Peak Oil
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.