Three million miles of natural gas pipelines criss-cross the U.S., and the fight against climate change could render them all obsolete. The last two weeks alone illustrate the stakes. President Joe Biden canceled the permit for the $9 billion Keystone XL oil pipeline on his first day in office, a clear signal any new fossil fuel pipeline project in the U.S. will face long odds. His climate envoy, former Secretary of State John Kerry, warned that natural gas pipelines could become “stranded assets” within 30 years as the administration seeks to end carbon emissions from power plants. And NextEra Energy Inc. wrote off $1.2 billion of its investment in the Mountain Valley gas pipeline from West Virginia to Virginia, which has been tied up in regulatory and legal delays.

So pipeline owners are eyeing another, possibly future-proof fuel: hydrogen.

It could, in other words, be a savior for the businesses behind our fossil fuel infrastructure. Even as those same companies insist gas will play a role for years to come, many of them are talking up the potential of hydrogen. They’re launching projects to blend small portions of hydrogen into their existing networks to see how the equipment behaves. They’re running experiments to strip hydrogen out of that blended gas, for use at specific locations. And they’re exploring how they might eventually transition from one fuel to the other.

“We see our gas network as an energy system that delivers molecules to our customers, and by 2050, the source of those molecules will be very different,” said Sheri Givens, vice president of U.S. regulatory and customer strategy at National Grid. “We see hydrogen as the low-carbon molecule of the 21st century.”

But the hype is far from the reality.

Some climate activists battling the industry over gas bans call the companies’ talk of hydrogen greenwashing. Gas businesses are downplaying the difficulty of switching from one fuel to the other, they say, trying to convince investors they’ll still be relevant in a zero-carbon world. “The industry’s always putting out things that might happen—if we just keep using gas right now,” said Matt Vespa, staff attorney with Earthjustice.

So far, there’s more actual hydrogen activity in Europe and the U.K. than there is in the U.S., where some companies have expressed interest without revealing many specific plans. The then-chief commercial officer of Energy Transfer, the largest U.S. pipeline operator by revenue, last fall called hydrogen “a head-scratcher” that, at least for now, doesn’t make sense. “At this point, we don’t see anything close on the horizon around hydrogen,” said Marshall S. McCrea, now the company’s co-chief executive officer.

The questions involved in hydrogen transport go beyond merely the will to pursue it. Gas pipeline owners can’t simply switch from one gas to the other without cutting off existing customers, so any transition would start with blending hydrogen into the existing stream of fuel.