ABSTRACT
Energy is basically a physical variable— measured variously as calories, kilowatt-hours, horsepower, British Thermal Units, joules, and so forth. After about a decade of “moderate” energy prices, in mid-1990 a rapid and significant increase in oil prices began that continued in the first decade of the twenty-first century. By avoiding price controls, rationing, and energy-allocation policies of the 1970s, government energy policy was focused on responding to market imperfections and breaking down regulatory barriers. Geopolitical relations and conflicts as well as internal social and environmental conditions, play a role in how the energy mix shakes out. Although energy supplies are thought to be less constraining now than in the 1970s, environmental problems caused by the present energy system are more severe and getting worse. Fundamental to understanding the energy flows of both ecosystems and human social systems, autotrophic plants transform solar radiant energy into stored complex carbohydrates by the process of photosynthesis.
