The amount of carbon dioxide, the leading greenhouse gas, released by US power plants grew by nearly 3 percent last year, the largest annual increase in nearly a decade, an environmental group said. The analysis of government emissions figures covered more than 1,000 plants including those burning coal, natural gas and oil. The report issued Tuesday by the Environmental Integrity Project, a Washington-based advocacy group, said that the 2.9 percent increase in CO2 releases outpaced a 2.3 percent year-to-year increase in electricity production. "Carbon emissions actually increased faster than (electricity) demand," said Eric Schaeffer, the group's executive director. He said reduced efficiency of older coal-burning power plants that often are some of the largest coal burners may have been one reason for the CO2 increase. The report said that Texas, Georgia, Arizona, California and Pennsylvania had the biggest one-year increases.