The U.S. Energy Information Administration (EIA) projects that 2016 is the tipping year from coal to natural gas in the fueling of U.S. power generation facilities.

The EIA’s Short Term Energy Outlook forecasts that gas will provide 33% of electricity this year while coal’s share dips to 32%—the first time that gas will have the largest share for a year. The share of non-hydro renewables is expected to rise to 8%. Hydropower’s share is forecast to be 6%.

Though coal has long been the dominant energy source for producing electricity in the U.S., natural gas first surpassed coal on a monthly basis in April 2015 and the two fuels provided virtually the same amount of electricity generation last year.

Despite the advantages of natural gas over coal from an environmental perspective, economics has driven this trend. The huge increase in gas output from shale fields that began in 2009 narrowed the price difference between coal and gas and slowly cut into coal’s 50% market share. The mild winter of 2011-2012 contributed to lower natural gas prices and a displacement of some coal-fired generation. Coal recaptured some of that share when gas prices rose during 2013 and 2014 but lost its advantage when oil and gas prices plummeted.

“Cheaper and more plentiful natural gas has fundamentally shifted our entire generation fleet,” Tom Williams, spokesman for Duke Energy, told Hart Energy in a story to be published in the April issue of Midstream Business. “We’ve shut down 40 coal units since 2011 and almost all of that capacity has been replaced by natural gas plants.”

The EIA believes that environmental regulations have played a secondary role in the decline of coal’s generation share, but some owners of coal-fired plants may be forced to choose between retiring or reducing the utilization rate to comply with the Clean Power Plan, which requires lower CO2 emissions from existing fossil fuel-fired power plants.

The plan is scheduled to take effect in 2022 but has been stayed by the Supreme Court while awaiting the outcome of ongoing litigation.

“There’s a lot of uncertainty regarding the implementation of the Clean Power Plan,” John Kneiss, Washington-based director for Stratas Advisors, told Midstream Business in the article, “in particular, the time line that may take place because of the litigation.”

While a nominee, Merrick Garland, has been chosen by President Obama to succeed the late Associate Justice Antonin Scalia on the Supreme Court, it is not certain that the vacant seat will be filled this year. Kneiss said the Clean Air Act is unlikely to be considered until the court is full.

“This case is big enough and significant enough that it will wait until there are nine justices,” he said. “There was a good chance the Supreme Court would have found faults with it and remanded it back to the EPA to make some changes based on the way the agency took its authority to regulate under the Clean Air Act.”

Coal’s share of the power generation market has also been chipped away by the growth of renewable energy sources, especially wind and solar, the EIA said. Unlike the increased use of gas, which was market-driven, the growth of renewables was pushed by a combination of state and federal policies.

Joseph Markman can be reached at jmarkman@hartenergy.com and @JHMarkman.