The ISO 14040 standards for consequential LCA

The ISO 14040 series of standards on Life Cycle Assessment provide the basic requirements for consequential LCA, even if they do not make a clear distinction between “attributional” and “consequential” modelling.

The original ISO 14040 series of standards were published in 1997, which was before the distinction between “attributional” and “consequential” models had become clear. The first to make this distinction clear was Tillman (in her 1998 key-note lecture “Significance of decision making for LCA methodology” to the 8th Annual Meeting of SETAC-Europe in Bordeaux). The term “attributional” was not coined until 2001 (on an International Workshop on Electricity Data for Life Cycle Inventories in Cincinnati, 2001.10.23-25) and was not defined before 2011 (in the UNEP/SETAC Shonan Guideline).

The revision of the ISO 14040 series in 2006 did also not introduce the distinction between “attributional” and “consequential” models, since it was decided to limit this revision to a simple re-writing of the original standards, separating the framework (ISO 14040) from the requirements (ISO 14044) without any intention of changing the actual text and prescriptions of the original standard series.

However, the ISO 14040 series is part of the overall ISO 14000 series on Environmental Management Systems (EMS), which has a commitment to continual improvement as a basic requirement for the EMS policy statement. It is therefore obvious that also the ISO 14040 series is concerned with improvements rather than measuring the status-quo. This is also clear from the introduction to ISO 14040:2006 where all the listed applications of LCA are about improvements:

“LCA can assist in:

  • identifying opportunities to improve the environmental performance of products at various points in their life cycle,
  • informing decision-makers (…), e.g. for the purpose of strategic planning, priority setting, product or process design or redesign,
  • the selection of relevant indicators of environmental performance,
  • marketing (e.g. implementing an ecolabelling scheme, making an environmental claim, or producing an environmental product declaration).”

Furthermore, in the “Principles for LCA” provided in ISO 14040:2006 (clause 4.1.8), the principle of “Priority of scientific approach” is described in this way:

“Decisions within an LCA are preferably based on natural science. If this is not possible, other scientific approaches (e.g. from social and economic sciences) may be used or international conventions may be referred to. If neither a scientific basis exists nor a justification based on other scientific approaches or international conventions is possible, then, as appropriate, decisions may be based on value choices.”

It should be clear from this text that normative value choices, like those needed for allocation in attributional LCA, should be the last resort, and that in general scientific principles like mass balances (which cannot generally be obtained in attributional models) have first priority.

The so-called allocation hierarchy in ISO 14044 (Clause begins in this way:

“The study shall identify the processes shared with other product systems and deal with them according to the stepwise procedure:

a) Step 1: Wherever possible, allocation should be avoided by

  • dividing the unit process to be allocated into two or more sub-processes and collecting the input and output data related to these sub-processes, or
  • expanding the product system to include the additional functions related to the co-products

b) Step 2: Where allocation cannot be avoided, (…)”

For consequential LCA, it is sufficient to read step 1, since allocation can always be avoided by the two procedures described in Step 1, as is demonstrated by the theory and examples on this web-site. The reason for the remaining options to be included in ISO 14044 (originally ISO 14041) was that at the time of writing (1996), it was not completely clear that allocation could always be avoided, and the remaining steps were therefore included as a kind of “safety valve”.

The allocation clause furthermore contains this paragraph:

“The inventory is based on material balances between input and output. Allocation procedures should therefore approximate as much as possible such fundamental input-output relationships and characteristics.”

which is a clear hint to consequential modeling, which is the only way to maintain mass (and other) balances intact during inventory calculation.

The ISO 14040 allocation clause furthermore ends with a reference to ISO 14049, which describes the procedure for system expansion in this way (emphasis added):

“The supplementary processes to be added to the systems must be those that would actually be involved when switching between the analysed systems. To identify this, it is necessary to know:

  • whether the production volume of the studied product systems fluctuate in time (in which case different sub-markets with their technologies may be relevant), or the production volume is constant (in which case the base-load marginal is applicable),
  • (…) whether (…) the inputs are delivered through an open market, in which case it is also necessary to know:
  • whether any of the processes or technologies supplying the market are constrained (in which case they are not applicable, since their output will not change in spite of changes in demand),
  • which of the unconstrained suppliers/technologies has the highest or lowest production costs and consequently is the marginal supplier/ technology when the demand for the supplementary product is generally decreasing or increasing, respectively.” (ISO 14049 – Clause 6.4)

Considering that this was written in 1996, it is a surprisingly precise description of why and how to identify the marginal suppliers (compare to our current description).

In conclusion, the ISO 14040 series are supporting a consequential interpretation, even when this is not as explicit as it could be done if the standards were to be re-written today.

These topics are also explained in this video (go to Youtube video)

Further reading
ISO (2006a). ISO 14040 International Standard. In: Environmental Management – Life Cycle Assessment – Principles and Framework. International Organisation for Standardization, Geneva, Switzerland.ISO, 2006b.

ISO (2006b) ISO 14044 International Standard. In: Environmental Management – Life Cycle Assessment – Requirements and Guidelines. International Organisation for Standardisation, Geneva, Switzerland. 

Weidema B P (2014). Has ISO 14040/44 failed its role as a standard for LCA? Journal of Industrial Ecology 18(3):324‑326

How to cite this: 
Consequential-LCA (2015). The ISO 14040 standards for consequential LCA. Last updated: 2015-10-27.