Material intensity of use (IU) refers to the quantity of material used to produce goods and services. Intensity of use often is intended to be a summary measure that links the use of a material(s) to trends in the output of an industry, sector, or economy. Empirical measures of IU are derived from the accounting identity that defines the consumption of a specific material i (Xi):
- where Y is the output of industries that consume material i, and GNP is the total output of the economy. Intensity of use typically is defined as the ratio of materials use to value added, which in the case of an economy is equivalent to GDP;
- The majority of analyses of IU measure X in physical units (weight or volume), and aggregate different materials on this basis. This raises a number of important conceptual and methodological issues which we return to in later sections.
Intensity of use is determined by two quantities. The first term on the right hand side of (2) is the material composition of product which reflects changes in the mix of materials used to produce individual goods. The second term is the product composition of output, which reflects changes in the mix of goods produced by the economy.
Changes in these two factors, and hence changes in IU, are determined by a number of social, economic, technological, institutional, and environmental forces. Those identified in the literature include:
- Technical improvements that decrease the quantity of materials used to produce a good or service. Well-documented examples include metal use in the beverage container industry, materials use in automobile manufacture, and communications. Technical changes that improve material efficiency include not only advances in engineering and materials science, but also in the organization and management of production itself, such as computer-aided production processes and just-in-time production.
- Substitution of new materials with more desirable properties for older materials. Four categories of inter-material substitution are: (a) cost-driven (aluminum for copper in electrical conductors), (b) availability-driven (other metals for cobalt), (c) regulatory-driven (lighter for heavier materials in cars), and (d) functionality-driven (optical fibers for metal wire in communications). More general economy-wide examples include the substitution of coal, oil, and natural gas for wood as a fuel source, and the substitution of iron and steel, aluminum, cement, and plastic for wood as a construction material.
- Changes in the structure of final demand. The mix of goods and services produced and consumed by an economy change over time due to shifts among sectors, such as the rise of the service sector, or shifts within sectors, such as the increasing dominance of computers and other high-technology goods within the manufacturing sector. The general assumption is that the shift towards services and “high-tech” or “knowledge-intensive” products reduces the quantity of material required to produce a dollar’s worth of output. Changes in people’s preferences also could lead to an increased emphasis on the non-material aspects of consumer satisfaction.
- The saturation of bulk markets for basic materials. This line of reasoning holds that as an economy matures, there is less demand for new infrastructure such as bridges, roads, railways, steel factories and so on, reducing the need for steel, cement, and other basic materials.
- Government regulations that alter materials use. A prominent example in the U.S. is the regulation of lead additives in gasoline and other products that contributed to a sharp decline in the IU of lead.
There are other variables that determine the IU of a material, and the ones described above are not independent of each other. For example, technical changes often are accompanied by materials substitution, and it is difficult to separate the two effects in empirical analysis. However, most of the empirical work on dematerialization focuses on these driving forces.
- Cleveland, Cutler J. and Matthias Ruth, 1998. Indicators of Dematerialization and the Materials Intensity of Use. Industrial Ecology, 2:13-49.
- Considine, T. J., 1991. Economic and technological determinants of the material intensity of use. Land Economics, 67:99-115.
- Nakicenovic, N., 1990. Dynamics of Change and Long Waves. In: Vasko, T., Ayres, R. and Fontvieille, L. (Editor), Life Cycles and Long Waves. Springer-Verlag, Berlin, pp. 147-192. ISBN: 0387524738
- Wernick, I. K., Herman, R., Govind, S. and Ausubel, J. H., 1996. Materialization and dematerialization: measures and trends. Daedalus, 125:171-198.