Alex Steffen has long supported urbanization and the sustainable development of cities as a key climate solution -- as a founder of the very influential but now-defunct World Changing, he's argued that if we're smart about it, the world can become a greener place as its billions of residents move into metropolises. In the sharp TED talk above, he explains how and why this is the case.It's really not difficult to understand the core principle behind all the cool design slides and the futuristic trappings that come along with imagining a world filled with mega-cities: When people live closer together, they emit less carbon and less pollution. Things are more easily obtained, and more easily shared.
This principle is also the backbone of his carbon zero cities project, which is much more elaborate, but essentially born of the same ethos. Anyhow, if you're looking for an informed, entertaining explanation of why so many greens are huge urbanization proponents, this should do the trick.