"Of course, it's possible to erect tens of thousands of windmills but only at an extreme cost and waste of natural space," he said. "And still it would not be able to deliver electricity when it is needed."
There are 65 commercially operating nuclear plants in the U.S., including 104 reactors. Five new reactors are currently being built, in Georgia, South Carolina and Tennessee. In the past year, utilities have permanently shut down four others and plan to take a fifth out of service in 2014. At least two other planned projects have been shelved.
"Nuclear power is dying a slow death in the market place, which is what matters in determining its future," said Cavanagh.
As an alternative, the NRDC is touting efficiency. Energy-saving technology is becoming so successful, according to a new NRDC report, that efficiency has "significant potential to dramatically reduce power plant emissions." Total U.S. energy use peaked in 2007 and has been trending downward ever since, the NRDC says.
On the other hand, scientists in "Pandora's Promise" claim energy consumption globally could double by 2050 -- and perhaps triple or quadruple by 2100 -- as growing nations like China, India and Brazil start to want more energy.
A United Nations report released last month re-confirmed Hansen's fears. The study concluded that the planet is heating up, the oceans are rising and there's more evidence that neither development is natural.
Hansen, who was among the initial wave of scientists warning about climate change in the 1980s, said Friday he fears most its "irreversible effects."
"Once we get to a certain point and the ice sheets start to disintegrate, then you can't stop it."
Then Hansen paused. "And we're getting very close to that point."
If we stay on the current path, he said, "those are the consequences we'll be leaving to our children. The best candidate to avoid that is nuclear power. It's ready now. We need to take advantage of it."