McAuliffe, in the wake of President Donald Trump’s rejection of the Clean Power Plan — former President Barack Obama’s signature rule to limit emissions from power plants — directed the DEQ to develop a regulation that allows for the use of “market-based mechanisms and the trading of carbon dioxide allowances through a multi-state trading program.”

There is only one such program: The Regional Greenhouse Gas Initiative, a cooperative effort between nine Northeast and Mid-Atlantic states, sets regional yearly caps for carbon emissions, regulates emissions from fossil fuel power plants above 25 megawatts, and auctions off those carbon-dioxide “allowances.” The proceeds are invested in programs that improve energy efficiency and advance renewable energy technology.

“We are going to be talking quite a bit about how we could plug into RGGI,” said DEQ Director David Paylor. “There are some different ways to do that.”

Covered plants have to measure and monitor emissions and must have allowances equal to or exceeding their carbon output. Virginia’s power plants put out nearly 34 million tons of carbon dioxide in 2016, up from 31 million in 2011, according to a DEQ presentation. Emissions were projected to increase to 37 million tons in 2019 and then fall to about 34.8 million tons by 2023.