From the Economist:

The world’s population is expected to increase to 9.1 billion by 2050. Feeding all those people will mean increasing food production by 70 percent.

Why not create more agricultural land by building upwards?

Such is the thinking behind vertical farming. Skyscrapers filled with floors of orchards and fields, producing crops year round, will sprout in cities across the world.

The use of pesticides, herbicides and fungicides can be kept to a bare minimum by growing plants indoors. Soil erosion won't be a problem — the food will be grown hydroponically.

Sci-fi dreams of fields in the sky?

See the Economist for the complete article.