All LCA research faces common challenges when defining the scope of the life cycle to be measured, what functional unit to use, how to deal with changes over time, and problems associated with allocation of shared inputs and outputs. However, the agriculture stage presents unique complexities for LCA, as defining the system boundaries is particularly difficult.
Source: FCRN and Dr Elin Röös.
For example, how should the emissions from deforestation of an area be allocated to the products that are grown on this land when arguably all agricultural production contributes to deforestation: even production on existing agricultural land, by preventing another crop being grown, could be seen as being indirectly responsible for ‘driving’ that production onto forest land?
- There may be multiple food and non food drivers of deforestation (e.g. both cattle ranching and logging)?
- Additionally, direct emissions are usually not easily measured; consider for example the difference between measuring the emissions from a factory chimney and measuring the emissions from hectares of agricultural land. Therefore, emissions usually have to be modelled rather than measured, a step which is associated with great uncertainties. Furthermore, emissions from agriculture vary widely depending on geographical location, production method, temperature, soil and rainfall patterns, and more. Generic data are therefore often used, so reducing the accuracy of the findings. To add to the complexity, soils can act as greenhouse gas sources (emissions) or sinks (absorbing emissions) and both land-use and agricultural practices can change over time.
In addition, quantifying emissions from animals (and their manure) is also difficult because of the large number of variables involved, including breed differences, quantifying methane emissions from enteric fermentation, different feeds and production systems, different impacts of different manure treatments, etc.
However, the scope of an LCA usually encompasses far more than the agricultural stages of the food supply chain, and all stages can present difficulties with respect to scope. For example, food products are processed, often refrigerated, transported and stored for different times. Food can be prepared in different ways (e.g. a carrot can eaten raw, microwaved, boiled or roasted). The impacts associated with all these stages need to be understood and quantified.
As such, there is a considerable degree of uncertainty when measuring the environmental impacts of food.