I am delighted at the spirited discussion my question has provoked, and had I known it would I would have taken more care when writing it. Andrew, love the new transport infrastructure idea. Anna, Lindon, Marcus, vertical farms rock. Ron, I disagree.

The cities do not subsidise rural infrastructure! Our political/economic system does. I would suggest that more infrastructure subsidy goes into cities than into country. "Isn't it time to move on?" is a totally irrelevant and pointless question when people are struggling with the here and now.

response to Andrew Nelson: I don't think the questioner is deluded to think that we can grow wheat (at the scale required) through vertical agriculture. If we were even able to grow only 50% of the produce (say mostly vegetables and some fruit) we would dramatically reduce the amount of energy needed to transport foodstuffs to our cities. This type of agriculture could assist to reform our cities and make them more interesting, dynamic, sustainable and resilient places to live.

vertical farming could prove incredibly cost effective - imagine the end of "seasonal" foods, no exposure to disease, no pests (nor pesticide), no need for massively polluting infrastructure, and every single crop would be a bumper crop. Of course the vertical nature of the farm could extend in either direction, up or down. So if you're worried about colossal skyscrapers blocking out the sun imagine foods arriving from the ground via some sort of conveyer belt instead.

The idea of vertical farming has been around for a long time Gilbert Ellis Bailey wrote a book about it in 1915, and its about time we give it some serious thought now that we have the technology to make it a practical reality. Subway systems were considered a controversial issue at the time because of the cost, many considered them unnecessary but can you imagine what large cities around the world would do without them today? Investment now will save the future.

Sorry but I think you are kidding yourself if you think we can ever efficiently vertically grow enough wheat, oats, canola etc. to meet our city demands. Fresh tomatoes and herbs maybe, but grain crops I think highly unlikely. And we're just starting to appreciate less intensive farming of animals, so let's not move towards vertical pig, sheep, cattle and chicken production. More intensive aquaculture I agree with. We just need to solve renewable energy transportation. I think the solution will lie in actually building a new kind of transport infrastructure using automation, renewables and smaller volume/local processing to deliver smaller packets of produce more frequently rather than a semitrailer load at a time.