 Our buildings consume about 40% of our energy. And with our emissions threatening to permanently change our climate, we need more efficient, better, greener cities. We can start by being smarter with what we have – passive solar buildings, public transit, private petal power, high-density living and teleworking. But our food production is still a long way from most of the people in the cities built on the best arable land. Vertical farming could turn this on its head or at least its side. It would bring together a host of emerging technologies by putting food production on the buildings we live and work in to reduce land use, cool our urban heat sinks and drastically reduce food transport costs. Modern agriculture uses 70% of the world's available fresh water but vertical farms could be fitted with nanofilms that boost condensation and nanomembranes that would filter and clean recycled water. Better water quality, less waste. Crop effectiveness would be boosted by genetic engineering to select the best genetic variants for the environment. Fibro-optics might provide light with incredible energy efficiency. One square block farm, 30 stories high, could yield as much food as 10 square kilometres outdoors. There are of course hurdles. The crops best suited to vertical farming may require us to adjust our diets. But would farmers and agribusiness take this lying down? Or is it simply that our dollars are best spent on smart, simple and practical improvements to existing infrastructure and technology?