Deep walkability describes a city that is built in such a way that you can move from one area to another on foot, on bicycle, on transit and have an experience that remains a pleasant one, that you feel you are welcome not just in the neighborhood but moving between neighborhoods.

We get so little news about the developing world that we often forget that there are literally millions of people out there struggling to change things to be fairer, freer, more democratic, less corrupt.

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.

At its very heart, Worldchanging is about using the best of people's new ideas, bringing them together and applying them to the massive problems that we all face.

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.

Clean air and water, a diversity of animal and plant species, soil and mineral resources, and predictable weather are annuities that will pay dividends for as long as the human race survives – and may even extend our stay on Earth.

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