With regards to your comment on 1% of people being farmers and that being adequate, here's some fast facts about the US agricultural industry:
(1) 300 million people in the US, and the US can sustainably produce food for only 130 million of them. (recentish UN estimate I believe)
(2) Many US farms are net energy consumers, ie. they burn more energy in production than they give people in food.
Second, the earth will actually produce enough to support many humans using no humans (ie. "let the plants grow back, stop maintaining the concrete, stop unsustainably exploiting and poisoning the environment"). It just requires us to be a bit more in tune with the environment (eg. decentralize, consume in-season, eat less meat, start sharing a bit more).
Interesting times.