Cabbies in particular seem to like discussing the fate the Earth.

It's not just enough to survive. We've got to make something better than what we've got.

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.

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.

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

The denser places get, the lower the amount of energy people use to get around it.