Investments in coal power are becoming riskier as the price of greenhouse-gas emissions is factored into the cost of the fuel, according to a report by a consulting firm whose clients include the U.S. Energy Department.

Proposed coal-fired stations across the U.S. are being canceled or delayed as pending regulation of heat-trapping gases threatens returns on investments, Synapse Energy Economics Inc. said. The prospect of climate-change legislation in the U.S. has turned forecasting the operating costs for coal power plants into guesswork, according to Tuesday's report.

Investors want more information on how greenhouse-gas limits will affect coal plants while the U.S. Congress is investigating government loans for coal stations that lack emissions controls for greenhouse gases. Moody's Investors Service Monday said U.S. utility owners face the risk of downgrades to their credit ratings as they grapple with limits on carbon dioxide.

"From a financial investment and ratepayer point of view, you've got to consider the costs because it's a financial train wreck coming down the road," said David Schlissel, a senior consultant at Synapse, based in Cambridge, Mass., and lead author of its report.

More than 20 planned coal-fired plants were canceled in 2007 and 36 others were delayed, Synapse said. PacifiCorp, a utility unit of MidAmerican Energy, called off plans for a 700-megawatt coal station in Wyoming because the company couldn't fix the future costs of greenhouse-gas regulation, said PacifiCorp spokesman David Eskelsen.

MidAmerican Energy is 80 percent-owned by Warren Buffett's Berkshire Hathaway Inc. PacifiCorp has 10,000 megawatts of generating capacity in six states, 6,500 megawatts of which come from coal. The threat of regulation has pushed some utilities to turn to renewable power, energy efficiency and in some cases natural gas power plants.

PacifiCorp operates as Rocky Mountain Power in Utah, Idaho and Wyoming.

"Because of the political uncertainly regarding carbon regulation, construction of coal plants is not currently in the company's 10-year plan," Eskelsen said in an interview. "Until we have some certainty about what that regulation could be, we don't know."

Congress is debating legislation that would limit greenhouse-gas emissions from utilities, refineries and large manufacturers. One measure approved by a Senate committee in December would set a price on carbon through a market for emissions credits.

Climate-change legislation will probably have "significant effects on industry economics, operations and capital investment," Moody's Vice President Scott Solomon said Tuesday in a statement. "New rules would likely force the industry to spend billions of dollars on compliance."

The cost of global-warming gases are not properly accounted for in long-term risk forecasts by rating agencies such as Standard & Poor's, said Michael Dworkin, director of the Institute for Energy and the Environment at the Vermont School of Law. As a result, utilities should be investing heavily in renewable energy such as wind and solar power, Dworkin said Tuesday at a conference at the New York Society of Security Analysts.

"If you are $1 billion in your investment in a $2 billion facility and it turns out it's going to cost $3 billion, you don't quit," Dworkin said. "Coal plants are long-term, all-or-nothing investments. You have to think over decades."

The U.S. needs to spend at least $1.4 billion a year through 2030 on research and development to reduce greenhouse-gas emissions, the Electric Power Research Institute, an industry think-tank, said in a January article in its member magazine. Much of the research is needed to develop ways to capture and store carbon dioxide from coal-fueled plants, the largest single contributor to greenhouse gas emissions and source of half the nation's power, it said.

Equipment to capture carbon dioxide from power plants isn't commercially available, Larry Monroe, senior research consultant for Southern Co., the largest U.S. electricity producer, said Tuesday in a meeting with financial analysts.

The equipment might increase the cost of a typical plant by 75 percent, and as much as 30 percent of the power generated at a coal-burning station might be used up in capturing carbon dioxide and compressing it into a liquid for permanent storage, he said. The volume of carbon dioxide produced annually by U.S. coal plants is 2 billion metric tons, enough gas to fill Lake Michigan four times, Monroe said.

Southern's utilities supply 4.3 million homes and businesses in Georgia, Alabama, Florida and Mississippi. All four states allow the utilities to pass to customers the cost to comply with environmental regulators, Chief Executive Officer David Ratcliffe told analysts Tuesday.