North Carolina, with its quickly growing population, posted the nation's fourth-biggest jump in carbon dioxide emissions from 1990 to 2004, says a study released Thursday by Environment North Carolina, an advocacy group.

Green energy backers such as state Reps. Pricey Harrison of Greensboro and Grier Martin of Raleigh, both Democrats, said the report underscores the urgency for North Carolina to develop policies that bolster the use of renewable energy, including wind, sun and water power, and to encourage energy conservation measures.

Such sources of natural energy reduce reliance on electricity generated by burning coal, which produces carbon dioxide and contributes to global warming.

A bill introduced by Harrison, Martin and others would ensure that renewable sources and conservation efforts would replace 20 percent of traditional energy production by 2021. A similar bill introduced by Sen. Charlie Albertson, a Duplin County Democrat, would have green efforts supply 10 percent of energy demand by 2018. Neither bill has been voted on yet.

North Carolina is among about 30 states that have no policy mandating environmentally friendly energy use.

Of the states that do have such requirements, none is in the Southeast. California, the nation's green energy leader, has passed laws requiring utilities to increase sales of renewable energy up to 20 percent by 2010.

But momentum is growing in North Carolina, Harrison said. She said backers of green energy legislation have support from House and Senate leaders to pass a renewable energy policy this year. That could make the state a leader in the region.

"I see a different atmosphere around here, embracing alternative energy," said Harrison, who unsuccessfully pushed a similar proposal last year. "This would be the state's first step toward significantly curbing global warming pollution."

The new carbon numbers released Thursday, based on state-by-state data of fossil fuel consumption from the federal government, indicate that greenhouse gases are a growing problem in North Carolina, as well as other states that have experienced population booms. Texas ranked first in growth of carbon dioxide emissions at 98 million metric tons, followed by Florida and Illinois, the report said.

North Carolina increased carbon dioxide emissions by an estimated 39.2 million metric tons -- a 36 percent increase. That was double the 18 percent increase in carbon dioxide emissions nationwide during the 15 year period.

Across the United States and in North Carolina, the higher emissions came primarily from growth -- more cars and trucks on the roads, and more electricity pumped into more homes and businesses. The state's population grew from 6.6 million to an estimated 8.5 million during that period, an increase of about 29 percent.

Both of the state's electric utilities have plans to expand production to meet increasing demands. Progress Energy and Duke Energy have expensive nuclear plants on the drawing boards. They would like lawmakers to add some form of assurance during construction that they'll eventually be able to recoup their costs through rate increases.

Dana Yeganian, a spokeswoman for Progress Energy, said a renewable energy policy may emerge as part of a broader energy bill that representatives of environmental groups, utilities and manufacturers have been negotiating.

Yeganian said that lawmakers must keep in mind that requiring a set amount of renewable energy could raise electricity costs, and residential, businesses and manufacturers should know what those costs are.

"What we have said is you have to keep in mind that there could be cost impacts," Yeganian said.

Carbon dioxide is a heat trapping gas that is produced naturally, but it's also the byproduct of human activities such as burning coal, oil and gas. The gases get caught in the atmosphere, creating a greenhouse effect that is warming the planet.

The average global temperature increased about 1 degree between 1900 and 2000, and the rate of warming has accelerated over the past 30 years.

A state panel on climate change is studying impacts of warmer temperatures in North Carolina and will make recommendations next year about steps the state could take to respond.