In 2026 Q3, new biogenic carbon flows were added to the Federal Elementary Flow List (FEDEFL). Recommended approaches to modeling with these flows are provided below.
Two accounting approaches¶
For simplified modeling, carbon that is sourced from the atmosphere which is re-emitted in the short term[1] is assumed to have net zero emissions. That is, biogenic emissions have a GWP characterization factor (CF) of 0, and input resource flows of biogenic carbon have a CF of 0. Long-term sequestration is modeled using
emission / groundflowables with a CF of -1. This is referred to as the 0/0 approach in this document.Carbon is removed from the atmosphere during photosynthesis (with a CF of -1) and re-emitted during combustion or decomposition (with a CF of +1). This is referred to as the -1/+1 approach in this document.
By default, all LCIA methods will be made available using the 0/0 approach for the FLCAC. Versions using the -1/+1 approach will be made available in the future. Data providers are encouraged to model their flows to facilitate the use of the -1/+1 approach, and to indicate when that is not feasible. In doing so, the 0/0 approach will also be applicable.
Flow characterization¶
Carbon dioxide and carbon dioxide, biogenic resource flows must always be paired with their corresponding emission flow to arrive at a correct, net characterization. For example, carbon dioxide resource flows cannot be paired with carbon dioxide, biogenic emission flows because the carbon source reservoirs and accounting approaches differ.
Characterization factors for carbon dioxide are identical for both accounting methods.
Biotic resource flows such as carbon / resource / biotic are not characterized and cannot be used directly for GWP accounting.
Carbon dioxide and carbon dioxide, biogenic / emission / water flows are available, but are not characterized in any GHG method and are generally not recommended for use under the assumption that any CO2 dissolved in water is likely to reach equilibrium and enter the atmosphere.
Table 1:Carbon dioxide flow characterization
| Flow direction | Compartment | Flow | ||
|---|---|---|---|---|
| Carbon dioxide synonym: "carbon dioxide, fossil" | Carbon dioxide, biogenic synonym: "carbon dioxide, non-fossil" | Carbon dioxide, land use change synonym: "carbon dioxide, from soil or biomass stock" | ||
| Input | Resource/ground | GWP: 0 | GWP 0/0: +1 [1] GWP -1/+1: 0 | n.a. |
| Use: Track carbon content in fossil fuels, peat or underground CO2 reservoirs. | Use: Track biogenic C extracted from soil. Uncommon. | |||
| Subcompartment(s): only use resource/ground/subterranean | ||||
| Resource/air | GWP: -1 | GWP 0/0: 0 GWP -1/+1: -1 | n.a. | |
| Use: Anthropogenic sequestration (e.g., direct air capture) | Use: Track carbon incorporated in living things (e.g., photosynthesis). | |||
| Subcompartment(s): resource/air/troposphere (preferred) | Subcompartment(s): resource/air/troposphere (preferred) | |||
| Output | Emission/air | GWP: +1 | GWP 0/0: 0 GWP -1/+1: +1 | GWP: +1 |
| Use: Fossil combustion emissions | Use: Track biogenic emissions (e.g. combustion or decomposition). | |||
| Use: Track emissions from direct and indirect land use change. | ||||
| Emission/water | GWP: not characterized | GWP: not characterized | n.a. | |
| Use: Track the quantity of CO2 emitted to air. | Use: Track the quantity of CO2 emitted to air. | |||
| Emission/ground | GWP: 0 | GWP 0/0: -1 GWP -1/+1: 0 | n.a. | |
| Use: Underground sequestration. Assume permanence, else report emissions to air. | Use: Model underground sequestration or storage in long-term soil carbon. Assume permanence, else report emissions to air. | |||
| Subcompartment(s): emission / ground / subterranean | Subcompartment(s): Underground storage - emission / ground / subterranean Soil storage - emission / ground / {terrestrial or human-dominated} | |||
[1] Why is `carbon dioxide, biogenic / resource / ground` a +1 (in 0/0 method)? In this simplified modeling approach (biogenic emissions = 0), carbon removed from the ground must be offset by the credit earned when it is returned to the ground via `carbon dioxide, biogenic / emission / ground`. Inventory will need to be adjusted if carbon is stored in a product for a given study scope. | ||||
Examples of modeling approach¶
Combustion of bio-energy or bio-materials Carbon dioxide is removed from the atmosphere via photosynthesis during crop growth, assigned to
carbon dioxide, biogenic / resource / air. When it is combusted, it is assigned ascarbon dioxide, biogenic / emission / air. These are either both assigned a CF of 0 or a -1 / +1, respectively, depending on the approach used.Carbon capture and sequestration of a fossil-based fuel The portion of sequestered carbon dioxide should be assigned to
