Energy is not as it always was. Yesterday’s world was entirely dependent on biomass, particularly wood for heating and cooking. Even as late as 1900, biomass satisﬁed half of energy demand with much of the remainder satisﬁed by coal. Natural gas was still in its infancy stage as a source of energy for lighting and heating as was hydro for generating electricity. Oil was still primarily a fuel for lighting (kerosene) and the automobile age was just beginning. Nuclear had its beginnings in the Second World War and renewables (solar and wind) in the late twentieth century.