mainly with strategies for abatement and costs thereof. The perspective of engineering, materi- als science, and environmental science is very different, of course. In this perspec- tive, transformation processes and attrib- utes are of fundamental importance. In this article, we adopt the latter perspec- tive, for the most part, while attempting to remain in touch with the former. The point of contact between the two perspec- tives is the conditions for development and adoption. Economists ask whether a technology is likely to be economically competitive in a free-market context. Engineers tend to look first for technical feasibility, then at cost. Engineering cost analyses are often criticized by econo- mists as being too optimistic in disregard- ing the “hidden costs” of innovation. Economic analyses are often criticized by engineers and scientists as failing to rec- ognize the potential for future cost reduc- tion as a new technology is adopted. Doubtless the argument will continue. We focus here on the materials perspec- tive as applied to long-term sustainability. There have been many definitions of sus- tainability, but we need not adopt any one of them. On the contrary, it is suffi- cient for our purposes to note that the extraction and dissipative uses of most materials, especially rare and toxic metals, are clearly unsustainable. There are two reasons. The first is that known reserves and probable undiscovered resources of a number of important metals are severely limited. (We do not argue that reserves will be exhausted in the next few decades, but neither can it be assumed that future supplies are unlimited.) The second rea- son for unsustainability is more urgent: It is that the assimilative capacity of the earth’s environment is limited. In some regions, the state of the local environment is already severely damaged. In the case of rare and toxic metals, environmental damage occurs not only as a consequence of dissipative usage— the buildup of cadmium in topsoil is an example—but also as a consequence of mining and smelting operations. The Materials and the Global Environment: Waste Mining in the 21st Century Robert U. Ayres, John Holmberg, and Björn Andersson MATERIALS CHALLENGES FOR THE NEXT CENTURY MRS BULLETIN/JUNE 2001 477 Background Sustainability is supposed to be the watchword of the coming century. Kenneth Boulding 1 characterized the eco- nomic system of the 19th century as a “cowboy economy,” meaning that re- sources were essentially not a limiting fac- tor. In contrast, he noted that in the future we must prepare to live in a “spaceship economy,” adopting Barbara Ward’s famous metaphor of “Spaceship Earth.” 2 In a spaceship, all materials must be recy- cled (or discarded into space). On the earth, the goal of total recycling or “zero emissions” is obviously a very distant one. Even the biosphere has not achieved it. Yet, for some materials, especially cer- tain metals, this goal must be taken seri- ously, even in the fairly near term. The relationship between materials and the environment in the coming century can be considered from two very different perspectives. The economic perspective sees materials as consumables and—to some extent—as wastes and pollutants, but always as abstractions, lacking in dif- ferential physical attributes. Resource eco- nomics concerns itself with availability and/or scarcity and the implications for economic growth. Mainstream economics considers materials hardly at all, being concerned with capital, labor, and “tech- nical progress,” the latter being measur- able only in terms of increasing factor (especially labor) productivity, of exoge- nous origin. In mainstream economics, scarcity hardly exists (in free competitive markets) except as an abstract cause of price increases and a possible inducement to innovation. Environmental economics considers materials essentially only as wastes and pollutants, and concerns itself seriously degraded landscapes around the copper-nickel smelters in Sudbury, Ontario, or the copper smelter at Butte, Montana, illustrate the latter problem. While not posing any major toxicity problems, the use of major abundant ele- ments such as aluminum and iron may also seriously affect the environment by the sheer size of mining, smelting, and refining operations. However, the buildup of a more sus- tainable industrial society comprising a larger share of a growing world popula- tion will also require an increased use of a range of metals. As an example, one of the major technological challenges of the cen- tury will be the transformation of the ener- gy system to reduce its environmental impacts, most notably climatic change due to global warming. Limiting human- caused climatic change will require a rapid diffusion of a range of new tech- nologies that can transform and use ener- gy more efficiently and of technologies that can supply energy without increasing the concentration of carbon dioxide in the atmosphere. Many technologies with the potential to contribute to such a transfor- mation, such as solar photovoltaics, low- emissivity and electrochromic windows, batteries, and fuel cells, are based on advanced materials of which many make use of rare and toxic metals. As another example, an increased use of a lightweight metal such as aluminum could decrease the energy intensity of transportation. The bottom line of this reasoning is that we may need to seek a range of new oppor- tunities to minimize society’s materials losses. One such opportunity is waste min- ing. The more our economy recycles and recovers useful metals (and other materials) from its wastes, the less mining will be needed and the less environmental damage will result from waste disposal. We now consider three specific opportunities. Coal Ash Coal is burned in enormous quantities: approximately 3.3 billion tons in 1998, supplying a quarter of the global energy demand. The main waste from coal com- bustion is carbon dioxide, making it a great contributor to global warming. This fact does not necessarily disqualify coal from taking part in a more sustainable energy system. Gasification of coal fol- lowed by a water shift reaction results in two pure gases: carbon dioxide and What’s a mountain got that a slag pile hasn’t? —Jean Giraudoux (1882–1944) The Madwoman of Chaillot, Act 1 The environment makes up a huge, enormously complex living machine that forms a thin dynamic layer on the earth’s surface, and every human activity depends on the integrity and the proper functioning of this machine. —Barry Commoner The Closing Circle, 1971 Materials Challenges For The Next Century presents a series of articles speculating on the role of materials in society in the coming century and beyond. www.mrs.org/publications/bulletin https://doi.org/10.1557/mrs2001.119 Downloaded from https://www.cambridge.org/core. IP address: 54.163.42.124, on 26 May 2020 at 17:24:28, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms.