Biogenic Carbon — What it is and how is it accounted

With the attention on carbon emissions caused by anthropogenic activity, one often forgets that carbon is a naturally occurring element of the Earth’s atmosphere with a natural cycle of its own. Biogenic carbon is an integral part of this natural carbon cycle and is referred to the carbon that is stored in, sequestered, and released by organic matter.

Carbon is added to plants and trees, throughout their lifetime due to the process of photosynthesis and the stored carbon is released as a result of either decomposition or combustion at the end of the plant’s life cycle. These emissions that occur as a result of decomposition or combustion of biomass are known as biogenic carbon emissions.

On the other hand, non-biogenic carbon is the carbon that is not derived from biomass and most commonly is referred to as carbon that is stored in fossil fuels. Combustion of fossil fuels amount to significant carbon emissions and those that take a long time to be reabsorbed.

Two different approaches can be identified for assessment of biogenic carbon in Life Cycle Analysis (LCA) conducted for buildings. The first one which is referred to as the “carbon neutral approach” or the “0/0 approach” is built on the hypothesis that the amount of carbon uptake during the growth of biomass is equivalent to the amount of carbon released at the end of life of the bio-based material. This leads to a balance in the amount of carbon uptake and release.

The other approach which is referred to as the “-1/+1 approach” takes into account all biogenic carbon flows of a building through its entire life cycle. When a bio-based building material is used, the stored biogenic carbon in the biomass enters the building system and is reported as negative emission. A positive emission is accounted at the end of the life of the building when either the biogenic carbon is released back into the atmosphere or further transferred to another building system. In these two scenarios, a positive emission is accounted for in Life cycle stage C. The advantage of the -1/+1 approach over the 0/0 approach is that it provides an overview of biogenic carbon flows but there could be misleading results with only the impact of the material life cycle stages of production and construction with uptake of biogenic carbon is taken into account and not release at the end-of-life cycle.

Another school of thought is that the LCA approaches do not take into account the “timing of carbon emissions” and impact of rotation periods of biomass growth. For example, trees are considered to have longer rotation periods and cannot be considered as carbon neutral in a short time span whereas materials such as straw are fast growing and hence have a shorter rotation period and can be more effective towards carbon removal from the atmosphere.

In EN 15804 +A1, it was feasible to account for biogenic carbon stored in a product only if it was sourced from a sustainably run forest, calculating the cradle to gate impact, and then summing them to signify their release at the end-of-life stage. The revised EN 15804 + A2 EPD standard states that the biogenic carbon mass of a product and for the packaging has to be declared.

Previously, reported as a single number, GWP — Global Warming Potential would not differentiate between biogenic, fossil, land use classification which is now divided into four different categories in the revised version. These include:

· GWP total (total of subgroups)

· GWP fossil

· GWP biogenic

· GWP luluc (land use and changes)

On our platform, the biogenic carbon stored in a product is accounted and represented as an additional information to expand on the environmental impact data of the product. Biogenic carbon is accounted for the whole life cycle stages of a product including production (A1-A3), on-site installation (A5), use and maintenance (B1-B5), and end-of-life stage (C1, C3, C4). Stages A4 ( Transport to site) and C2 ( Transport — end of life) are excluded from calculations because of a lack of accuracy of data but will be added as we expand the platform to take into account the construction site location.