Background: At the beginning of human history, we had to satisfy our energy needs (for food, heat and movement) by using our own muscle power and gathering or hunting naturally available plants, animals and wood. Each stage in the evolution of human society (the development of farming, domestication of animals, harnessing of wind and water power) increased the average per capita energy use, but it was the Industrial Revolution and the exploitation of fossil fuels which marked the transformation of societies into the energy-intensive economies ....