Accounting of biogenic carbon in attributional LCA - including temporary storage
Climate change poses one of the largest challenges to mankind. It’s clear that significant mitigation efforts are needed in order to reach a sustainable development for our and future generations. One important strategy in climate mitigation is to convert fossil based industrial processes to those based on renewable sources. In order to make this transition possible, we will have to change to a more biobased economy. Furthermore, the energy required for the production of non-renewable materials such as steel and cement, should as much as possible be based on renewable resources in the future and will, therefore, potentially compete for the same renewable resource stock.
In each application, the best use of the renewable resources has to be evaluated. Life cycle assessment (LCA) is an analytic tool that can be used for such comparative purposes. In order to make the LCA results robust, the used methodologies and their features need to be strictly specified. If the LCA practitioner has too much freedom when applying the methodology, this may result in ambiguous results. This development is actually part of an ongoing market driven development where LCA based declarations for product are used as information modules, as defined by numerous international standards (ISO 14040, -44, -25 and e.g. ISO 21930). These resulting environmental product declarations (EPD) are supplied by the manufacturers, and then used by others in the supply chain, to for instance calculate the impact from construction projects.
The system perspective chosen for these EPD is a so called attributional LCA. An attributional LCA builds on a modular approach (Erlandsson et al 2015) and on the additivity principal (Tillman 2000). This approach is also described as the “100% rule”, where the sum of impacts from all attributional allocated product systems equals the global impact, ideally. The same system perceptive is e.g. used for national greenhouse gas inventories (IPCC 2006). An alternative system perspective, answering another question, is a so called consequential LCA. A consequential LCA is used to assess a marginal and often hypothetical change as compared to a reference case. The consequential LCA provides a complimentary result to the attributional LCA, describing “what happens if” a particular change is introduced. Attributional LCA methodology is more commonly used in the EPD context since it is more unequivocal. In this paper we have therefore chosen the attributional approach in order to achieve an applicable method for EPD.