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Table 1 The relevance of materials for GHG emissions, end use based system boundaries, based on actual
emissions according to IPCC accounting guidelines
CO2 Non-CO2 GHG Total Fraction
[Mt CO2 equiv.pa] [Mt CO2 equiv.pa] [Mt CO2 equiv.pa] [%]
Metals 244 11 255 26
Synthetic organic
materials
167 53 220 22
Natural organic materials 93 130 223 22
Inorganic materials 49 60 109 11
Ceramic materials 191 - 191 19
Total 744 254 998 100
The flows of energy and materials through the economy can be analysed in a systems approach. “A system is a
structured assemblage of elements and subsystems, which interact through interfaces. The interaction occurs
between system elements and between the system and its environment. The element and their interactions constitute
a total system, which satisfies functional, operational and physical characteristics, as defined by the user
and customer needs and requirements, over a defined total system life cycle of the system in existence, including
the life cycle of bringing the system into being” [3]
The system elements in the economy are called processes. They are defined by their energy and material inputs
and outputs, by their emissions and by their costs. Examples are a blast furnace (input coal and coke, output
liquid iron), a car manufacturing plant (input steel sheet, other materials and energy, output cars), landfill sites
(input waste materials). The interfaces between the processes are called flows. They include energy flows and
material flows. The function of the system is to satisfy a demand from the final users (e.g. a demand for housing,
transportation, lighting and packaging). Constraints are for example added for the availability of resources,
for the social acceptance of processes (like nuclear power plants or public transportation) and for the environmental
impact of the system (like GHG emissions).
How long is the life cycle of the system ? The definition encompasses all steps from the early system conception
to its final abolishment. For the economy as a whole, it is difficult to set these boundaries. From a systems engineering
point of view for GHG emission reduction, it is more relevant to analyze the system dynamics: how
much time is required to achieve significant changes in the system configuration in order to change its environmental
impact.
The dynamics of the energy and materials system are defined by the rate of technological change, the turn-over
rate of production processes, and the product life. The rate of technological change is often overestimated.
Technological breakthroughs require decades, even if the development is successful. Many key processes in the
energy and materials system show little technological change over the last century. Examples are blast furnaces,
Hall-Heroult smelters for aluminium production, pulp mills, ignition engines for e.g. passenger cars.
Gradual efficiency improvements have occured, but the technical basic principle has not changed. Development
of alternatives was not succesful because of technological problems or because of worse process economics.
Even if technology development is successful, the actual introduction is hampered by the slow diffusion processes
for new technology. Literature data suggest the the time required for a new process to unfold from 10% to
90% of the market share ranges from one decade to several centuries, depending on the pervasiveness of the
technology and the interaction with existing practices and technologies [4]. Diffusion of new technologies is
also hampered by the life span of existing capital equipment. The life span of industrial equipment ranges from
1 to 5 decades. The life span of infrastructure ranges from 5 to 10 decades.
Data for materials production suggest similar slow system dynamics. Figure 3 shows the materials production
trends for a number of “old” materials (steel, cement) and “new” materials (polyethylene, aluminium). It is interesting
to see the strong growth of paper production, despite the fact that this is the material with the longest