N.C. GreenPower, a Raleigh nonprofit that accepts public donations to subsidize green energy, is offering a half-price discount on its carbon offset program.

As a result, a donor can now reduce 1,000 pounds of someone else's greenhouse gas emissions with every $4 contribution. The donations go to efforts that reduce emissions of carbon dioxide or methane, typically tree-planting projects or technologies that flare off methane gas at landfills or hog lagoons.

The N.C. Utilities Commission, which regulates the carbon offsets program in this state, approved N.C. GreenPower's new price plan Tuesday. The new prices are effective retroactively to Aug. 1.

For the past three years, N.C. GreenPower had been offering to offset 500 pounds of greenhouse gases for $4, but the organization is doubling the value because the market price for carbon offsets is dropping.

Such offset programs are popular among people who are concerned about global warming and are willing to pay others to reduce their greenhouse gas emissions. Skeptics dismiss such programs as guilt fees that pay for programs that would have been implemented anyway.

N.C. GreenPower's is one of dozens of carbon offset programs around the country, but it is one of the few that is regulated by a government agency.