Vertical farming

http://science.howstuffworks.com/conservation-issues/vertical-farming.htm

Summary - idea is to do farming in buildings in urban areas. This could be the future of farming as most of the world's population is moving to urban areas and arable land decreasing in percentage. Since farming is carried out indoors, conditions can be controlled.

"Dr. Despommier believes that 150 30-story farms could feed all of New York City. Elegantly designed, these vertical farms would be carefully placed around a city or clustered together in a nearby development (in the case of New York City, possibly on Governor's Island). They would remain unobtrusive, or even pleasant to the eye."

Article has pointers to more information as well.