Energy Leverage in Agriculture
While human beings lived as hunters and gatherers, 500 calories of human effort yielded 2000 calories of food produce. Until the industrial era, farming was still a net producer of energy. Today the food system has turned into a net user of energy, as it takes 7-10 calorie of fossil energy to produce 1 calorie of food produce. When fossil fuel runs out (during lifetime of most of us alive today) the effects will be felt on food production and supply.