"Until recently, economists have not been particularly carried away with concern over environmental problems caused by industrial development. Just as in the other sciences, the few economists ...who have always sounded the alarm ...are somewhat out of the mainstream. These humanist concerns seem to have gone out of style after the age of classical economics. Even the conventional analytical models of contemporary economics seem to prefer to exclude these concepts by ignoring them entirely or by shunting them off into their own branch, called "economic externalities." These externalities include any “given” or windfall factor, such as the availability of transportation, technological know-how, a labor force, or resources, factors that are not themselves directly involved in the economic analysis of markets and businesses. For example, the regularly bright and sunny weather of Hollywood was considered an external economy of the movie industry there. The movie moguls, no matter how tyrannical, could neither turn on nor turn off the sun. But as the surrounding community grew and the smog thickened, the weather became an external economy. In very recent years concern over these economic externalities has grown. The environmentalists are beginning to be included in the mainstream. The literature is growing, and professional meetings include sessions on environmental economics. Attempts are even being made to extend the theoretical framework to include the changes in the environment caused by economic activity. [...] The Materials Flow of the Economy... sees the human race living on a 'space ship earth' in which all the inputs and outputs, all the original resources and all the final wastes, must be accounted for. Furthermore, when the materials are returned in the form of smoke, sewage, garbage, junk, heat, noise, and a wide variety of noxious gases, the world becomes a very changed place — and the change is seldom for the better. Implicit in this materials flow concept of the economy is that the less production that is needed to maintain an adequate level of affluence, the better. An efficient economy is one that gets big results with little effort. More industries, more mines, more businesses, more employment, and more consumer goods do not always mean more well-being... because all these also mean more destruction of our natural resources and despoilation of our surroundings."