CO₂ balance: biogenic carbon and what companies need to consider

If you work with biogenic raw materials, you should take a close look: Depending on the accounting approach, the CO₂ assessment can vary greatly – and with it the validity of your information in marketing, product communication or reporting. In this article, you will learn what is important when it comes to biogenic carbon and how to choose a methodology that delivers consistent and comprehensible results.

Not all CO₂ is the same – and that makes all the difference to your carbon footprint 

In order to create a CO₂ balance or LCA (life cycle analysis) that is as meaningful and valid as possible, it is essential to differentiate between fossil and biogenic carbon. Depending on the application and the LCA methodology used, the carbon balance and therefore the PCF (Product Carbon Footprint) varies considerably.

When comparing different products in particular, it is easy to make misjudgements if different approaches are mixed up. This harbours risks –particularly with regard to marketing claims, for example in the context of the Green Claims Directive. A clean and consistent balance sheet is therefore not only crucial for your own analyses, but also for credible and legally compliant communication.

The main approaches to carbon accounting: 0/0 vs. +1/-1

There are two common methods for accounting for biogenic carbon: the 0/0 approach and the +1/-1 approach.

In the 0/0 approach, biogenic carbon is not taken into account, as it is assumed that released biogenic emissions will soon be absorbed again by renewable biomass – provided that land use remains constant and the carbon cycle remains closed. This means that CO₂ emissions from the combustion or decomposition of biogenic materials such as wood are not included in the global warming potential (GWP). The GWP describes the relative contribution of a greenhouse gas to global warming over a defined period (usually 100 years, GWP100) in relation to CO₂ as a reference gas and is the central parameter for calculating the carbon footprint of a product or company. Stored biogenic CO₂ is also not included in the calculation, so it is not accounted for either when it is absorbed or released. As a result, bio-based materials may perform worse than fossil-based products if the accounting framework does not cover the entire product life cycle. This is also shown in the simplified example in the following diagrams: Two fictitious products – one fossil-based, one bio-based – go through the same manufacturing process with identical CO₂ emissions. As the biogenic CO₂ is not accounted for according to the 0/0 approach, the two products do not differ from each other until the end of production. Both have caused 40 kg of CO₂ emissions up to the gate. Only at the end of the life cycle do they differ, as only the fossil carbon is taken into account. This accounting approach is used, for example, in the impact assessment methods according to ReCiPe2016 or PEF (Product Environmental Footprint).

This contrasts with the +1/-1 approach. In this case, the CO₂ absorbed by the biomass as it grows is recognised as -1, i.e. it is included in the balance with a negative credit, as the CO₂ is removed from the atmosphere. The carbon released is included in the balance with an emission factor of +1 as a positive emission value. This differentiated approach makes it possible to take into account the time lag between the release of CO₂ and its reabsorption by plants, as this can span many decades during which the biogenic carbon remains stored in the product. This is also shown by the fictitious example in the figures below. The CO₂ credit for the biogenic product makes it possible to recognise a clear difference to the fossil product immediately after production. This approach is therefore often used for processes where carbon sequestration does not occur immediately. These include wood products used for many years, land use changes with longer-term carbon sequestration or agricultural or forestry processes. This accounting approach is used, among other things, when preparing PCFs in accordance with ISO 14067 or environmental product declarations (EPDs)/LCAs in accordance with EN15804.

One advantage of the +1/-1 approach is when biogenic materials are subsequently combined or further processed with fossil components. In such cases, the biogenic carbon content does not have to be passed along the entire supply chain and rebalanced – it is sufficient to record the net emissions from the overall processing as +1 at the end. However, there is a risk that downstream partners will misinterpret the balance values, especially if they continue to work with the 0/0 approach. This can lead to double counting or underestimation, which significantly worsens the balance of the product. To avoid such misunderstandings, it can help to state a value with and without biogenic carbon so that it is clearly documented which accounting approach is used.

Why you should also keep an eye on biogenic methane

Biogenic methane (CH₄) is released when biogenic materials are fermented, composted or converted in other biological processes, as is the case in biogas plants, for example. Although the carbon it contains originally comes from the atmosphere here too, it is not released as CO₂, but is emitted into the ambient air in the form of CH₄. The problem: as a greenhouse gas, methane has a significantly higher global warming potential than CO₂ and has a much more damaging effect on the climate over a period of 100 years. After some time in the atmosphere, the methane oxidises back to CO₂, which is also included in the assessment. This is particularly relevant for biogenic CH₄, as the question arises here: does the original methane count – or the CO₂ that it later becomes? The assessment differs depending on the accounting approach:

• In the +1/-1 approach, both fossil and biogenic methane are valued with a factor of 29.8 kgCO₂e/kg, which takes into account the climate impact of methane over 100 years. It is assumed that the greenhouse effect of the gas remains the same, regardless of whether the carbon originally comes from fossil or biogenic sources.
  
  
• A distinction is made in the 0/0 approach: Fossil methane is also recognised at 29.8, but biogenic methane at only 27 kgCO₂e/kg. As the methane comes from a biogenic source and ultimately oxidises to biogenic CO₂, which is not taken into account as an emission in the 0/0 approach, this reduces the accumulated climate impact over 100 years compared to fossil methane.
  
  

The following table shows examples of how different standards assess biogenic and fossil methane as well as other carbon fluxes. While ISO 14067 uses the +1/-1 approach for biogenic CO₂ fluxes, it adopts the GWP values from the IPCC report for methane - i.e. 29.8 for fossil methane and 27 kgCO₂e/kg for biogenic methane. In the IPCC report, the Intergovernmental Panel on Climate Change publishes the current state of climate research and provides globally recognised emission factors and GWP values based on the 0/0 approach. The ReCiPe methodology also uses a 0/0 approach and therefore does not take biogenic CO₂ emissions into account, but uses the values from an older IPCC report for fossil and biogenic methane. The PEF (Environmental Footprint 3.1) also differentiates depending on whether carbon comes from soil, biomass or methane emissions. For companies, this means that accounting is complex and only those who know the underlying standard can correctly categorise and effectively communicate statements about emissions.

Biogenic carbon in the balance sheet? 5 questions for a quick assessment 

• Do you use biogenic materials?
  (e.g. wood, cotton, paper, bioplastics, vegetable oils, animal fibres)
  
  
• Does your product have a long service life (e.g. as a building material)?
  
  
• Do you have data on the origin of the biomass?
  → Land use changes can significantly worsen your balance sheet
  
  
• Do you want to create a CO₂ balance sheet for your product in accordance with ISO 14067, an LCA in accordance with ISO 14040/14044 or an Environmental Product Declaration (EPD) in accordance with EN15804?
  
  
• Are you planning a cradle-to-gate balance sheet?

If these questions apply to you, it is advisable to take a closer look at the carbon in your product. This is because choosing the right methodology brings benefits – both for your carbon footprint and for communication with customers and in marketing. By choosing the right methodology and providing transparent information about the carbon content of your products, you can not only make your company more environmentally friendly in the long term, but also gain the trust of your customers. Utilise the advantages of a precise and comprehensible sustainability balance sheet and set a strong signal for the future of your company.

Would you like to create or improve your CO₂ balance?
Get in touch with us – we will be happy to advise you in a non-binding initial consultation.

Or carry out our free sustainability check for your company!

Text: Hannah Zachskorn