The lofty speeches have already begun, but what do leaders gathering in Paris this week hope to accomplish? And what could get in the way?

　　We check in with Seth Borenstein, a science writer for the Associated Press. He joins us tonight from Paris. And Michael Levi is with the Council on Foreign Relations. He's the director of its Program on Energy, Security and Climate Change.

　　Gentlemen, welcome to you both.

　　Seth Borenstein, what are all these nations gathered in one place hoping to accomplish this time?

　　今年的巴黎气候大会与往年有何不同?

　　SETH BORENSTEIN, Associated Press: Well, this time, they're hoping to come up with some kind of deal, a binding deal that could reduce the amount of carbon emissions coming from fossil-burning fossil fuels. They have tried year after year, and have failed year after year in the past.

　　GWEN IFILL: When you say binding, I just want you to clarify that. Do you mean binding on nations to hit certain targets, binding on nations to come up with certain amount of money? Binding in what way?

　　SETH BORENSTEIN: That's the key question.

　　Everyone says they want something binding, but it's sort of, what do you mean by binding? And that's one of the issues that's going to be hashed out here. It does involve lots of new money, billions of dollars, if not eventually trillions. It involves all these nations; 181 nations have made pledges: Here's what we're going to do individually.

　　Now the binding part is holding them to these pledges, a system to monitor these pledges, and perhaps, if you're not reaching these pledges, what do you do? And then it's all got to be designed so that it doesn't go through the U.S. Senate, because it can't go through the U.S. Senate because of American politics.

　　GWEN IFILL: And American politics means that that requires a two-thirds ratification in the U.S. Senate, and that's unlikely to happen.

　　I want to ask Michael Levi about what we have seen in the past. We have been to these meetings before in Cancun and in Rio and Kyoto and Copenhagen. Is this one any different?

　　MICHAEL LEVI, Council on Foreign Relations: I think this one is different.

　　I think it's different because we're starting to set realistic goals for what these summits can accomplish. We used to go to these expecting to take a global emissions cut that everyone needed to reach and negotiate over how to divide it up, then everyone would go home and execute that.

　　It was kind of like old-style arms control negotiations. I would get rid of this many missiles. You would get rid of that many. We would go home, we would do it. It turns out that climate change isn't like that. Leaders can agree to whatever they want, but actually changing the energy economy is incredibly difficult.

　　And it's a lot more like a domestic policy problem, a domestic politics problem than it is like a traditional foreign policy, national security issue.

　　So, what's different this time is that, instead of putting the burden on Paris to solve the problem, negotiators are asking, how can we build an international agreement that helps countries solve the problem themselves? How do we help them cut their emissions more deeply? How do we help them adapt to climate change?

　　I think that makes this fundamentally different.

　　GWEN IFILL: Would you say — Mr. Borenstein just talked about the money which has to be committed here. What would you say would be the potential major sticking point in the next 11 days?

　　MICHAEL LEVI: I think the biggest sticking point is likely to be over money.

　　When we saw the clash in Copenhagen six years ago, the ultimate turning point was over money. This is money that comes from wealthier countries to help poorer countries adapt to climate change, deal with the damages caused by climate change, and transition their energy economies.

　　And it speaks to a basic political reality, which is, if you're from a poor country and you go home from the climate summit, and you say, we have got some pledges, countries are going to take action in the next 10 years, and that's going to help us avoid dangerous climate change in the next 50, your people are going to look at you and say, what does that mean to me today?

　　If you come back with pledges of aid, in addition, then that's a stronger political proposition. If you look at the basic politics of how this works, it leads you to money.

　　GWEN IFILL: Seth Borenstein, we did hear, speaking of money, today we heard private sector giants with names like Gates and Bezos and Zuckerberg promise to make a commitment to a green energy fund. Does that change this in any way? Or is this something for the U.S. to trumpet?

　　SETH BORENSTEIN: This is something quite a bit different than in previous years.

　　You are seeing — and this has happened in the last couple of years, but it's especially happening now — private industry money, business is — they're stepping up and they're probably doing more than many countries, and that's helping.

　　They're seeing sort of the reality of the economics and climate change. And they're saying, if we're going to — if you're going to do something, let us volunteer, instead of you impose, and let us help do something with technology.

　　So, I mean, what you're looking at is both technology and business are dramatically different than, let's say, 1997 in Kyoto. Those are two of the biggest reasons why many people are optimistic this time, because the technology is so different, has improved so much, and your — and the business community, much of the business community is on board now.

　　GWEN IFILL: OK. Well, we will be watching all this very closely…GWEN IFILL: … as I'm sure you will too.

　　Seth Borenstein of the Associated Press and Michael Levi of the Council on Foreign Relations, thank you both.

　　MICHAEL LEVI: Thank you.

　　SETH BORENSTEIN: My pleasure.