For the first time in recorded history, the majority of the world's population is living in cities.

"It's a wake-up call," said Ron Wimberley, distinguished professor of sociology at North Carolina State University. "It's always been assumed that rural areas will always produce what they're supposed to produce: natural resources, food, fiber, water, air, timber -- the things that are our daily basic needs."

"But if we keep extracting all the good things out of these areas and then dumping the bad things like pollution back on them without giving anything back, we're going to be heading for some big problems," Wimberley said.