels over the millennium. “Our data reveals changes in atmospheric composition, but the reasons behind these changes remain unclear,” says Patterson. “We aim to utilize biogeochemical models to investigate these variations.”

For instance, evidence from ice cores indicates that atmospheric hydrogen levels dipped by 16% during the so-called Little Ice Age, a cold period from the 16th to the 19th century. The decrease in wildfire emissions during this time does not completely account for the notable drop in hydrogen concentrations, according to Patterson. “This suggests that natural hydrogen biogeochemistry is adapting to climate change in ways we still don’t fully comprehend. This unexpected finding could be significant for future scenarios, indicating that atmospheric hydrogen levels might be more sensitive to climate fluctuations than previously believed,” Patterson cautions.

In the atmosphere, hydrogen competes with methane and engages with hydroxyl radicals, which play a crucial role in eliminating methane from the atmosphere, a potent greenhouse gas. “As hydrogen levels rise, the amount of hydroxyl available to react with methane decreases,” explains Patterson, potentially enhancing methane’s warming effect. “Currently, hydrogen constitutes about half of the total in the atmosphere, contributing approximately 2% to the overall anthropogenic warming effect according to our best estimates.”

Gaining a deeper understanding of the hydrogen cycle is essential to assess whether the widespread adoption of hydrogen fuels, as a transition away from fossil fuels, might lead to unanticipated consequences. For instance, a sudden spike in atmospheric hydrogen could magnify the warming impact of methane. Methane emissions have consistently risen since 2007, influenced by fossil fuel production, agriculture, and warming that releases stored methane from wetlands and permafrost.

“Methane is a significant factor causing us to hesitate in endorsing a hydrogen economy, as it inevitably leads to hydrogen leaks into the atmosphere,” emphasizes Archibald. “If hydrogen escapes into the atmosphere, it worsens the methane issue.”

It might spark discussion over the cautious use of hydrogen, especially if renewable energy cannot sufficiently replace fossil fuels, according to Archibald. Nonetheless, Patterson and other experts highlight that the warming effects from increased hydrogen use are expected to be minimal compared to the considerable warming impact of fossil fuels. “We don’t want to discourage people from pursuing hydrogen energy, as it’s a much cleaner option than its fossil fuel counterparts,” emphasizes Patterson.