Biogenic carbon: The decisive factor in your carbon footprint?

Whether in the construction, chemical or agricultural industries - many companies work with biogenic raw materials. But when it comes to carbon footprint calculation, biogenic and fossil carbon differ fundamentally. Depending on the accounting approach, this can lead to significantly different results with consequences for marketing, reporting and sustainability strategies. In this article, you will learn what matters most when it comes to biogenic carbon and how to select a methodology that delivers consistent and comprehensible results.

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

To produce a meaningful and reliable carbon footprint or life cycle analysis (LCA), it is essential to distinguish between fossil and biogenic carbon. Depending on the use case and LCA methodology implemented, the carbon balance and, consequently, the product carbon footprint (PCF) vary considerably. 

Especially when comparing products, mixing different approaches can easily lead to misjudgments. This harbors risks - especially with regard to marketing claims, for instance in the context of the Green Claims Directive. Sound and consistent carbon accounting is therefore vital not only for accurate internal analysis but also for credible and legally compliant communication.

Comparison of carbon accounting approaches

The 0/0 approach

In the 0/0 approach, biogenic carbon is not accounted for: Neither the uptake of CO₂ nor its subsequent release - for example through decay, combustion or use - is included in the balance. This approach assumes that new plant growth compensates for the emissions released in a timely manner, provided that the carbon cycle remains closed and no land-use changes occur.

• Methodologically simple and straightforward
• Less effort required for data collection

• Flawed results in cradle-to-gate balances, as the carbon stored in the products is not taken into account
• Bio-based products can therefore perform worse than fossil-based products

• Used in impact assessment methods according to ReCiPe2016 or the product environmental footprint (PEF)
  

The +1/-1 approach

In the +1/-1 approach, biogenic carbon is accounted for in a differentiated manner: CO₂ uptake by plants is recorded as a negative credit (-1) and subsequent release as a positive emission (+1). This takes into account time lags in the carbon cycle and provides a more realistic representation of climate impacts.

• More precise and meaningful representation, especially for biogenic products
• Easier to combine with fossil-based products: biogenic carbon does not have to be tracked throughout the entire supply chain - it is sufficient to account for net emissions at the end of the life cycle.
  

• Greater effort required for data collection
• Increased complexity in terms of data requirements

• Used for PCFs according to ISO 14067 or for environmental product declarations (EPDs) according to EN15804
  

Example: 0/0 vs. +1/-1 approach in direct comparison

Assumption: Two fictional products - one fossil-based, one bio-based - undergo the same manufacturing process with identical CO₂ emissions. As the biogenic CO₂ is not accounted for under the 0/0 approach, the two products do not differ from each other until the end of production: both generate 40 kg of CO₂ emissions up to the "gate". The difference only becomes apparent at the end of the life cycle, as only the fossil carbon is recorded here.

       


Under the +1/-1 approach, however, the advantage of the biogenic material becomes apparent immediately after production. It receives credit for the absorption of CO₂,allowing for improved comparability between the products. This approach is frequently applied to bio-based products where carbon is stored over longer periods, such as wood products, land-use change scenarios, or agricultural and forestry processes.

       

What companies should consider for sound PCFs, CCFs and green claims

Avoiding reporting risks and ensuring consistent carbon accounting

Since there are two different accounting approaches, the 0/0 and the +1/-1 approach, there is a risk that downstream partners will misinterpret the reported carbon balance. This is particularly relevant when +1/−1 results are communicated and incorporated into calculations based on the 0/0 approach without proper conversion. In such cases, the actual PCF may be significantly underestimated. Vice versa, the PCF may also be considerably overestimated if methodologies are mixed in the opposite direction.

To prevent misunderstandings and misleading green claims, it can be helpful to report values both with and without biogenic carbon. This ensures transparent documentation of the underlying accounting approach. Standards such as EN 15804 therefore require not only the declaration of CO₂ emissions, but also the disclosure of the biogenic carbon content.

