Inspired by The 11th Hour, we brought a panel of leading scientists and activists to New York City to tell us how we might heal the planet. The participants were urged to move beyond bleak diagnoses, to offer concrete proposals for a sustainable future. The conversation -- often spirited -- ranged from how to impose a tax on carbon to the design of walkable, bikeable communities to the challenges of motivating political leaders and the public to act.

An edited transcript of the conversation runs begins below, accompanied by video.

Kolbert: What would a sustainable world look like?

Schmidt: It's going to take a 60 to 70 percent cut in carbon emissions -- that's a huge number. It's a number that doesn't take into consideration the increase in emissions resulting from industrialization in China and India and the rest of the world, so these are really, really challenging numbers. It doesn't all have to be done tomorrow. But to keep carbon dioxide at a level that, we hope, won't be too detrimental to the climate system, the necessary changes have to be in place relatively soon, functional by, say, 2050 or 2060, but certainly by the end of the century. After that we're going to need to bring the numbers down even further.

Gelobter: I can't stand it when we say how hard it's going to be, because it takes such a lot of work -- and money -- to put that much crap up there. We're waging a $2 trillion war in Iraq. At least a third of that war is about oil, if not more. With that money alone we could probably cut emissions worldwide by 30 or 40 percent. So I think it takes a lot of bad stuff to put all that bad stuff up there.

Schmidt: The problem is, a lot of good stuff is also creating this problem: the energy we're using in this studio to record this conversation, the energy that powers the subway system. We have power stations all over the world that are a third of the problem.

Gelobter: But we can get energy in much healthier ways.

Orr: To make the transition to healthier ways, to renewable energy and efficiency, will mean reconfiguring a lot of things -- that's a world of front porches, bike trails, local farms, a very different kind of world. It's probably not a world of big box stores.

Schmidt: We started off talking about sustainability and climate change, and now Michel has brought up the war, you're bringing up big box retailing -- these are frankly kind of external issues, which, I agree, are connected in some profound way, but mingling them all up doesn't take us any closer to finding a solution. It becomes one vast problem and you think you have to solve everything to make any progress.

Orr: Gavin's point is exactly right. If we try to take on the whole thing, it's too daunting and we just paralyze ourselves. One question is, how do we motivate the public? How do we help them feel that it isn't all just insurmountable? I think the environmental movement has to do a better job of portraying a world that it's possible to build, a world that is different and captures the public imagination. At the same time we need to watch what some people in the environmental movement call happy talk -- it's all going to be easy, just screw in better lightbulbs and buy a Prius. The fact is that sacrifice is part of where we're headed. When Winston Churchill said in 1940, "I have nothing to offer you but blood, toil, tears, and sweat," he was being straight with people. That will work for us, too, if we have the courage to deliver the news.

Gelobter: We have to show people what the carbon-light lifestyle is. It's one where you live near your school, you live near your job, you go see your kid at lunch sometimes, and you pick up your wife on your way home from work. That's a life we all want. It's a life we can have, and it's a life the fossil fuel system is actually keeping us from having.

Kolbert: How do we make the changes you're talking about?

Gelobter: Pay the costs of climate change in the fuels we buy.

Kolbert: How?

Gelobter: A carbon charge, a fee for use of the atmosphere, an auction of carbon permits.

Kolbert: Federally imposed?

Gelobter: We could start with the states. It's going to be hard to get to the optimal solution quickly in Washington. When you look at the Clean Air Act, it took a lot of states nipping at the heels of dirty polluters for 30 years. Some states are already adopting very aggressive standards that will start industries thinking twice about how they operate.

Schmidt: I think this combination could work: a carbon charge that taxes things we don't want in connection with subsidies that do the things we want. Right now we subsidize emissions of carbon dioxide, and we penalize people who conserve energy. That's a mistake.

Kolbert: Let's talk political realism for a second. Although Michel carefully avoided using the "t" word, a carbon charge is going to get characterized as a carbon tax, so it faces an uphill slog.