Metal stocks in society

Source: UNEP, 2010. Metal stocks in society.

These attractive and simple Material Flow Analysis diagrams are from the scientific sythesis report of UNEP and the International Resource Panel.

Material flow analysis characterizes and quantifies flows of materials into, out of, and through a system of interest, equating flows at each reservoir within the system by conservation of mass. In this analysis, the choice of scale and level is critical (scale is “a spatial, temporal, quantitative, or analytic dimension used to measure or study a phenomenon” [Gibson et al., 2000], as with a ruler, level is a position along the scale.) The quantity of mass of a chosen material that exists within the system boundary of choice at a specific time is considered stock within the system. In terms of units of measurement, stock is a level variable (i. e., kg), while flow is a rate variable (i. e., kg per unit of time). In general, the metal stock in society is highest by far when material is in use (rather than in processing, fabrication, manufacturing, or waste management).