carbon dioxide / emission / ground / subterranean(CF of 0).Carbon capture and synthetic e-fuel production During the carbon capture stage, carbon dioxide emissions to air are reduced as they are instead captured as an intermediate flow. In subsequent processing stages that carbon dioxide remains as an intermediate flow until the e-fuel is combusted as
carbon dioxide / emission / air. Specific modeling decisions regarding allocation of any carbon dioxide emissions to specific unit processes may require adjustments to this approach by the practitioner.Cement production The calcination process that occurs during pyroprocessing in the cement kiln decomposes the calcium carbonate (limestone, CaCO3) into calcium oxide (CaO) and carbon dioxide (CO2). Additionally, the pyroprocessing step requires fuels that typically release about the same amount of CO2 as the calcination process. In both cases,
carbon dioxide / resource / groundflows can be used to track carbon content in calcium carbonates and kiln fuels.Carbon dioxide / emission / airflows should be used to track all emissions.Cement carbonation is the passive uptake of atmospheric CO2 reacting with calcium hydroxide (Ca(OH)2, a byproduct of hydration resulting from imperfect reaction, within the cement paste (typically within a concrete structure). The
carbon dioxide / resource / air / troposphereflow can be used to model sequestration of atmospheric carbon in cement. The process of carbonation can last many years and calcium hydroxide is a minor component of Portland cement. Additionally, not all calcium hydroxide in cement will capture CO2 from the air due to surface area and airflow restrictions within the concrete, thus the captured CO2 is a moderate fraction of CO2 released in production.Marine sequestration Numerous strategies are being explored for sequestration of carbon within the ocean such as deep-ocean injection, alkalinity enhancement, or ocean fertilization. For simplicity and due to the limited availability of oceanic subcompartments within the FEDEFL, we recommend using
emission / groundflows to model marine sequestration. Include exchange descriptions to describe the mode of carbon capture that is reflected.Bio-energy carbon capture and sequestration (BECCS) The portion of carbon dioxide sequestered should be assigned to
carbon dioxide, biogenic / emission/ ground/ subterranean. In the 0/0 accounting method, the resource flow has a CF of 0 and the emission / ground flow has a CF of -1. Alternatively, in the -1/+1 approach, the portion that is stored has a CF of 0, the portion that is emitted to air has a CF of +1, while an offsettingcarbon dioxide, biogenic / resource / airflow has a CF of -1.Direct air capture Carbon that is removed from the atmosphere can be tracked as
carbon dioxide / resource / air(CF of -1). When it is sequestered usecarbon dioxide / emission / ground / subterranean(CF of 0).Long-term soil carbon amendments can be modeled using the
carbon dioxide, biogenic / emission / ground / terrestrialorhuman-dominatedflows. In the 0/0 accounting method, a CF of 0 will be assigned tocarbon dioxide, biogenic / resource / airflows used to model incorporation in plants via photosynthesis. Thecarbon dioxide, biogenic / emission / groundflows can be used to model the fraction of carbon retained in soil for greater than 100 years (in the case of GWP-100), and will be assigned a CF of -1. The portion of carbon in soil amendments that decomposes in less than 100 years should be modeled ascarbon dioxide, biogenic / resource / airwhich is assigned a CF of 0, resulting in net zero impact for the re-emitted fraction of fixed carbon. Using the -1/+1 approach, sequestration is logged when using thecarbon dioxide, biogenic / resource / airflow (CF of -1). The portion of re-emitted carbon (emission / air) is assigned a CF of +1, resulting in net zero impact. Long term storage is modeled using thecarbon dioxide, biogenic / emission / groundflows and is assigned a CF of 0.Emissions from land use change Changes in land use practices can result in pulses of carbon emissions from above- or below-ground biomass. The
carbon dioxide, land use change / emission / airflow is available for separate tracking of these emissions as prescribed in ISO 21930 and to avoid confusion with other emissions of biogenic carbon to air.Landfill Storage Long-term storage of biogenic carbon in landfills may be modeled using
carbon dioxide, biogenic / emission / groundfor the fraction of carbon retained in the landfill for greater than 100 years (in the case of GWP-100).
There is not complete agreement between different standards and LCIA methods regarding what represents short-term, though < 100 years is a common benchmark.