Seven billion people presently are eating thanks to petroleum, natural gas, and other non-renewable fossil fuel resources used to cultivate, plant, irrigate, harvest, process, transport, and market food. Read Dale Pfeiffer’s Eating Fossil Fuels: Oil, Food and the Coming Crisis in Agriculture (New Society Publishers, 2006)
When affordable oil is used up over the next couple of decades when the global population may be nine billion), there is no scalable substitute that can replace it.
That may very well happen. As cheap petroleum gets used up I imagine we will see the militaries of the world begin to hoard and stockpile it for strategic use. China is already sewing up all the remaining contacts in Africa that it can get. Of course, if the military et al. get the oil, that will leave the working and soccer-mom population suddenly without fuel for their SUVs. The best off will be people within biking or walking or train and bus distance from work, church, hospitals, schools, shops. The worst off will be people in distant suburbs, for whom any errand is a car trip. They will begin to see their home equity plummet like stones. People within reach of public transportation or cycling and walking networks will see their house values skyrocket.