In an attributional LCA we can determine some of the inputs whether they are from recycled or use the material and minimise their impact upfront. How would that be different if we use consequential LCA and assign displacement credit? Which method is more robust and more reliable for decision makers who lacks the knowledge for such details. I would appreciate hearing different views.
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Consequential LCA models the activities that change as a consequence of the demand for the input.
So, if your demand for recycled input leads to an increase in recycling, and a reduction in the amount of material going to final waste disposal, then your consequential inventory will include the increased recycling and the decreased final waste treatment.
If your demand for recycled input does not increase recycling (very often the case in well-developed recycling markets where all the material that can be recycled is already recycled and substituting virgin material) then your increased input of recycled material simply means that someone else can no longer purchase this recycled material and will have to use virgin material instead. So, in this situation, the net effect of your demand for recycled material is an increase in the equivalent amount of virgin production. So your consequential inventory will include this increase in virgin production and no change in recycling.
In attributional LCA you will typically include the recycling activity also in the second situation, even though there is no real world change in recycling. Similarly, attributional LCA will typically give too little credit for demanding recycled input in the first situation, even though the demand is fully determining the increase in real world recycling.
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Dear Dr. Ebotalib,
Adding to the response from Bo, Iād say that the difference between attributional and consequential modelling of recycling can be small in many cases. This requires that the attributional approach is designed to mirror the consequences of recycling.
A consequential LCA aims, as Bo writes, to model the consequences of the recycling.These include the impacts of the recycling and the credits from avoided waste disposal and primary production.
The cut-off approach is the most typical attributional approach to model recycling. This approach means that scrap material enters the product system without environmental impacts. Only the recycling process, or part thereof, is included in the product system. This will make the study robust, but the results will not reflect the consequences of your decisions.
However, a broader attributional perspective is possible, if attributional LCA is defined by its aim to identify what part of existing impacts should be assigned to the product you study. These impacts can include parts of the impacts of the primary production and final waste disposal of the material in the product. The allocation problem then includes the impacts of the actual primary production, recycling, and final disposal of this material.
In this broader attributional perspective, allocation factors can be chosen based on the foreseeable consequences of supplying or using recyclable scrap material. The attributional model will then give the same results as the consequential model, if the impacts of the actual primary production and final waste disposal are the same as the impacts of the avoided primary production and waste disposal.
However,in some cases the actual primary production and the avoided primary production are very different. This happens, for example, when recycled plastics substitutes wood. The attributional model will then include the actual primary production of the plastics, but the consequential LCA will include the avoided primary production of wood. In such cases, the attributional results will not reflects the foreseeable connsequences of recycling.