John Jeavons is talking about biointensive food production in cities --where half the human population now lives -- at a time when "farmer" is (he tells us) is no longer a job category in the US Census.
Some stats: 1/3 - 1/8 the water, 94-99% less energy per pound of food; biointensive can produce, 322 pounds of food from 200 square feet, enough wheat for a pound of bread a week from 300 square feet. In contrast, it takes 30k square feet to produce the current US diet. Jeavons says people can earn $3k/year from 100 square feet of biointensive minifarming.