America’s coal-burning power plants are shutting down at a rapid pace, forcing electric utilities to face the next big climate question: Embrace natural gas, or shift aggressively to renewable energy?

Some large utilities, including Xcel Energy in the Upper Midwest, are now planning to sharply cut their coal and gas use in favor of clean and abundant wind and solar power, which have steadily fallen in cost. But in the Southeast and other regions, natural gas continues to dominate, because of its reliability and low prices driven by the fracking boom. Nationwide, energy companies plan to add at least 150 new gas plants and thousands of miles of pipelines in the years ahead.

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A rush to build gas-fired plants, even though they emit only half as much carbon pollution as coal, has the potential to lock in decades of new fossil-fuel use right as scientists say emissions need to fall drastically by midcentury to avert the worst impacts of global warming.

“Gas infrastructure that’s built today is going to be with us for 30 years,” said Daniel Cohan, an associate professor of civil and environmental engineering at Rice University.