Since the discussion is currently about north africa I am going to point out an interesting company currently building things there:
http://www.seawatergreenhouse.com/
What this does is turn a patch of desert, which has extremely low biomass, into an extremely high yield agricultural production area. The inputs are steel, glass, and labour and modest amounts of electricity, and if it becomes nessesary, this will scale to feed any number of humans the planet will ever see, forever.