Opinion | Hydrogen Power Isn’t as Green as It Looks

Hydrogen production today is dirty and energy-intensive. Methods exist that could virtually eliminate the greenhouse-gas emissions, but there’s a more fundamental challenge: Hydrogen itself contributes to climate change when it leaks into the atmosphere.

Scientists have long known that hydrogen triggers indirect warming effects in the atmosphere. As the smallest possible molecule, it is difficult to contain. More, the latest research reveals that—depending on time frame—hydrogen’s warming power is two to six times as great as previously recognized.

New peer-reviewed research by scientists at the Environmental Defense Fund shows that the climate impact even of ostensibly clean hydrogen rests on how much escapes into the atmosphere. At a low leak rate, the EDF estimates, both “green” hydrogen made using zero-emission electricity and water, and to a lesser extent, “blue” hydrogen made from natural gas (with residual carbon dioxide captured and minimal upstream methane emissions), would dramatically reduce warming impact compared with fossil fuels.

But if leakage of both hydrogen and methane is high, then hydrogen from natural gas could actually increase the 20-year warming impact. Green hydrogen would still be better for the climate over 20 years than the fossil equivalent, but far less so than the climate-neutral promise boosters claim.

Unfortunately, there are currently no data to suggest how much hydrogen might leak in the real world. Existing monitors detect only concentrations high enough to risk explosion (a new generation of devices that can do the job is on the horizon). We do know that leakage will depend on how hydrogen is produced, transported and used.

Hydrogen is most appropriate in activities such as steel and cement production, for which there are no better alternatives, or as feedstock for advanced low-carbon fuels for ships and planes. But it makes no sense to divert renewable energy to make hydrogen for use in cars or homes, where electricity can be used directly instead. And since transporting hydrogen likely increases leakage risk, it’s better to produce it close to where it’s used.

Equally important, hydrogen is no solution at all if it harms local communities. Water consumption and air pollution from production and use of hydrogen must factor into deployment decisions; people living nearby must be engaged from the start.

For “clean” hydrogen to deliver on its promise, these challenges must be addressed now. It’s cheaper and easier to build it right the first time than to fix it later.

Mr. Krupp is president of the Environmental Defense Fund.