Figure 13.1 shows the competitive struggle among the five main sources of primary energy as a dynamic substitution process. Fuelwood and traditional energy sources dominated primary energy until 1880. Coal, the major energy source between 1880 and 1960, was the basis for the massive expansion of railroads and the growth of steel, steamships, and many other sectors. Since 1960, oil has assumed a dominant role at the same time as the automotive, petrochemical, and other industries have matured. The current reliance on coal in many developing countries illustrates the gap between the structure of primary energy supply and actual final energy needs.
Smooth lines represent model calculations and jagged lines are historial data.
During the past two centuries, global consumption of primary energy has increased about 2 per cent per year, doubling on average about every 35 years. As a result, emissions and other environmental effects of energy conversion and end-use have also increased. Most of the anthropogenic atmospheric CO 2 is due to fossil energy use and deforestation. Fossil energy consumption contributed more than two-thirds of all human sources of CO 2 . In general, the instrumental determinants of future energy-related CO 2 emissions can be described by the Kaya identity.