Humans have a knack for reproduction. By 2050, the world population is expected to reach 9 billion people, nearly doubling global demands on food and livestock feed. But there's one major problem: Farms can't keep up.

Until now, humanity's rapid population growth has been countered by the "green revolution"--advances in pesticides, fertilizers, and the genetic modification of crops. But no matter how much we maximize crop yield per acre, the limiting factor for food production is land. And farms use a lot of it.

But if we can't build out, why not build up? Vertical farms, like the one pictured here, are a proposed innovation that might allow us to do just that. While they're still in the planning stages, these "skyfarms" could revolutionize our agricultural system.