With global warming a rising concern, some environmentalists are rethinking nuclear power because it emits zero greenhouse gases.

"You can't just write nuclear off," says Judi Greenwald, director of innovative solutions with the Pew Center on Global Climate Change, an environmental research and advocacy group. "I think everybody feels you have to at least look again" at nuclear power.

That attitude is markedly different from the revulsion that environmental groups have directed toward nukes for most of the past three decades.

That opposition is one of a number of factors that nuclear advocates say put in place a virtual ban on new nuclear plants since the late 1970s.

The times are changing. Earlier this month the Nuclear Regulatory Commission gave its preapproval for the site of a proposed new nuclear power plant in Illinois.

If built, the plant will be the first to be constructed since 1979, the year of the Three Mile Island accident near Harrisburg, Pa., that sparked a massive protest movement against nuclear plants.

"I have seen and felt a shift over the years," says Mary Quillian, director of business and environmental policy for the Nuclear Energy Institute.

Some foes won't budge

Some environmentalists aren't buying. "We remain steadfastly opposed to nuclear power," Sierra Club spokesman Josh Dorner said. "We're not willing to believe they are as safe as the industry is willing to portray them."

The Sierra Club says it has not wavered in its stand against nuclear power. Greenpeace USA also says it finds nuclear power unacceptable.

Both organizations cite the unresolved debate over long-term storage of radioactive wastes and economic viability because of huge construction costs. They also worry about the possibility of spent fuel getting into the wrong hands and being used for weapons.

"I think there are a lot better carbon-free alternatives for producing electricity," says Christopher Flavin, president of Worldwatch Institute, an environmental research group.

Among the concerns are accidents. Three Mile Island suffered a partial core meltdown that although the most serious accident for a nuclear plant in U.S. history it caused no deaths or injuries. Then there was the Chernobyl accident in the Soviet Union in 1986 on which several deaths were blamed directly.

Other environmentalists say the need to address global warming means taking a harder look at nuclear.

Besides Pew, at least three leading environmental organizations — Union of Concerned Scientists, Natural Resources Defense Council, and Environmental Defense — say they are willing to consider nuclear power as part of a long-term solution to global warming.

Bill Chameides, chief scientist for Environmental Defense, says his group's position "has evolved."

"Global warming is the environmental issue of our generation," he says. "Clearly to solve this problem we need to have all technologies on the table. Therefore, nuclear energy … needs to be considered."

However, he says a big expansion of nuclear power would be "foolhardy" until a solution is found for where to put nuclear wastes.

Christopher Paine, senior nuclear analyst with the Natural Resources Defense Council, says his group is also willing to give nuclear a look.

"Our position is that nuclear is not off the table as an energy source, but we believe there are cheaper, cleaner and faster ways to reduce pollution and provide reliable energy than nuclear power," Paine said.

Even the Union of Concerned Scientists, which has been sounding alarms about nuclear safety since before Three Mile Island, said in a position paper revised this month that nukes "should be considered as a longer-term option if other climate-neutral means for producing electricity prove inadequate."

Groups taking 'baby steps'

Nuclear already plays a big role in the USA. There are 104 nuclear reactors operating at 66 plants in the country, producing one-fifth of the nation's electricity, according to the Department of Energy. The highest user is Vermont, which gets 72.5% of its electricity from nuclear.

Coal provides far more electricity in the USA and creates greenhouse gases when burned.

Patrick Moore — a founder of Greenpeace who is now co-chairman of the industry-funded Clean and Safe Energy Coalition, which advocates for nuclear power — says coal-fired power plants pose a greater threat to the environment. He says environmental groups recognize that, even those not yet officially embracing nuclear power.

"The environmental groups know if they shut down coal, the utilities will have to go to nuclear," he says. "There's a real softening there."

"Baby steps" is how Quillian describes the shift among environmental groups. "Groups absolutely opposed to any nuclear have over the last few years started saying, 'well, we're just concerned about building new plants.' Now we're starting to see some groups soften even on that."