37
describe intermediate demand. Technological detail is high in both model families, and in IAMs, industrial assets are often modeled as discrete units to simulate individual plants. Technological change is exogenous in IE models but
endogenous in some IAMs. We see three ways in which IE principles can
improve the modeling of production processes in IAMs: (1) mass balance consistency between industrial input and output, inclusion of waste generation and
recycling; (2) consideration of multi-output processes and industrial symbiosis,
that is, joint production of commodities and by-products within and across
industrial sectors; (3) separate description of primary and secondary material
production. Point (4) is already part of several IAMs, but the way scrap supply
is modeled differs substantially across different IAMs, and not all approaches
are meaningful from an IE perspective.
(2) Markets and products : In IE models and IAMs, markets balance supply and
demand. It is common in IE to distinguish between markets for primary products and waste and to require the models to clear both markets at the same time.
Introduction of waste markets into IAMs and the development of mechanisms
for how they are cleared would allow for realistic modeling of waste treatment
and recycling activities. Detailed descriptions of waste handling, recycling, and
substitution of secondary for primary materials are essential in understanding
how a transition to a more circular economy could happen; they should therefore be an integral part of future prospective models. More details regarding the
quality of materials, for example, by considering different alloys, will be necessary to build scenarios for the use of secondary materials in different products.
(3) The fi nal use phase comprises in-use stocks such as products used by households, public buildings and infrastructure, and industrial assets. Both prospective IE models and IAMs use age-cohort-based dynamic models to represent
in-use stocks. The age cohort technology composition of industrial assets, vehicles, or buildings determines the overall intermediate energy and material
requirements to produce industrial output, drive vehicles, or heat buildings, and
modeling this relation is the traditional strength of IAMs. In-use stocks, however, also represent material stocks or “urban mines.” Modeling the material
layer of in-use stocks along with their economic value and technical coeffi -
cients allows us to obtain a comprehensive picture of stocks and to connect the
future extent of waste recovery and recycling to the physical turnover of industrial assets and other in-use stocks. The principles for this multilayer modeling
of stocks are presented elsewhere (Pauliuk et al. 2015 ), and to implement them
into IAMs, one needs to amend the description of in-use stocks by adding the
material composition layer.
IAMs can also be extended regarding the interaction of SEM with environment
and society . Due to their focus on climate change, IAMs generally focus on greenhouse gas emissions , but other types of emissions, such as particulate matter or
heavy metals and other toxic substances, can be readily included (Gibon et al.
2015 ). IAMs contain detailed descriptions of biotic resources but should be extended
to better refl ect the depletion of mineral resources, especially metal ores. More
2 Prospective Models of Society’s Future Metabolism: What Industrial Ecology Has…
describe intermediate demand. Technological detail is high in both model families, and in IAMs, industrial assets are often modeled as discrete units to simulate individual plants. Technological change is exogenous in IE models but
endogenous in some IAMs. We see three ways in which IE principles can
improve the modeling of production processes in IAMs: (1) mass balance consistency between industrial input and output, inclusion of waste generation and
recycling; (2) consideration of multi-output processes and industrial symbiosis,
that is, joint production of commodities and by-products within and across
industrial sectors; (3) separate description of primary and secondary material
production. Point (4) is already part of several IAMs, but the way scrap supply
is modeled differs substantially across different IAMs, and not all approaches
are meaningful from an IE perspective.
(2) Markets and products : In IE models and IAMs, markets balance supply and
demand. It is common in IE to distinguish between markets for primary products and waste and to require the models to clear both markets at the same time.
Introduction of waste markets into IAMs and the development of mechanisms
for how they are cleared would allow for realistic modeling of waste treatment
and recycling activities. Detailed descriptions of waste handling, recycling, and
substitution of secondary for primary materials are essential in understanding
how a transition to a more circular economy could happen; they should therefore be an integral part of future prospective models. More details regarding the
quality of materials, for example, by considering different alloys, will be necessary to build scenarios for the use of secondary materials in different products.
(3) The fi nal use phase comprises in-use stocks such as products used by households, public buildings and infrastructure, and industrial assets. Both prospective IE models and IAMs use age-cohort-based dynamic models to represent
in-use stocks. The age cohort technology composition of industrial assets, vehicles, or buildings determines the overall intermediate energy and material
requirements to produce industrial output, drive vehicles, or heat buildings, and
modeling this relation is the traditional strength of IAMs. In-use stocks, however, also represent material stocks or “urban mines.” Modeling the material
layer of in-use stocks along with their economic value and technical coeffi -
cients allows us to obtain a comprehensive picture of stocks and to connect the
future extent of waste recovery and recycling to the physical turnover of industrial assets and other in-use stocks. The principles for this multilayer modeling
of stocks are presented elsewhere (Pauliuk et al. 2015 ), and to implement them
into IAMs, one needs to amend the description of in-use stocks by adding the
material composition layer.
IAMs can also be extended regarding the interaction of SEM with environment
and society . Due to their focus on climate change, IAMs generally focus on greenhouse gas emissions , but other types of emissions, such as particulate matter or
heavy metals and other toxic substances, can be readily included (Gibon et al.
2015 ). IAMs contain detailed descriptions of biotic resources but should be extended
to better refl ect the depletion of mineral resources, especially metal ores. More
2 Prospective Models of Society’s Future Metabolism: What Industrial Ecology Has…