By 2050, the world's human population will probably have risen above nine billion, but it will also be on the verge of stabilizing after two centuries of explosive growth. Before us lies 40 years in the wilderness; beyond 2050 lies what we have to hope is a promised land. Getting there will take not just technical solutions that make life on earth sustainable; it will take a sustaining vision of our place on the planet.

The 2011 Aspen Environment Forum, in conjunction with National Geographic, explored the shifts in thinking and imagination that will be required to rise to the awesome challenge, from ways of reorganizing urban ecosystems, to preserving biodiversity and providing a stable climate, clean air, clean water and food for a growing global population.