Michael Brune, I want to start with you and ask you what overall you see as the significance of the president's visit to the Arctic.

　　MICHAEL BRUNE, Executive Director, Sierra Club: Well, it's very significant. The president has made climate change a top priority of his administration in both terms.

　　And going to the Arctic is a great place to showcase the threats that climate change has, both on the economy, as well as the environment, because there is no place that is warming faster than the Arctic anywhere else around the world.

　　GWEN IFILL: Robert Bryce, what's your take on that?

　　ROBERT BRYCE, Senior Fellow, Manhattan Institute: Well, I can't argue temperature issues.

　　I think what's interesting, though, is that the president has given the green light to Shell to drill in Alaskan waters, and I think it's a pragmatic move. While he is talking about climate change, there is a conflict between some of those climate change discussions and what he said Saturday in his radio address. He said, our economy still has to rely on oil and gas. As long as that's the case, I believe we should rely more on domestic production than on foreign imports.

　　And I think that that's a positive move, and clearly the oil and gas sector has been one of the true bright spots in an otherwise lackluster economy during his presidency.

　　GWEN IFILL: Michael Brune, is it fair to the president, to the White House to judge his environmental record by this decision on drilling, or is that actually a dark spot on another — on a record in which he's reducing greenhouse gas emissions and taking other actions?

　　MICHAEL BRUNE: I think it's fair to say that the president has done a lot on climate, and it's also fair to say that his record is far from perfect.

　　One of the things that the president has done has been able to help us to curb our oil consumption by making our cars and trucks and all vehicles more fuel-efficient. He's also begun to lead us away from coal in the production of electricity and natural gas and to shift more towards clean renewable energy.

　　But drilling in the Arctic is just the wrong way to go, and it threatens to undermine a lot of the progress that the president has made.

　　GWEN IFILL: Let me ask Robert Bryce about that, because you see it as an unalloyed good.

　　But we did a story not too long ago on this program about the oil glut, about the increase in shale production.

　　ROBERT BRYCE: Sure.

　　GWEN IFILL: Why is there a need for additional offshore oil drilling in Alaska?

　　ROBERT BRYCE: Well, I will make a quick point.

　　And one is that Alaskan energy has been a strategic issue for the U.S. now for close to a century. Remember, it was 1923 when President Harding designated the Naval Petroleum Reserve in Alaska. So, this idea of Arctic drilling is hardly new. The Arctic National Wildlife Refuge of course has been a flash point now for decades, but we have been drilling in Alaska for decades, for the most part very safely.

　　But as far as the broader gain here I think that the president is looking toward as well is the enormous amounts of recoverable energy resources in the Arctic. The Department of Energy estimates them at something on the order of 400 billion barrels of oil equivalent in natural gas and oil. That's four times the crude oil reserves of Kuwait.

　　So for the U.S. to just forgo the Arctic resource at this time, I think it would be a big mistake.

　　GWEN IFILL: Let me let Michael Brune respond to that.

　　MICHAEL BRUNE: Yes, thanks.

　　So, drilling in the Arctic might have been a good idea back in 1923, but it's 2015. The world has changed, and we should change with it. Scrambling with Russia to race to see who can drill in the Arctic first is like racing to see who can light the fuse on a time bomb.

　　You know, supremacy in the Arctic shouldn't be defined by who gets to destroy it first.

　　GWEN IFILL: Go ahead. Go ahead.

　　MICHAEL BRUNE: Well, I was going to say, we have an ability right now to rebuild our economy in the 21st century and do it in a way that doesn't poison our air, doesn't poison our water, doesn't put our entire climate at risk.

　　And that is by investing in clean energy, which I will say to Robert is growing at a much faster rate than the rest of the economy, particularly the oil and gas industry.

　　MICHAEL BRUNE: Sorry. Go ahead.

　　GWEN IFILL: Well, I was just curious. I want to ask you both this.

　　ROBERT BRYCE: Sure.

　　GWEN IFILL: Is there a reason why those two things can't coexist; that is, increased drilling and increased clean energy and reducing emissions and reducing dependence on coal? Why isn't that — why can't that all work together for good?

　　I will start with you.

　　ROBERT BRYCE: Well, I will make two points.

　　One is that natural gas has been a critical part in the U.S. reducing CO2 emissions. The Sierra Club is anti-fracking. Natural gas displacing coal in the domestic electric generation sector has been a key factor in the fact that the U.S. has reduced its CO2 emissions by 500 million tons over the last decade alone. It's more than any other country in the world, including Germany.

　　Further, if we're serious about clean energy and serious about climate change, we should be serious about nuclear energy. The Sierra Club is adamantly opposed, has been adamantly opposed…

　　GWEN IFILL: Well, let me let The Sierra Club respond to that.

　　ROBERT BRYCE: … since 1970, even though nuclear is reducing CO2 emissions more than any other form of energy.

　　GWEN IFILL: Mr. Bryce

　　MICHAEL BRUNE: Sure.

　　Well, how about I state the Sierra Club's policy? We look at all energy sources with a few different criteria. What's the cheapest, what's the cleanest, and what can come online the quickest?

　　And what we know is that nuclear power actually ranks dead last in all of those categories. What we also know is that clean energy is dropping in cost as it increases in installations. The more clean energy that gets installed, the lower the costs get, whereas fossil fuels are becoming more and more expensive, with the current exception of oil right now.

　　What are seeing across the United States is that, increasingly, communities are moving past coal, beyond natural gas and, in some cases, beyond nuclear power. Investing in energy efficiency, investing in solar and wind, they are cutting costs, they are saving rate-payers money, and they're helping to stabilize the climate and reduce air and water pollution.

　　What is not to like about that? We can build an economy on clean energy. We shouldn't be investing in dirty oil, particularly from the Arctic.

　　GWEN IFILL: Do I see an agreement coming from the other side there?

　　ROBERT BRYCE: Well, look, there is no question I'm adamantly in favor of natural gas.

　　As I said, it's been a key factor in the U.S. reducing CO2 emissions. But the hard reality is what the president said. We need oil and gas. Globally, there are one billion automobiles. We have roughly 400,000 airplanes, tens of thousands of boats. All of them run on oil. The idea that we're just going to quit using oil is simply not true.

　　The Sierra Club has been spinning this idea that we can just run the world on renewables. It's simply not true. It hasn't been true, won't be true. We need oil and gas.

　　GWEN IFILL: Well, I don't think that's necessarily what the president is saying, which is what we are talking about today.

　　But we're going to leave it there for now.

　　Robert Bryce of the Manhattan Institute and Michael Brune of The Sierra Club, thank you both very much.

　　ROBERT BRYCE: Thank you.

　　MICHAEL BRUNE: Thanks for having us on.