Biogenic carbon and the CO₂ balance: is biomethane climate neutral?

CO₂ released when biomethane is burned is biogenic carbon dioxide: the carbon comes from biomass that took it from the atmosphere in recent years, so in EU methodologies emissions from the use of biomass fuels are counted as zero (e_u = 0), and the balance covers other components: cultivation, processing, transport, methane, N₂O and land-use change. The climate "neutrality" of biomethane therefore does not follow from the biogenic nature of the CO₂ alone, but from the whole balance, in which methane leaks, N₂O emissions and the origin of the feedstock are of great importance.

The carbon cycle and the accounting convention

Plants fix CO₂ in photosynthesis, and the decomposition or combustion of biomass returns it to the atmosphere. If this takes place within a short time (annual plants, wastes, manures), no additional carbon enters the atmosphere in net terms, unlike fossil fuels, which extract carbon from millions of years ago. In national inventories under the IPCC guidelines, CO₂ emissions from burning energy biomass are not counted in the energy sector but recorded in the land use and forestry sector, in order to avoid double counting; in EU law this rule is carried over into the sustainability methodology.

Where neutrality is less obvious

For this reason RED sets sustainability criteria for biomass (including protection of land with high nature value) and emission reduction thresholds.

Methane, N₂O and energy: what really dominates

At a biogas plant, the emissions that really weigh on the balance are: methane leaks (slip, digestate, leaks), N₂O from fertilisation and digestate application, and CO₂ from fossil energy used in the process (electricity, heat, transport). For example, 1 t of leaked methane corresponds to 28 t CO₂e (GWP₁₀₀ = 28), so a loss of 1% in an installation producing 2.2 million m³ CH₄ (22 thousand m³ ≈ 15.8 t) is about 440 t CO₂e per year – many times more than the dozen or so tonnes of CO₂ from energy used in some systems. In turn, the biogenic CO₂ from burning 2.2 million m³ CH₄ is about 4300 t per year (2.2 million × 1.98 kg/m³), but by convention it is not added to the balance.

Biogenic CO₂ as a resource

The CO₂ stream from biogas upgrading is biogenically clean. It can be:

1. released into the atmosphere (conventionally neutral),
2. used (CCU) in the food industry, greenhouses, e-fuels,
3. stored in deep geological formations (CCS), which leads to the removal of CO₂ from the atmosphere (so-called BECCS or BiCRS).

In the third variant the biomethane balance can become negative, because in addition to avoiding fossil emissions, CO₂ is removed from the atmospheric cycle. Regulation (EU) 2024/3012 creates a framework for voluntary certification of carbon removals, facilitating the transparency and credibility of such actions.

Good accounting practices

• Separate biogenic from fossil CO₂ in reports.
• Give methane and N₂O emissions separately, with the GWP and time horizon.
• Indicate which methodology (RED, GHG Protocol) you use.
• For countries reporting under the IPCC guidelines, remember to record biomass emissions in the LULUCF sector.

The most common misconceptions

The first misconception: "biogas is always neutral". In reality, a poorly run installation with methane leaks can have a larger footprint than assumed. The second: "CO₂ from upgrading does not matter". It does, because its utilisation (sale, storage) is an opportunity to lower the balance. The third: "biomass is always renewable". Only biomass meeting the sustainability criteria is recognised in EU mechanisms. A clear, complete balance protects against accusations of greenwashing.

Significance for customers

Industrial customers who buy biomethane in order to reduce Scope 1 emissions increasingly require suppliers to provide detailed data on the carbon footprint, and not only a declaration that the gas is biogenic. In sustainability reports, biogenic and fossil emissions are separated, and the supplier should be able to indicate the methodology and data sources.

Summary

Biomethane can be very beneficial for the climate, but not because "CO₂ is biogenic" – rather because it replaces a fossil fuel and prevents methane emissions, provided the installation is leak-tight and well run. An honest assessment requires a full balance, not one component.