Not everyone agrees that vertical farms will be economically viable. The biggest concern is energy. As with all indoor grow operations, artificial lighting like fluorescents or the LED's shown here must be supplied for any plant life that isn't exposed to sunlight.

Proponents insist that the reduction of farm equipment needed for harvest and transport would make up the difference by cutting back on fossil fuels. Some even argue that vertical farms could save energy by recycling wastewater and composting non-edible plant material to generate methane energy.

But most scientists agree that further studies are needed before we can know for sure whether these farms are feasible.