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design, greater utilization of waste heat, more efficient transport systems, and improvements in conversion efficiencies by use of fuel cells, magnetohydrodynamic facilities and other devices.

Economic technology can be expected to affect demand curves for other mineral materials too. As the cost of metals rises, secondary recovery will increase and there will be pressure to use metals in

ways that improve the economic practicability of salvage and recycling; thus the potential demand for new or primary supplies of metals will be lowered. Consideration is even being given to the reclamation and reuse

of certain nonmetallic commodities, such as foundry sand.

Provident technology can affect demand curves even more strongly than economic technology, but its advent and impact are much more difficult to predict.

What all this means is that demand curves for a single resource should be multiple, reflecting a range of cost and technological forecasts.

Demand curves are related to depletion curves. During the period of national self-sufficiency in a specific mineral resource, the demand curve and the depletion curve are essentially identical: domestic production equals domestic consumption. When, however, rising costs of domestic production bring about recycling, importation or substitution, the domestic primary production no longer will equal total domestic consumption. At that point domestic depletion becomes much more difficult to forecast because now forecasts must reflect estimates of the portions of the total demand that will be satisfied by imports and secondary material, as well as the impact on demand of the use of substitute materials.

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The relation of technology to depletion

Economic technology

Technology plays two roles in the development and utilization of nonrenewable resources. It can increase the efficiency of the exploitation system, thereby extending the amount of work to be gotten from a finite amount of the resource; at the same time it extends the reserves of that resource by making it profitable to exploit deposits previously too lean or too deep to be counted as reserves. This economic technology has increased enormously the amounts of copper and aluminum that have entered our industrial society, as well as the amount of work the society has been able to recover from burning the fossil fuels. For several decades, early exhaustion of petroleum reserves has been forecast, but new discoveries and improved economic technology have kept production increasing and reserves adequate.

Economic technology works to extend reserves, reduce demand, and increase utility. It is economic technology which has cut in half, over the last 40 years, the amount of electricity required to produce a pound of aluminum and which has reduced the grade of minable copper-bearing rock from about 2 percent to 0.6 percent in the same period.

Provident technology

The second role of technology involves invention and design of exploitative systems that create new resources out of previously worthless material and result in abrupt large increases in resource reserves; this provident technology has created great additional reserves of aluminum and iron, and is in the process of creating new energy reserves out of tar sands, oil shale, and uranium and thorium

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deposits. Domestic uranium reserves may increase by 60 or more times when the fast-breeder reactor becomes practicable and starts to produce electric power for public consumption.

Provident technology works to create new resources by discovery

of new uses, new recovery and processing methods, and new energy conversion devices. It frequently increases demand for one material while decreasing the demand for one or more other materials. It was provident technology which first made aluminum available as an economical construction material by invention of the electrolytic process for recovery of the

metal from its ore; it was provident technology which created the vast reserves of the low-grade copper deposits by invention of the metallurgical process known as flotation.

Limits of technology

The current controversy about "limits to growth" insofar as it involves nonrenewable resources reveals two strikingly opposed concepts of the potential of technology to extend resources.

The cornucopian view is that resources are defined by economics and not by physical limits, and that the so-called nonrenewable resources are essentially unlimited because they are continuously being created by technologic discovery and improvement powered by the forces of the economic system. Proponents of the cornucopian view state categorically that the law of diminishing returns does not apply to mineral resources and that scarcity of such resources is a myth promulgated by "prophets of doom".

The opposing view, often termed Malthusian, is that mineral resources are indeed scarce and will become more so, that the law of diminishing returns does apply to them and to technology as well, and that the

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"prophets of progress" are basing their case on a misreading of history, lack of understanding of physics, and unwarranted faith in technology.

Because these contrasting viewpoints strongly color the consideration of strategies necessary to protect the nation from decreased availability of vital resources, they will be referred to again further along in this paper, in more specific contexts. But first, a brief historical outline of man's use of natural resources may be helpful in attaining perspective for the later discussion.

Historical sketch of nonrenewable-resource use

A brief history of man's use of nonrenewable resources will serve to indicate the recency of his dependence upon them and to suggest certain relations between population, living standards, and the use of nonrenewable (especially energy) resources.

Our industrial-technological society was built on the use of nonrenewable resources and operates by increasing consumption of them. Although the semi-industrial society that grew up in western Europe in the late Middle Ages and during the Renaissance was based on the renewable resources of agricultural food, water power, fuel wood and wind power, our present industrial society got its great impetus with the discoveries that led to power production from coal through the steam engine and process heating from coal through coke. Thus was ignited the Industrial Revolution, which divided the world into the haves and have-nots. The haves were those who controlled inanimate energy in

sufficient measure to produce goods and services in such abundance that ability to consume for the first time in man's history became a social

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For most of man's history as an identifiable species, he has relied on renewable resources to sustain his communities (Fig. 4); only during the past 150 years have systems emerged based largely on the use of nonrenewable resources.

For about 90 percent of man's existence his only source of energy was the wild food he captured, gathered and ate. For only about 10 percent of his brief history on earth has he had fire; for most of that time he burned wood for heat and used animal pelts for clothing. For only 1 percent of his history has he planted and harvested food crops, milked, butchered, driven and ridden domesticated animals; during his early agricultural days he made some use of metals, clay, and building stone, but his resources were still dominantly food, fiber and wood. For only 0.1 percent of his terrestrial tenure has man used wind and water power to any great extent; his sails were made of cloth or skin and his boats and windmills were built mainly of wood. In this period he began to use nonrenewable resources such as stone, clay, iron, copper, tin, and the precious metals, for buildings, monuments, tombs, roads, tools, weapons and jewelry. Only in the latest 0.01 percent of man's history has he switched his energy base from renewable resources to the nonrenewable fossil fuels and fissionable uranium, and has he greatly expanded his use of iron, cement, and other construction and manufacturing materials.

The Industrial Revolution made coal and iron the basis of a new society, a society characterized by rapidly increasing consumption of nonrenewable resources and a rapid increase in population.