Why is CO2-non fossil not accounted for in the IPCC 2021 - Biogenic category

Question

I am wondering why does the "ecoInvent - IPCC 2021 climate change: biogenic - global warming potential" impact category does not account for CO2 - non fossil. 

Is there a way we can include CO2-non fossil in the "biogenic" results? 

Thank you very much.  

Answer 1

The "standard" and recommended approach from IPCC 2021 has net zero impacts of biogenic CO2 uptake and emission. It is a somewhat safe approach where one can assume that any biogenic carbon ends up in the atmosphere anyway at one point, so the net impact from uptake and emission is zero. This results in a characterisation factor of zero for "carbon dioxide, non-fossil" and for "carbon dioxide, in air", which is excluded from the characterisation factors and not shown in the impact category (we usually exclude characterisation factors that are zero). Maybe, at least for CO2, we could include the zero values into the characterisation factor tables to highlight there that these values are zero on purpose and not missing.

You are mentioning the ecoinvent implementation of IPCC 2021, which is only compatible with the ecoinvent database and where the biogenic carbon dioxide is set to zero correctly. You can even find the ecoinvent implementation (mapping) here:

https://github.com/ecoinvent/lcia/blob/master/3.10/methods_mapped/IPCC%202021_mapped_3.10.csv

You can include biogenic carbon by adding all elementary flows "Carbon dioxide, non-fossil" with +1, "Carbon dioxide, in air" with -1, "Carbon dioxide, non-fossil, resource correction" with -1 and changing all "Methane, non-fossil" from 27.0 to 29.8, which is similar to the EN15804 based on EF 3.1 and using IPCC 2021 for climate change categories.

But be aware that when the full life cycle is modelled and there is no significant carbon sink that lasts for several thousand years there should be (theoretically) no difference between tracking biogenic CO2 uptake/emissions (-1/+1) or putting it to net zero (0/0). But the risk is that explicitly tracking biogenic carbon uptake and emission can lead to unjustified claims of carbon credits or low carbon footprints due to the advantageous carbon uptakes in incomplete cradle-to-gate LCAs with no subsequent modelled release back into the atmosphere.

Comments

Dear Reed,

There is no difference if the full life cycle is modeled. You take an EoL treatment process of biowaste as an example. In the 0/0 approach, there is no emission counted for biogenic carbon at the end of life and there is no biogenic carbon accounted at the raw materials life cycle stage where the biomass is created by biogenic carbon uptake. Also in the -1/+1 approach the overall result should be zero, since you have an uptake counted as -1 and later an EoL emission of +1, which results in zero.

If you have to take 0/0 (usually all standard LCAs that are not EPDs) or -1/+1 (all EPDs according to EN15804 and all PCFs according to ISO14067) depends on your study and your standards to follow. IPCC 2021 is only giving the factors, but if biogenic carbon is explicitly accounted with uptake and emission (-1/+1) or if biogenic carbon is not accounted (because every biogenic carbon uptake will be emitted anyway back to the atmosphere resulting in zero overall impact) depends on the standard, on the goal and scope, on the study.

I would assume that TRACI 2.1 (but I have not double-checked it) uses the 0/0 approach, because the method goes back to 2012 where every LCIA method was using the 0/0 approach. Even old EPDs based on EN15804+A1 were based on the 0/0 approach from the CML method and only the newer ones based on EN15804+A2 use the -1/+1 approach.

As I wrote before, if you are free to chose the approach, the 0/0 is the "standard" LCA one and it is the safer approach, because you will not get any accounting inconsistencies from biogenic carbon imbalances in your product system or any accounting inconsistencies from mass distortions of biogenic carbon due to allocation in the background database.

Best wishes,
Conrad