Here’s a great story from The New York Times about China’s relocation of 250 million people from the countryside to cities.
In terms of great, big challenges, how we manage our cities (and populations) in the future is near the top. The greatest opportunity to control for the health and future of the world is actually in cities; that’s where the majority of resources are consumed (from the natural world), and that’s where all of the carbon is produced. If you care about the environmental and health, then you have to care about cities.
At a local level, we’ve been fortune to work on this issue for several years now with some thoughtful organizations, EcoDistricts (they do important work), Gerding Edlen (one of the world’s main green builders; see Mark Elden’s great TEDxPortland talk) and the Portland Development Commission, which is leading the reboot of the We Build Green Cities campaign.
These folks are all on the cusp of very big impacts.