believed that energy and gross national product (GNP) were inextricably intertwined; today, we know that they can be uncoupled. At one time, most experts expected that oil prices would be two to three times higher than they actually are today. In recent years, energy systems have increased in efficiency and the supply of natural gas has been greater than projected.

The environmental effects of energy production and use occur on local, regional, and global scales. At local levels, energy production and use in autos, power plants, and industry are among the principal causes of urban air pollution, from particles to CO₂ to tropospheric O₃. Scientific understanding of the causes and developments of technologies have resulted in much-cleaner urban air.¹ Scientific understanding of the behavior of automobile emissions in the presence of sunlight illustrate the key roles of research and development in addressing environmental problems.

A particularly important part of the energy system at the local level is energy efficiency. A number of utility companies have initiated programs to improve the efficiency with which energy is used by residences, business, and industry. A number of technological advances in lighting, heating, cooling, and passive energy activities have also made it possible to keep energy demand constant without sacrificing lifestyle advances. In the case of transportation, automobile fuel economy has increased from 14.2 miles per gallon (mpg) in 1973 to 28.2 mpg in 1992—all through technological advances.

On the regional scale, energy production and use are the major factors in acid deposition. SO_x and NO_x emissions from power plants and NO_x emissions from automobiles are major contributors to acid deposition. Acid effects on aquatic