CASPER, WYO. — New rules to cut carbon dioxide emissions nationwide could force utilities to have to shut down four coal-fired power plants in Wyoming years before they would be obsolete otherwise, said the chairman of the Wyoming Public Service Commission.

The proposed rules overestimate utilities’ ability to improve the efficiency of coal-fired power plants and overstate the potential growth of renewable power, Wyoming Public Service Commission Chairman Alan Minier told U.S. Environmental Protection Agency Administrator Gina McCarthy in a Nov. 21 letter.

The requirement for Wyoming to cut carbon emissions 19 percent would force closure of the Naughton, Dave Johnston, Jim Bridger and Wyodak power plants by 2030, Minier wrote.

“I’m trying not to sound alarmist, but it seems to me the scale at which this would affect us, because we are exporters of electricity and coal, I think it will impact our economy in a materially adverse way,” Minier told the Casper Star-Tribune (http://bit.ly/1zFS7jc ). “The biggest problem is the target because it is too aggressive for us.”

The EPA seeks a 30-percent cut in carbon emissions nationwide from 2005 levels by 2030. EPA officials have argued that efficiency improvements in the rules would offset higher energy costs. The plan attempts to curb carbon emissions through improved efficiency of coal-fired power, increased natural gas-fired and renewable power, and better energy conservation.

Almost 90 percent of the electricity generated in Wyoming, the top coal-producing state, comes from burning coal. Wyoming exports considerably more electricity than it uses in state.

Yet Wyoming would not receive credit for large renewable energy projects such as the planned 2,000- to 3,000-megawatt Chokecherry-Sierra Madre wind farm in Carbon County, Minier said. Credit for such projects would go toward the carbon targets of the states using that electricity, he said.

Richard Garrett, an energy analyst with the Wyoming Outdoor Council, said Minier’s comments don’t address what to do about climate change, which is the whole reason for the plan.

Wyoming could implement a renewable-power standard that would require a certain percentage of electricity to come from low-carbon sources, Garrett said. Meanwhile, the plan could boost demand for cleaner-burning natural gas. Wyoming is among the top gas-producing states, he said.

“Wyoming derives significant revenues from the sale of that gas,” Garrett said. “That looks like a win-win for the state and the environment.”