Carbon dioxide levels in the atmosphere are already too high and plans to burn remaining coal and oil reserves should be scrapped, said James Hansen, director of NASA's Goddard Institute for Space Studies.

Coal-burning power plants increase concentrations of carbon dioxide, which contributes to global warming by trapping heat close to the earth. Companies such as Duke Energy Corp., planning to build new coal plants, don't "appreciate the gravity of the situation," Hansen's report says.

Hansen, who in 1981 warned that global warming emissions were heating the planet faster than expected, will submit his latest research this week to the journal Science, he said in an e-mail. "Catastrophic climate change" can still be avoided through conservation and greater use of renewable energy.

"It has become clear that continued emissions carry great danger," Hansen wrote in a March 25 letter to James Rogers, chief executive officer of Duke, based in Charlotte, N.C. "If you insist that new coal plants are essential for near-term power needs, you may submit your company and your customers to grave financial risk, and leave a legacy that you will regret."

Scientists continue to debate how much carbon can be pumped into the atmosphere before the worst effects of climate change, including droughts, floods and reduced fresh water supplies, become irreversible. Concentrations of carbon in the atmosphere are about 385 parts per million.

The European Union says that global warming needs to be kept to 2 degrees Celsius (3.6 Fahrenheit) to avoid the worst effects of climate change. A scenario to stay below that limit suggests that carbon levels must be stabilized between 350 and to 400 ppm.

"What this paper makes clear is that we have already passed the level of atmospheric CO2 that we can afford to leave in the air in the long run," Hansen said in an e-mail. Carbon can be reduced below "the dangerous level this century, but only if, over the next few decades, we phase out coal plants that do not sequester their carbon dioxide."

Carbon sequestration involves capturing the gas and injecting it for storage underground. The technology is being developed at a handful of pilot programs, and has yet to be demonstrated at commercial scale.

In his letter, Hansen applauded Rogers for public statements that "recognize the climate problem," and noted that Rogers attended a talk on climate change in November in Charlotte. Hansen provided his latest research, "Target Atmospheric CO2: Where Should Humanity Aim?" with the letter.

Duke is the third-biggest U.S. coal burner behind Southern Co., based in Atlanta, and American Electric Power Co. of Columbus, Ohio. The company is building a $2.4 billion, 800- megawatt coal plant 50 miles west of Charlotte, and a $2 billion, 630-megawatt plant in Indiana.

One megawatt is enough to power 800 typical U.S. homes.

In North Carolina, Duke agreed to close 1,000 megawatts of older coal plants. In Indiana, the company agreed to study the feasibility of capturing carbon from its new power plant.

Emissions in North Carolina are "being kept flat," Tom Williams, a spokesman for Duke, said in an interview. The Indiana plant "is being used to take the technology to an entirely new level. We hope that site will be the first large-scale sequestration initiative."

Building new coal plants in North Carolina and Indiana without technology to capture and store carbon would be a "foreseeable waste of money" and "a tragic mistake for Duke," Hansen said in the letter. Hansen offered to arrange a one-day discussion with experts in renewable energy, energy efficiency and carbon capture to help Rogers consider alternatives.

"We must begin to move now toward the era beyond fossil fuels," according to the report. "Continued growth of greenhouse gas emissions, for just another decade, practically eliminates the possibility of near-term return of atmospheric composition beneath the tipping level for catastrophic effects."