JUDY WOODRUFF: So, how meaningful are this weekend's pledges? And does it signal a fundamental change in how we will get our energy?

Fred Krupp is the president of the Environmental Defense Fund. He's back from Paris. And Robert Bryce is a senior fellow at the Manhattan Institute and the author of several books about this. His latest is titled "Smaller, Faster, Lighter, Denser, Cheaper."

And we welcome you both to the program.

Fred Krupp, to you first. How much of a difference is this agreement going to make?

FRED KRUPP, Environmental Defense Fund: It's going to make a big difference. It's really the first COP that exceeded the expectations that I had going into it, the first conference of the parties that really set us on a path toward solving this problem.

Now, Judy, it doesn't solve the climate problem. No one meeting could do that, not by a long shot, but it does get us a long way there. The reductions that have been pledged by nearly every country on Earth get us perhaps halfway there. And then there is a mechanism built into the agreement that allows the ambitions to be ratcheted up.

And, perhaps most important, there is transparency, which means countries will have to be reporting their emissions, and there will be a technical review of those reports to make sure they're accurate. And that is critical, so that there is not only ambition here, but also accountability.

JUDY WOODRUFF: Robert Bryce, do you see this as an agreement that goes a long way toward doing something about climate change?

ROBERT BRYCE, Manhattan Institute: I do not.

I think there are three key problems with it, Judy. First is, none of these targets that have been set by the individual countries are legally binding. Second, Ban Ki-Moon, the U.N. secretary-general, made this clear before the meeting started in Paris when he said that all of these targets that have been made by the individual countries are not sufficient, and that they're going to have to come back in just a few years and provide new lower targets for emissions.

And, finally, and perhaps most importantly, there is nothing in any of these agreements that moves the ball forward on nuclear energy, and this is the key issue. When you listen to what the climate scientists have been saying on this, on December 3, in The Guardian, James Hansen, one of the most high-profile climate scientists in the world, along with three other climate scientists, said that nuclear energy will make the difference — I'm quoting — "make the difference between the world missing crucial climate targets or achieving them."

And the hard reality is that, unless we have an energy form that can replace substantial quantities of coal-fired generation — and that means natural gas and nuclear — then I think that we're not going to come near any kind of significant reductions in CO2 emissions to meet the CO2 emissions targets that have been laid out.

JUDY WOODRUFF: Well, Fred Krupp, let me take his — Mr. Bryce's last point first, that the agreement doesn't make meaningful progress on moving toward nuclear or another real alternative to carbon.

FRED KRUPP: Well, I would strongly disagree with that.

Countries are free to meet their obligations any way they want to, but they have to report and be accountable, as I said before. China plans to build 30 nuclear power plants and is constructing about half that number now. So, if nuclear technology comes along that's safe and affordable, nuclear very much is on the table and could be part of the agreement.

JUDY WOODRUFF: But, Fred Krupp, there is no requirement that countries do that. Is that correct?

FRED KRUPP: Well, there is no requirement that countries use nuclear, no. They're free to use whatever technology they choose.

But some countries are pursuing nuclear, and that's allowed. It turns out, Judy, that the cost of solar panels in the last five years has dropped 80 percent. So, if solar panels are cheaper than nuclear, why should the — an agreement require countries to use nuclear? Nuclear may end up cheaper. That remains to be seen. Right now, the plants that are being built in the United States will substantially raise the rates of rate payers in the jurisdictions where those are being built, because, right now, it is an expensive technology, at least here in the U.S.

JUDY WOODRUFF: Robert Bryce, why isn't it sufficient, if not — even the advocates of this agreement are saying it's not perfect, but why isn't it sufficient that countries are now saying they're going to move in the direction, not all necessarily nuclear, but these other technologies, alternative fuel technologies?

ROBERT BRYCE: Sure. And we hear about solar and wind. And we have heard about solar and wind.

And, look, I'm pro-solar. I have solar panels on the roof of my house. I'm not bullish on wind, because it takes up too much land. The problem, fundamentally, for the developing world is that they're not turning to solar and wind in a big way. They're turning to coal-fired capacity.

Let's look at the numbers that have been published by Sierra Club and CoalSwarm, two adamant coal critics. They point out that, today, there is 276 gigawatts of coal-fired capacity under construction now. That's roughly equal to the entire coal-fired capacity of the United States.

Mr. Krupp says we have to make nuclear safer and cheaper. There's no question. But to make that happen, we have to have strong governmental leadership. I have written many times about this. I had a piece in The L.A. Times just a few days ago. The United States could be taking a leadership position in making nuclear energy safer, cheaper, developing reactors that are passively safe.

But we don't have the support — this is key — of the main environmental groups, including the Environmental Defense Fund. Sierra Club and Green Peace are adamantly opposed to nuclear energy.

JUDY WOODRUFF: All right. Excuse me.

ROBERT BRYCE: Sure.

JUDY WOODRUFF: I'm sorry for interrupting, but let me let Mr. Krupp respond.

FRED KRUPP: First of all, we're not opposed to nuclear energy.

Second of all, the statistics about 276 plants, those were statistics from a few years ago. And that was planned, not under construction. But we had a lot of plants planned in the United States just a few short years ago, and they have almost all, to a one, been scrapped.

So, India's plans to build coal-fired plants — change will come to India, because it's in their own national interest. Sure, they have to lift people out of poverty. They need electricity. They need economic development, but they also need clean air. Right now, they have more opportunities than ever before to create jobs with renewable energy and to have clean air. The air pollution is killing hundreds of thousands of people a year in India.

So all I would say, Mr. Bryce, to you is that no one predicted how fast natural gas came online in the United States. It was a big change. And the change we're seeing now that I think will surprise a lot of people is how fast the cost of these clean energy technologies are coming down.

JUDY WOODRUFF: All right, gentlemen, big subject. We are clearly going to be coming back to it a lot in the future.

I want to thank both of you, Fred Krupp, Robert Bryce. Thank you.

ROBERT BRYCE: Thank you.

FRED KRUPP: Thank you.