Assessing biogenic methane correctly and classifying its climate impact

Methane (CH₄) is produced during the fermentation or composting of biogenic materials - e.g. in biogas plants. Although the carbon it contains originally derives from the atmosphere, it is released not as CO₂ but in the form of CH₄. The problem: methane has a significantly higher global warming potential (GWP) than CO₂ and has a significantly greater impact on the climate over a period of 100 years.

After some time in the atmosphere, methane oxidises back to CO₂, which must also be considered in the assessment. This is particularly relevant for biogenic CH₄, as the question arises here: does the original methane count - or the CO₂ it later becomes?

• Under the +1/-1 approach, the global warming potential of both fossil and biogenic methane is considered identical (29.8 kg CO_2e/kg), as the CO₂ formed through the oxidation of CH₄ is accounted for as +1 in both cases. It is assumed that the greenhouse effect of the gas remains the same, regardless of whether the carbon originally stems from fossil or biogenic sources.

• A distinction is made in the 0/0 approach: Fossil methane is also set at 29.8, whereas biogenic methane is assigned only 27 kg CO_2e/kg. Since the methane originates from a biogenic source and ultimately oxidises to biogenic CO₂ – which is not counted as an emission under the 0/0 approach – this reduces the accumulated climate impact over 100 years compared to fossil methane. Consequently, under the 0/0 approach, fossil methane has a higher global warming potential than biogenic methane.

The table below illustrates how different standards assess biogenic and fossil methane, as well as other carbon fluxes. The GWP values are taken from the IPCC report: 29.8 kg CO_2e/kg for fossil methane and 27 kg CO_2e/kg for biogenic methane. Some impact assessment methods, such as ReCiPe, use values from an earlier IPCC report (36.8 and 34 kg CO_2e/kg respectively). In addition, up to version 3.11, there was an error in the ecoinvent database that incorrectly applied the reduced global warming potential for biogenic methane in methods with a +1/-1 approach (e.g. IPCC 2021, ISO 14067, EPDs according to EN15804).

For companies, this means: carbon accounting is complex. Only those who understand the underlying standard can correctly interpret emission figures and communicate them effectively.

Conclusion: the right methodology is more than just arithmetic

Our recommendation: consider the role of biogenic raw materials at an early stage in order to select the appropriate accounting logic. This not only influences your CO₂ figures, but also the credibility and informative value of your reporting and marketing communication. 

A consistent and transparent methodology protects against greenwashing accusations, builds trust among stakeholders and can make a targeted contribution to optimising ESG ratings.

Would you like to calculate or improve your carbon footprint ?

EurA is your partner for sophisticated, industry-quality CO₂ assessments: whether PCF, LCA or EPD - we master complex data models, take regulatory requirements into account and deliver audit-proof results.

Our consultancy combines technical excellence with strategic added value. We analyse your value chain, work with you to select the appropriate methodology and ensure that your carbon footprint is not only robust, but also effective in communication.

Benefit from a precise and comprehensible CO₂ balance and send a strong signal for the future of your company. Find out more here.

FAQ

What is biogenic carbon?

Biogenic carbon comes from organic materials such as plants or biomass that has absorbed CO₂ from the atmosphere. During decomposition or combustion, the CO₂ is released again without increasing the atmospheric concentration in the long term (assuming constant land use).

Why is a distinction made between biogenic and fossil carbon?

Fossil carbon is stored for millions of years and releases additional CO₂ into the atmosphere when burned. Biogenic carbon circulates in a short natural cycle and therefore has climate impacts that need to be assessed differently.

When should I use the +1/-1 approach?

If biogenic materials remain bound in a product over a longer period of time or if the benefits of a bio-based product are to be presented in a cradle-to-gate balance, the +1/-1 approach is more suitable.

How do I choose the right accounting method?

The decisive factors are the use case, the product life cycle, data availability and the reporting objectives. Transparency about the chosen approach is crucial for credibility and comparability. Our experts are here to support you.

Text: Hannah Zachskorn and Levin Winzinger