America’s transition to a clean energy economy is irrevocably underway and delivering deep pollution reductions, with coal use at record lows but renewable energy higher than ever, according to the Fourth Annual Energy Report released today by the Natural Resources Defense Council (NRDC). One sign of how far things have advanced: more than one-fifth of the U.S. population lives in a state with a goal of at least 50 percent renewable energy.

“The United States is changing fundamentally across the energy sector, accelerating away from fossil fuels into a clean energy future,” the new NRDC report notes. “The trend, obvious for more than a decade, is a combined product of state and federal policy harmonized with potent economic forces. Coal-fired generation dropped to historic lows this year, producing only one-third of our electricity, while renewable energy generation reached record highs, with more than one-eighth of America’s electricity generated from solar panels, wind turbines, and other renewable resources.”

As the NRDC report shows, smarter energy use in homes, buildings, and appliances reduces the need for dirty fuels and allows utilities to avoid building polluting power plants, lowering customer bills and emissions levels. The United States has also worked to reduce pollution from the transportation sector by improving vehicle efficiency through standards, advancing cleaner fuels, promoting electric vehicle use, and improving land use practices.

According to the report, oil consumption in 2015 was 12 percent below its 2005 peak. Primarily as a result of historically low coal use, energy efficiency gains, and soaring generation from solar and wind, 2015 marked a milestone in modern U.S. history: carbon dioxide emissions from electric generation dropped below those of the entire transportation sector for half of the year.

“The nationwide momentum for pollution-free energy is undeniable and irresistible because clean energy now costs less than dirty energy,” said Ralph Cavanagh, co-director of the NRDC Energy Program and a report co-author. “However, strong local, state, and federal policies are necessary for the United States to remain competitive globally and ensure clean energy technology and employment surge to the highest possible levels here at home.”

“The past year in energy saw a number of victories for the environment, highlighted by a global climate agreement and a carbon pollution reduction plan for the United States,” added Kala Viswanthan, a report co-author. “A clean energy revolution is underway, decarbonizing the electric grid through carbon reduction targets, energy efficiency gains, and renewable energy additions.”

The NRDC report, Accelerating into a Clean Energy Future, notes that the “United States helped achieve a successful agreement at the historic global climate negotiations in Paris at the Conference of the Parties 21 (COP 21). As energy policy expert Michael Grunwald wrote shortly after the 2016 presidential election, ‘even if [the United States were] to withdraw from the Paris climate deal, the U.S. is on track to fulfill its pledges under that deal.’”

To continue the clean energy progress, the NRDC report urges the federal government to remain an active partner in a clean energy transition. States should strengthen renewable portfolio standards that require a specific amount of energy generation from emissions-free sources like wind and solar. Utilities and their regulators should curb power plant emissions and prioritize renewable energy and energy efficiency. The transportation sector should incentivize electric vehicles and strengthen fuel economy standards to continue reducing U.S. reliance on oil. Clean energy companies and businesses should also lead the way, creating jobs for the sustainable energy economy.