SM5005 Chap.2 Process LCA and MRIO Perspectives
Process LCA and MRIO Perspectives
Two models expose different parts of the supply chain
Process life cycle assessment follows physical processes chosen by the analyst. Its strength is specificity: materials, energy technologies and production stages can be represented in units close to the engineering system. Its weakness is truncation.
Every investigation needs a stopping rule, and distant services or capital inputs can disappear at that edge.
Multiregional input-output modelling begins with the monetary transactions that connect sectors and regions. Because the accounts cover the economy, upstream requirements remain connected even when they are distant from the focal purchase. The cost of that coverage is aggregation.
A sector factor averages dissimilar producers and products, so it cannot automatically describe a named supplier or technology.
Choose by the decision and the dominant error
The useful comparison asks which mismatch threatens the decision. If a material substitution or production technology is central, product-level process data may be essential.
If the question concerns a large purchasing portfolio with thousands of lines, economy-wide coverage may be more valuable. Boundary completeness and specificity pull in different directions.
Neither method removes the need to state geography, time, price basis and uncertainty.
Hybridization is a replacement operation
A hybrid design keeps broad input-output coverage and replaces selected aggregate components with process-specific information. The analyst must identify the component already represented in the sector estimate and remove or adjust it before inserting the detailed inventory.
Otherwise the method adds detail and double counting at the same time. A hybrid is strongest when the replacement targets a material component whose aggregate representation is known to be weak.
What this chapter covers
- 01
Process inventories and physical flows
- 02
Truncation at a chosen process boundary
- 03
Economy-wide MRIO coverage
- 04
Sector aggregation error
- 05
Method choice by decision need
- 06
Hybrid replacement without overlap
Worked example · free
Selecting a method for two carbon questions
- 2Choose and justify the procurement method.
- 2State its dominant limitation.
- 2Choose and justify the technology method.
- 2State its dominant limitation.
Key terms
- Process Inventory
- A list of physical inputs, outputs and emissions for specified processes.
- Truncation Error
- Missing upstream activity caused by ending a process chain at a chosen boundary.
- Aggregation Error
- Mismatch caused by applying a sector average to a more specific product or producer.
- Economy-Wide Coverage
- Representation of linked transactions across the sectors in the accounting system.
- Hybridization
- Combining broad coverage with selected specific data after addressing overlap.
Process LCA and MRIO Perspectives FAQ
Is MRIO always more complete than process LCA?
It is structurally broad because the economic accounts connect sectors across upstream rounds, but completeness still depends on the model's regions, sectors, environmental extensions and treatment of imports. Broad coverage does not mean fine product detail or perfect source data.
Why not use only process data whenever they exist?
Availability does not guarantee consistent boundaries or representative data. Building process inventories for a large purchasing portfolio can also be infeasible. The method should match the decision, and detailed data should be reserved for components where specificity can change the conclusion.
What makes a hybrid estimate credible?
It identifies the aggregate component being replaced, explains why the specific data are better for the decision, removes the overlap, aligns units and years, and reports the changed boundary. Simply adding a process estimate to a sector estimate is not enough.
Assessment move
Build a two-column comparison from a single decision problem. For every claimed advantage, write the associated failure mode. Use one procurement portfolio and one named product comparison so the role of scale becomes visible. Mark the process stages a bottom-up inventory would follow and the services or capital inputs its stopping rule could omit.
On the MRIO side, identify the sector average, regional structure and product differences that aggregation would hide. State which error, truncation or aggregation, is more capable of changing each decision. Then sketch a hybrid that replaces one material aggregate component and mark exactly where overlap would otherwise occur.
Write an equivalence table for the baseline component and its detailed replacement, covering quantity, geography, period and life-cycle stages. Recalculate a small hypothetical baseline after subtracting the aggregate contribution and adding the process result. Explain why a detailed number with a narrower boundary may lower the result without improving it.
End with a method recommendation that contains both the strength being used and the limitation that needs a supplement. Repeat the recommendation after changing the decision from broad screening to supplier selection. If the method does not change when the information need changes, inspect whether you are choosing by familiarity rather than by the dominant source of error.
Support the recommendation with one boundary diagram and one sentence about data feasibility.
