GILLETTE -- California moved Thursday to ban electricity from major greenhouse gas sources, an action that came as no surprise for Wyoming energy officials hoping to ship more Cowboy State coal by wire.

The California Public Utilities Commission voted 4-0 to adopt the "greenhouse gas emissions performance standard," which will prohibit utilities and other energy providers from entering long-term contracts with sources that emit more carbon dioxide than a modern natural gas plant.

"It represents a significant milestone in our ongoing efforts to address the challenge of climate change," California PUC President Michael Peevey said.

The new rules are expected to affect energy markets across the West. While there are almost no coal-fired plants in California, about 20 percent of the state's electricity comes from coal plants in Nevada, Wyoming, Utah and other Western states.

The new standard is aimed at encouraging investment in cleaner energy sources such as wind and solar, while discouraging use of coal and other high-polluting sources. Coal is cheap and plentiful, but releases high levels of carbon dioxide, a gas blamed for trapping heat in the earth's atmosphere and raising temperatures worldwide.

California's initiative does expressly exempt electricity derived from coal-gasification processes that have a carbon dioxide sequestration component, and will keep alive ideas such as the high-capacity Wyoming-to-California Frontier Line.

"We continue to go down the path of exploring a high-capacity transmission line bundled with some high-quality Wyoming wind, if California customers are willing to pay for it," said Steve Waddington, executive director of the Wyoming Infrastructure Authority.