In-use product stocks link manufactured capital to natural capital

Abstract

In-use stock of a product is the amount of the product in active use. In-use product stocks provide various functions or services on which we rely in our daily work and lives, and the concept of in-use product stock for industrial ecologists is similar to the concept of net manufactured capital stock for economists. This study estimates historical physical in-use stocks of 91 products and 9 product groups and uses monetary data on net capital stocks of 56 products to either approximate or compare with in-use stocks of the corresponding products in the United States. Findings include the following: (i) The development of new products and the buildup of their in-use stocks result in the increase in variety of in-use product stocks and of manufactured capital; (ii) substitution among products providing similar or identical functions reflects the improvement in quality of in-use product stocks and of manufactured capital; and (iii) the historical evolution of stocks of the 156 products or product groups in absolute, per capita, or per-household terms shows that stocks of most products have reached or are approaching an upper limit. Because the buildup, renewal, renovation, maintenance, and operation of in-use product stocks drive the anthropogenic cycles of materials that are used to produce products and that originate from natural capital, the determination of in-use product stocks together with modeling of anthropogenic material cycles provides an analytic perspective on the material linkage between manufactured capital and natural capital.

Keywords: in-use stocks; industrial ecology; manufactured capital; sustainability.

Fig. 1.

In-use product stocks drive anthropogenic material cycles and provide functions or services demanded by modern human society. Fabri, fabrication; Manuf, manufacturing; Dis, discard, disposal, and dismantling; Recyl, recycling.

Fig. 2.

Examples of absolute (abs.), PC (per cap.), per adult, or PHH (per HH) in-use or net capital stocks (in constant 2000 US$) of products in the United States: locomotives (A); road vehicles (B); buildings (C); machinery (D); ranges and ovens (E); computer CPUs and mobile phones (F); TVs (G); storage devices (H); books (I); aluminum cans (J); electricity generation capacities (K); and electricity transmission lines (L). More figures and data sources are available in SI Appendix.

Fig. 3.

Waves of the historical evolution of in-use stocks for transportation infrastructures (A), transportation facilities (B), home appliances (C), and electronic products (D) in the United States. The thin lines in A, B, and D, as well as all lines in C show the empirical data; the bold, smooth lines in A, B, and D show results of the S-curve fitting.