The ISO 14040 series on life cycle assessment provides the basic requirements for consequential LCA, even though they do not make a clear distinction between "attributional" and "consequential" models.
The original ISO 14040 standard series was published in 1997, before the distinction between "attributional" and "consequential" models became well defined. The first to make this distinction clear was Tillman (in his keynote address in 1998"Significance of decision making for LCA methodology" at the 8th annual SETAC-Europe meeting in Bordeaux). The term "attributional" was not coined until 2001 (at an international workshop on electricity data for life cycle inventories in Cincinnati, October 23-25, 2001) and was not defined until 2011 (in the UNEP/SETAC guidelines).
Even the revision of the ISO 14040 series in 2006 did not introduce the distinction between "attributional" and "consequential" models, as it was decided to limit this revision to a simple rewriting of the original standards, separating the framework (ISO 14040) from the requirements (ISO 14044) without any intention of changing the current text and prescriptions of the original standard series. However, the ISO 14040 series is part of the ISO 14000 series on environmental management systems (EMS), which requires a commitment to continuous improvement as a fundamental requirement.
The goals of an LCA are:
- Identify opportunities to improve the environmental performance of products at various points in their life cycle;
- Inform decision-makers (...), for example for strategic planning, defining priorities, product or process design or redesign;
- Select relevant environmental performance indicators;
- Marketing (e.g., implementing an eco-labeling system, making an environmental claim or producing a product environmental statement)."
Furthermore, in the "Principles for LCA" provided by the ISO 14040:2006 standard (section 4.1.8), the principle of "Priority of the scientific approach" is described as follows:
"Decisions within an LCA are preferably based on natural sciences. If this is not possible, other scientific approaches (e.g., those of social and economic sciences) can be used or international conventions can be referred to. If there is no scientific basis and no justification based on other scientific approaches or international conventions, then, depending on the case, decisions can be based on value choices".
It should be clear from this text that normative value choices, such as those required for allocation in attributional LCA, should be a last resort, and that in general scientific principles such as mass balances (which generally cannot be achieved in attributional models) have first priority.
The so-called allocation hierarchy in the ISO 14044 standard (section 4.3.4.2) begins as follows:
"The study shall identify shared processes with other product systems and treat them according to the following gradual procedure:
a) Phase 1: where possible, allocation should be avoided
- divide the process unit to be allocated into two or more sub-processes and collect the input and output data related to these sub-processes, or
- expand the product system to include additional functions related to co-products
b) Phase 2: where allocation cannot be avoided, (...)"
For a consequential LCA, it is sufficient to read phase 1, as allocation can always be avoided through the two procedures described, as demonstrated by theory and examples in upcoming lessons. The reason the remaining options were included in ISO 14044 (originally ISO 14041) was that at the time of drafting these articles (1996), it was not entirely clear that allocation could always be avoided, and the remaining phases were therefore included as a kind of "safety valve".
Paragraph 4.3.4.2 also contains this paragraph:
"The inventory is based on material balances between input and output. Allocation procedures should therefore come as close as possible to these input-output relationships and fundamental features".
This could be a hint at consequential modeling, which is the only way to keep mass balances (and others) intact during inventory calculation. The paragraph also ends with a reference to ISO 14049, which describes the procedure for expanding the system as follows:
"Additional processes to be added to the systems should be those that would actually be involved in the transition between the systems analyzed. To identify this, it is necessary to know:
- whether the production volume of the product systems studied fluctuates over time or the production volume is constant;
(...) if (...) inputs are delivered through an open market, in which case it is also necessary to know:
- if any of the processes or technologies supplying the market are tied (in which case they are not applicable, as their production will not change despite changes in demand),
- which of the untied suppliers/technologies has higher or lower production costs and consequently is the marginal supplier/technology when the demand for the additional product is generally respectively decreasing or increasing. (ISO 14049 - Section 6.4)
Considering that it was written in 1996, this is a surprisingly accurate description of how to identify marginal suppliers.
Sources:
- ISO (2006a). ISO 14040 International Standard. In: Environmental Management – Life Cycle Assessment – Principles and Framework.International Organisation for Standardization, Geneva, Switzerland.ISO, 2006b.http://www.iso.org/iso/catalogue_detail?csnumber=37456
- ISO (2006b) ISO 14044 International Standard. In: Environmental Management – Life Cycle Assessment – Requirements and Guidelines. International Organisation for Standardisation, Geneva, Switzerland. http://www.iso.org/iso/catalogue_detail?csnumber=38498
- Weidema B P (2014). Has ISO 14040/44 failed its role as a standard for LCA? Journal of Industrial Ecology 18(3):324‑326 http://lca-net.com/p/1273
Next lesson - The functional unit
