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Emissions of a gas that could be linked to global warming are one reason to be wary of a Duke Energy power plant proposal

North Carolina is in a population growth spurt, and that is likely to mean rising demand for energy to heat, cool and power all the new homes and businesses. Charlotte-based Duke Energy serves 2.2 million customers in the two Carolinas, including those in Durham and Orange counties, so the company by necessity is in the thick of confronting the energy supply problem.

Two new coal-fired power plants, which Duke seeks to build, are an important part of its response. It's understandable why the company would choose this course. The plants could be built on a relatively short time frame, coal is abundant, and other options have their own drawbacks. Still, Duke hasn't made a convincing case that those plants are needed or that they are the best solution.

Publicly regulated utilities are required by state law to justify big, expensive projects whose costs will be passed along to customers. In advance of a recent N.C. Utilities Commission hearing, Duke offered projections for demand intended to show the need for the two proposed 800-megawatt generators at its Cliffside facility near Shelby, west of Charlotte. The commission's Public Staff, which is responsible for looking after the interest of power customers, supports the company's request.

Environmental groups, however, cite Duke's disappointing record in the encouragement of power conservation and neglect of alternative energy sources -- wind and solar, for example. A principal objection to the plants is that they would emit large amounts of carbon dioxide, a so-called greenhouse gas suspected of being a factor in global warming. The N&O reported Saturday that the proposed Cliffside facility would emit the same amount of CO2 annually as a million automobiles -- 11.5 million tons.

State Attorney General Roy Cooper has added weight to the skepticism. In a filing with the commission, Cooper's office said the power demand that Duke cited to justify the two plants had dropped substantially, due in part to the loss of a pending wholesale contract. So while demand is up, Duke's own numbers appear to justify one plant, not two. The filing also agrees that Duke has not exploited energy alternatives to the point where the rate-paying public would benefit.

Duke's cost estimate for the Cliffside project has risen to $3 billion, 50 percent more than originally announced. The company's customers, including low-income ones, end up with the bill.

Customers would have to pay for power generated from alternative sources, too. But the cost of some alternatives has dropped in recent years as the technology has improved and as their use has expanded. (The company also is moving to win approval for new nuclear-powered units, which avoid air-pollution problems but pose other vexing issues with radioactive waste.)

Meanwhile, common sense argues that using less energy -- conserving it -- is cheaper than producing it. Duke executives acknowledged in the Utilities Commission proceedings that the company has no meaningful program to help homeowners and big commercial customers use energy more efficiently. Other states require utilities to have such programs, and to generate a certain amount of their power supply from alternative sources.

It's past time for North Carolina's legislature to do likewise. And unless Duke Energy has favorable data that it hasn't revealed, the Utilities Commission should protect electricity customers' checkbooks and insist on a higher level of environmental stewardship by denying the request for two new coal-fired plants.