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

Cities offer us powerful leverage on our most stubborn, wasteful practices. Long commutes in our cars, big power bills from our energy-hogging buildings, shopping trips to buy stuff that'll spend a few short months in our homes and long centuries in our landfills.

I think there's a gigantic generation gap in terms of how people understand the Internet and how much they think technology is an important factor in social change.

Cities generate most of the global economy, and most of its energy use, resource demands and climate emissions. How we build cities over the next decades will largely determine whether we can deliver a bright green future.

We have to craft new political realities, not only in places like India, Afghanistan, Kenya, Pakistan, but here at home as well. Another world is possible.

There's no law of physics that says we have to be an unsustainable society - in fact, quite the opposite. The planet's ready to work with us if we're ready to think differently, but we do have to make that jump and start to do things in new ways.

There’s more to being an environmentalist than occasionally signing an online petition and mailing your check to the Sierra Club. Really the most effective environmental actions you can take have to do with crafting your home and surroundings, your workplace decisions and your investment habits.