As a 600m tall vertical greenhouse shaped like the wings of a dragonfly is proposed to sit in a river in New York by Belgian designer Vincent Callebaut, let's look at the urban farming solutions that could be closer to home (and completion).

Experts predict that by the year 2050, nearly 80% of the earth's population will reside in urban centres as the human population will increase by about 3 billion people during the interim.

But as we build more and more cities and neglect natural land, where will the crops that feed us everyday find a place? Vertical farms like the one above one, designed by Chris Jacobs, are tipped to be the answer by researchers at Columbia University, but what are they?