The renewed push for legislation to cut greenhouse gas emissions could falter over an old debate: whether nuclear power should play a role in any federal attack on climate change.
Congress, with added impetus from a Supreme Court ruling last week, appears more likely to pass comprehensive energy legislation. But nuclear power sharply divides lawmakers who agree on mandatory caps on carbon dioxide emissions. And it has pitted some on Capitol Hill against their usual allies, environmentalists, who largely oppose any expansion of nuclear power.
House Speaker Nancy Pelosi and Sen. Barbara Boxer -- Bay Area Democrats with similar political views -- are on opposite sides.
Pelosi used to be an ardent foe of nuclear power but now holds a different view. "I think it has to be on the table," she said.
Boxer, head of the Senate committee that will take the lead in writing global warming legislation, said that turning from fossil fuels to nuclear power was "trading one problem for another."
Sens. John McCain (R-Ariz.), Barack Obama (D-Ill.) and Hillary Rodham Clinton (D-N.Y.) -- all presidential candidates -- support legislation that would cap greenhouse gas emissions and provide incentives to power companies to build more nuclear plants.
Opponents of nuclear power say that because a terrorist attack on a plant could be catastrophic, it makes no sense to build more potential targets. And radioactive waste still has no permanent burial site, they say, despite officials' three decades of trying to find one.
But attitudes toward nuclear power may be shifting as a consensus emerges that greenhouse gases are causing the world to heat up.
The Supreme Court added its voice, criticizing the Bush administration for not acting to control greenhouse gases.
Max Schulz, a former Energy Department staff member who is a senior fellow at the Manhattan Institute, a conservative think tank, said the ruling could help "spur the revival of nuclear power."
And congressional Democratic leaders have made passage of global warming legislation a priority.
"I've never been a fan of nuclear energy," said Sen. Dianne Feinstein (D-Calif.), who has called it expensive and risky. "But reducing emissions from the electricity sector presents a major challenge. And if we can be assured that new technologies help to produce nuclear energy safely and cleanly, then I think we have to take a look at it."
The public's attitude toward nuclear power is more favorable when such energy is seen as part of an effort to fight climate change. Polls over the years have shown that a slim majority backs nuclear power, but a Los Angeles Times/Bloomberg survey last summer found that a larger majority, 61%, supported the increased use of nuclear energy "to prevent global warming."
Legislation introduced recently in California seeks to repeal a 1976 ban on new nuclear plants in the state.
"There's no question that the attention to climate change over the last several years has materially changed the public discussion of nuclear power," said Jason Grumet, executive director of the National Commission on Energy Policy, a bipartisan group of energy experts. Given the threat of global warming, he said, "it's hard to ignore the principal source of noncarbon power generation in the country today."
One environmental group has tried to keep an open mind. "We don't think any options should be taken off the table when dealing with global warming," said Environmental Defense spokesman Charlie Miller.
The nuclear power industry in the U.S. has been at a virtual standstill because of high construction costs, regulatory uncertainties and public apprehension after a 1979 accident at Pennsylvania's Three Mile Island.
A number of plants ordered before the accident went into operation. But many more were canceled after one of the Three Mile Island reactors suffered a partial meltdown and small amounts of radiation were released into the atmosphere.
Reviving the industry has been a priority for President Bush, who sees nuclear power as crucial to meeting a growing demand for electricity.
The Nuclear Regulatory Commission expects to receive applications for about two dozen new plants in the next few years -- in part because of provisions in a 2005 energy bill designed to promote nuclear power.
Currently, 103 nuclear plants -- including Diablo Canyon near San Luis Obispo and San Onofre in northern San Diego County -- generate about 20% of the nation's electricity.
The amount of congressional support for nuclear power is unclear.
When McCain and Sen. Joe Lieberman (I-Conn.) added subsidies for nuclear power to their 2005 bill to cut greenhouse gas emissions, they lost support from environmentalists and votes in Congress, including Boxer's.
McCain said he had no idea whether he would be more successful this time. But he said there was "no way that you could ever seriously attack the issue of greenhouse gas emissions without nuclear power, and anybody who tells you differently is not telling the truth."
On Capitol Hill last month, former Vice President Al Gore, who has become a leading advocate for swift action on climate change, said he saw nuclear plants as a "small part" of the strategy.
"They're so expensive, and they take so long to build, and at present they only come in one size: extra large," he said.
"And people don't want to make that kind of investment in an uncertain market for energy demand."
The McCain-Lieberman bill, which seeks to reduce greenhouse gas emissions by 2050 to a third of 2000 levels, would provide federal loans or guarantees to subsidize as many as three advanced reactor projects.
The U.S. Public Interest Research Group and Public Citizen said the bill would authorize more than $3.7 billion in subsidies for new nuclear plants.
Sen. Thomas R. Carper (D-Del.), a cosponsor of the McCain-Lieberman legislation, thinks support for nuclear power could bring more votes.
"Three or four years ago, if you included nuclear, you lost more than you gained," he said. "Today ... you pick up more than you lose."
But nuclear power faces huge political and economic obstacles.
Senate Majority Leader Harry Reid (D-Nev.) remains opposed to the planned Yucca Mountain nuclear waste disposal site in his state.
And Philip E. Clapp, president of the National Environmental Trust, said he did not think subsidies could overcome the concerns of potential investors. "There isn't enough money in the federal till to change Wall Street's calculation of the financial risks," he said.
Even some lawmakers who support nuclear power question whether the industry needs more federal money.
Sen. Jeff Bingaman (D-N.M.), chairman of the Senate Energy and Natural Resources Committee, sees nuclear power as a "mature industry," said Bill Wicker, his spokesman. "Emerging climate-friendly and genuinely renewable technologies like wind and solar and geothermal and biomass could use that [funding] boost," Wicker said.
Some environmentalists remain steadfastly opposed to nuclear power.
"Investments in energy conservation and renewable energy are quicker, more cost-effective and sustainable ways to reduce global warming emissions," said Erich Pica of Friends of the Earth, which will oppose McCain's bill as long as it contains subsidies for nuclear power.
Such environmentalists also note that carbon emissions from nuclear fuel processing are significant. They say the costs and risks of nuclear power are too high and far greater than alternatives, such as solar and wind power.
"Switching from coal to nukes," said Dan Becker, director of the Sierra Club's global warming program, "is like giving up smoking and taking up crack."