The shift came as electricity use started growing again after decades of little change. The rapid expansion of AI data centers is one factor, along with growing demand for air conditioning during hotter weather.

Utilities are now being asked to supply more power than they expected just a few years ago, said Steve Piper, director of North American power and renewables research at S&P Global Energy.

"You need more of everything," he said. "You need more green energy, of course, but you're also running your gas plants more, running your coal plants more, and that puts upward pressure on emissions."

Piper said coal also became more competitive with natural gas last year, citing the EIA report’s finding that fuel costs helped drive the jump in coal generation.

Across the West, utilities are racing to add new power plants and transmission lines. But those projects can take years to complete. That’s helping keep some coal plants online longer than expected, according to Rob Gramlich, president of Grid Strategies, an electric power consulting firm.

"Coal plants were, by and large, on their way to retiring, one by one, year by year,” Gramlich said. “But I think in many cases, they're being extended, and the pace of retirements is slowing."

Gramlich said renewable energy continues to grow, but utilities are also expected to rely more on natural gas in the near term, while they add the generation and transmission needed to meet growing electricity demand.

Both analysts said the long-term challenge is building enough new infrastructure to support a rapidly growing appetite for electricity while getting carbon emissions back on a downward path.