Warming impacts of hydrogen emissions are overlooked, underestimated: EDF

The Environmental Defense Fund is sounding the alarm on the "overlooked and underestimated" warming impacts of hydrogen as emerging research shows that hydrogen's climate effects are akin to methane if allowed to leak into the atmosphere.

Until recently, science's understanding of how hydrogen interacts with the atmosphere has been limited. But new work in a growing body of research has found that hydrogen's potential warming effect is twice as high as previously thought, the EDF's study found, a potential stumbling block for nascent industry with huge decarbonization potential.

"I hate being that negative person," said Illissa Ocko, the lead author of the EDF's July 20 report, in an interview. "There's a lot of promise [for hydrogen], we're just trying to be careful here and push forward the best available science so that we can make the best decisions for ourselves and the climate."

Unlike well-studied greenhouse gasses like methane and CO2, hydrogen has a more indirect warming effect on the atmosphere. Once it escapes into the atmosphere, most hydrogen – around 70% to 80% – is absorbed by microbes and bacteria in soils. The reminder makes its way into the troposphere and stratosphere, where it encounters and reacts with hydroxyl radical (OH), a naturally occurring molecule that aggressively reacts with other molecules.

Methane, for instance – one of the most destructive greenhouse gasses – commonly reacts with OH, and that reaction is nature's way of breaking down and eliminating methane and other trace gasses from the atmosphere. But higher concentrations of hydrogen in the atmosphere reacting with OH leaves a smaller pool of OH to eat that methane.

As the study explains: "In the troposphere, less OH is available to react with methane; given that methane's reaction with OH is its primary sink, this leads to a longer atmospheric lifetime for methane, which accounts for around half of hydrogen's total indirect warming effect."

Hydrogen emissions also have two secondary warming effects. First, hydrogen molecules that have reacted with OH in the troposphere – the lowest region of the atmosphere – creates tropospheric ozone, or ground-level ozone, which is considered a greenhouse gas. Second, when hydrogen molecules react with OH in the stratosphere – the atmospheric band directly above the troposphere – they create more greenhouse gasses in the form of water vapor.

"A detailed understanding of climate effects is required to assess and compare competing decarbonization solutions like clean hydrogen and electrification," said Brian Murphy, hydrogen analyst at S&P Global Commodity Insights. "This EDF work moves hydrogen climate science forward, and should be integrated into project analysis as well as hydrogen emissions measurement, verification, and certification programs."

Measuring hydrogen's impacts

Like methane, a hydrogen molecule's lifespan in the atmosphere is considerably shorter than that of carbon, which is usually measured on a 100-year timescale. Hydrogen's warming impacts usually lasts between one and three years, the study found, while methane's impacts last for around a decade.

Measuring the impacts of shorter-term greenhouse gasses has proven challenging in a world that has come to adopt climate measurements based on CO2's 100-year timescale. After being standardized by the International Panel on Climate Change and the United Nations Framework Convention on Climate Change, it's become commonplace for climate agreements and environmental lifecycle assessments to base measurements on the 100-year scale.

This, Ocko said, has made it harder to understand the potency of emissions with shorter-term impacts, like hydrogen and methane.

"We saw this problem with methane, and we have been working on this issue for over a decade now in terms of trying to clarify methane's role in climate change because it's constantly being devalued by this metric that looks at the 100-year timescale," she said. "Hydrogen falls into this same category."

Industry reaction

It's not the first time the group's findings have been brought to light. In March, during the CERAWeek energy conference by S&P Global, EDF President Fred Krupp raised the specter of hydrogen's threat while on a panel.

"I've heard a lot about hydrogen, but so far nobody has mentioned that we could be creating a situation similar to what we did with methane, where the whole infrastructure was built without anyone paying attention to how much is leaking," Krupp said.

"The world hasn't recognized that we're rushing to build out this hydrogen infrastructure without realizing that ... some hydrogen, when it leaks, is 100 times more powerful, pound for pound, than CO2 is as a greenhouse gas," he said. "So for God's sake, before we build all this hydrogen infrastructure, let's design it in a way that it's only used for those uses that are appropriate."

But not all in the industry fully agree that the issue is as urgent as the EDF portrays it. During the March conference, SoCalGas' Senior Director of Business Development Yuri Freedman described Krupp's comments as overgeneralized and premature, adding that SoCalGas' own lab experiments show very small leakage rates of hydrogen.

"We are doing this engineering analysis bottom-up, and we can stand behind our conclusions because we have experimental data to prove them up," Freedman said. "I think that many of the conclusions and statements that are made are made without basis."

A SoCalGas spokesperson pointed to one study from the University of California-Irvine that has shown that hydrogen does not leak at higher rates than methane, despite being one of the world's smallest molecules. Those findings were confirmed by the company's own tests of a new technology that would allow hydrogen to be transported via natural gas pipeline.

Ocko has called SoCalGas' use of the UC-Irvine study a mischaracterization.

"Of course these natural gas companies want to preserve their infrastructure, so I totally see the business reason," she said. "But scientifically, for the environment and climate, it just makes no sense" to replace natural gas with hydrogen in many use cases instead of turning to electrification.