33
not only on the product system of the investigated product but also on the product
systems of other products and, in particular, the production volumes of and demand
for those products. This dependence on other product systems is most clearly visible
when scientists, under the heading of “consequential LCA,” address the question of
what happens to constrained resources when a product is not produced. In the opinion of some, the consequential life-cycle emissions of a bicycle should include
those of combusting the petrol that it does not use because somebody else will
combust that petrol as a response of the market to the bicycle not using that petrol
(Plevin et al. 2014a , b ). One of us (Hertwich 2014 ) has questioned whether it makes
sense to say that the petrol not combusted by the bicycle is part of the product system “bicycle” only because one could have used a car instead. It is also problematic
to say that riding the bicycle to work causes petrol combustion somewhere else in
the economy due to price elasticity. The petrol combustion is rather the consequence
of somebody else’s decision somewhere else in the economy.
It is of course a legitimate research questions to ask, e.g., what is the effect of the
massive and intended expansion of cycling in Copenhagen on GHG emissions ? The
question, however, remains ill-defi ned until one juxtaposes the observed or planned
expansion of cycling to some counterfactual possible scenario of increased car or
bus transport. In addition, one needs to defi ne the scope and functioning of the system investigated, including the causal mechanisms to be addressed. Mechanisms
may or may not include the fuel market response to the petrol demand in the counterfactual scenario, the effect of the inspiration Copenhagen now provides to town
planners all over the world and the effect of increased life expectancy of the cyclists
on food demand and future economic development. Then one has two scenarios to
compare, and one may colloquially argue the difference between the scenarios that
indicates the effect of Copenhagen’s cycling policy and the enthusiastic popular
response it has received. Such causality is an imputed, assumed causality; the
assumptions are made in the setup of the systems model and the defi nition of the
scenarios and the imputation in the interpretation of the scenario results as showing
the difference. Other system models and scenario assumptions may be equally reasonable; the true consequences are unmeasurable because we do not have a second
Earth to run an experiment on.
The early developers of systems expansion as a way of addressing allocation issues
fully understood that system expansion involved assumptions about other product
systems and that results should be interpreted with these assumptions in mind.
We expand our above argument regarding the predictive capacity of prospective
models for indeterminate systems and assert that the hypothetical CLCA approach
as described by Plevin et al. ( 2014a ) faces a dilemma: The capability of the hypothetical CLCA model to reliably predict the future outcome is the better the smaller
the changes to the system and the shorter the time horizon, because fewer human
actors, who are the major source of indeterminacy, are involved if changes are small
and local and the inertia represented by existing stocks is larger in the near future.
Modeling on the small scale with short time horizons is the opposite of what is
needed for studying strategies for a socio-metabolic transition, however, and for
large-scale and long-term changes, prediction remains an illusion. Therefore, we
2 Prospective Models of Society’s Future Metabolism: What Industrial Ecology Has…
not only on the product system of the investigated product but also on the product
systems of other products and, in particular, the production volumes of and demand
for those products. This dependence on other product systems is most clearly visible
when scientists, under the heading of “consequential LCA,” address the question of
what happens to constrained resources when a product is not produced. In the opinion of some, the consequential life-cycle emissions of a bicycle should include
those of combusting the petrol that it does not use because somebody else will
combust that petrol as a response of the market to the bicycle not using that petrol
(Plevin et al. 2014a , b ). One of us (Hertwich 2014 ) has questioned whether it makes
sense to say that the petrol not combusted by the bicycle is part of the product system “bicycle” only because one could have used a car instead. It is also problematic
to say that riding the bicycle to work causes petrol combustion somewhere else in
the economy due to price elasticity. The petrol combustion is rather the consequence
of somebody else’s decision somewhere else in the economy.
It is of course a legitimate research questions to ask, e.g., what is the effect of the
massive and intended expansion of cycling in Copenhagen on GHG emissions ? The
question, however, remains ill-defi ned until one juxtaposes the observed or planned
expansion of cycling to some counterfactual possible scenario of increased car or
bus transport. In addition, one needs to defi ne the scope and functioning of the system investigated, including the causal mechanisms to be addressed. Mechanisms
may or may not include the fuel market response to the petrol demand in the counterfactual scenario, the effect of the inspiration Copenhagen now provides to town
planners all over the world and the effect of increased life expectancy of the cyclists
on food demand and future economic development. Then one has two scenarios to
compare, and one may colloquially argue the difference between the scenarios that
indicates the effect of Copenhagen’s cycling policy and the enthusiastic popular
response it has received. Such causality is an imputed, assumed causality; the
assumptions are made in the setup of the systems model and the defi nition of the
scenarios and the imputation in the interpretation of the scenario results as showing
the difference. Other system models and scenario assumptions may be equally reasonable; the true consequences are unmeasurable because we do not have a second
Earth to run an experiment on.
The early developers of systems expansion as a way of addressing allocation issues
fully understood that system expansion involved assumptions about other product
systems and that results should be interpreted with these assumptions in mind.
We expand our above argument regarding the predictive capacity of prospective
models for indeterminate systems and assert that the hypothetical CLCA approach
as described by Plevin et al. ( 2014a ) faces a dilemma: The capability of the hypothetical CLCA model to reliably predict the future outcome is the better the smaller
the changes to the system and the shorter the time horizon, because fewer human
actors, who are the major source of indeterminacy, are involved if changes are small
and local and the inertia represented by existing stocks is larger in the near future.
Modeling on the small scale with short time horizons is the opposite of what is
needed for studying strategies for a socio-metabolic transition, however, and for
large-scale and long-term changes, prediction remains an illusion. Therefore, we
2 Prospective Models of Society’s Future Metabolism: What Industrial Ecology Has…