The planet's biggest problems have to do with sustainability, environmental decline, global poverty, disease, conflict and so forth. Really, they're all interconnected - it's one big problem, which is that the way we're doing things can't go on.

To be young and aware is to know you’re being lied to; to know that a bright green future is possible; to know that we can reimagine the world, rebuild our cities, redesign our lives, retool our factories, distribute innovation and creativity and all live in a world that is not only better than the alternative, but much better than the world we have now.

If mass media, social isolation in the suburbs, alienating workplaces and long car commutes create a bunker mentality, the Internet does the opposite.

Copenhagen has done a remarkable job creating streets that are focused on bicycles and pedestrians.

I think we're going to start to see a new model of civic advocacy where people get together once in a while to protest, but it's more about an ongoing, sustained engagement in issues, networks and communities about which people care.

Urban retrofitting: creating different sorts of spaces and uses out of places that are already there.

You don't change the world by hiding in the woods, wearing a hair shirt, or buying indulgences in the form of 'Save the Earth' bumper stickers. You do it by articulating a vision for the future and pursuing it with all the ingenuity humanity can muster.