The shift to alternative energy sources may be gradual as fossil fuels continue to be used, or it could be accelerated by concern about potential environmental effects of burning fossil fuels. Regardless of which path we take, one thing is certain: Fossil fuels are finite. It took millions of years to form them, but they will be depleted in only a few hundred years of human history.
Using even the most optimistic predictions, the fossil fuel epoch that started with the Industrial Revolution will represent only about 500 years of human history. Therefore, although fossil fuels have been extremely significant in the development of modern civilization, their use will be a brief event in the span of human history. Energy consumption in the United States in the year 2050 may be about 160 exajoules.
What will be the energy sources for the anticipated growth in energy consumption? Will we follow our past policy of business as usual coal, oil, nuclear, or will we turn more to alternative energy sources wind, solar, geothermal? What is clear is that the mix of energy sources in 2030 will be different from today’s and more diversified. All projections of specific sources and uses of energy in the future must be considered speculative.