GHG quantification

General GHG quantification rules can be found in the Rainbow Standard Rules.

Calculations of GHG emissions for the baseline and project scenarios shall follow a robust, recognized method and good practice guidance. The overall methodological approach is a comparative life cycle assessment (LCA) at the project-scale, based on .

Functional unit

The functional unit shall be 1 tonne of crushed rock/mineral applied to the soil.

System boundary

Net CDR shall be calculated for each reporting period as the following, where $P$ signifies the project scenario/treatment plots, and $B$ signifies the baseline scenario/control plots:

\textbf{(Eq.1)}\ Net_{CDR} = Project_{CDR}- Baseline_{CDR} -Project_{emissions}

Where,

$Net_{CDR}$ represents the net carbon removals caused by project in the reporting period, in $tCO_2eq$ , and equals the amount of removal RCCs to issue.
$Project_{CDR}$ represents the net CDR from the Project Scenario, in $tCO_2eq$ , calculated in Equation 2.
$Baseline_{CDR}$ represents the net CDR from the Baseline scenario, in $tCO_2eq$ , calculated in Equation 10.
$Project_{emissions}$ represents the induced emissions caused by the project, in $tCO_2eq$ , is calculated in Equation 3.

Project scenario

The net CDR from the project scenario is determined by measuring the CDR gains in the (NFZ) ( $NFZ_{P,\ net\ removal}$ ), and subtracting the CDR losses in the (FFZ) ( $FFZ_{P,\ loss}$ ) and the GHG emissions from upstream and onsite activities ( $Project_{emissions}$ ), using the following equations:

\textbf{(Eq.2)}\ Project_{CDR} = NFZ_{P\, net\ removal}-FFZ_{P\, loss}

Where,

$Project_{CDR}$ was described in Equation 1.
$NFZ_{P\, net\ removal}$ represents the net gain in carbon removal measured in the project/treatment area's NFZ in $tCO_2eq$ , detailed in sections Method 1: Direct measurement of export and Method 2: Mass balance. Project Developers shall choose one of the the two methods shall be used to quantify the amount of CDR occurring in the NFZ. It is calculated in Equation 4.
$FFZ_{B\, loss}$ represents the loss/reversal of carbon removal in the project FFZ in $tCO_2eq$ , detailed in the section Project FFZ loss.

\textbf{(Eq.3)}\ Project_{emissions} = E_{extraction}+E_{processing}+E_{transport}

Where,

$Project_{emissions}$ represents the induced emissions caused by the project, in $tCO_2eq$ .
$E_{extraction}$ represents the induced emissions caused by extraction of feedstock in the Project Scenario, in $tCO_2eq$ , detailed in the Project induced emissions section, and calculated in Equation 7.
$E_{processing}$ represents the induced emissions caused by processing of feedstock in the Project Scenario, in $tCO_2eq$ , detailed in the Project induced emissions section, and calculated in Equation 8.
$E_{transport}$ represents the induced emissions caused by transport of feedstock in the Project Scenario, in $tCO_2eq$ , detailed in the Project induced emissions section, and calculated in Equation 9.

NFZ Method 1: Direct measurement of export

NFZ removal is calculated by measuring the export of carbonate alkalinity exceeding a counterfactual baseline, integrated across the duration of the reporting period.

Specifically, this is calculated by combining alkalinity concentrations—derived from a time series of in-situ measurements of porewater or drainage water—with water flux measurements at the NFZ boundary of the project/treatment plot, and comparing them to corresponding measurements from a representative baseline/control plot.

This is achieved through aqueous-phase measurements in each reporting period

What to measure

carbonate system parameters (e.g. alkalinity, DIC)

major ion concentrations (e.g. base cations $Ca^{2+},\ Mg^{2+}$ , major anions)

See the Measurements and data sources section for details on which measurements may be used.

Where to measure

Either of the measurements listed on the left can be measured in:

soil porewater at the end/depth of the NFZ

drainage or catchment waters beyond the NFZ

The specific NFZ boundary is defined by the site hydrology, detailed in the Site Characterization section.

Sampling requirements for aqueous phase samples are described in the Number of aqueous samples per strata section.

Both project and baseline (i.e. treatment and control plot) NFZ removal ( $NFZ_{net\ removal}$ ) shall be calculated according to the following equations.

Calculations: NFZ removal Method 1: Direct measurement of export

All terms have a spatial scope of the NFZ and a temporal scope of one reporting period, and have units of tCO $_2$ eq.

$\textbf{(Eq.4)}\ NFZ_{P,\ net\ removal} = \sum_{time} CDR_{export,\ NFZ}$

Where

$NFZ_{P,\ net\ removal}$ is described in Equation 2, and represents the net CDR occurring in the NFZ during the reporting period for the project scenario (i.e. treatment plots).
$CDR_{export,\ NFZ}$ represents the sum of measured alkalinity export from the NFZ, time-integrated over the reporting period. Further details on how to measure each component are presented in the Measurements and data sources section.

NFZ Method 2: Mass balance

In this method, the potential maximum CDR from alkalinity release from the feedstock is measured in each reporting period, along with adjustments to net CDR based on changes in soil inorganic carbon stocks. These adjustments account for:

Cation uptake in biomass
Cation retention on sorption sites
Secondary carbonate formation, and
Alkalinity that is not charge balanced by bicarbonate.

NFZ removal is calculated using Equation 5, following these steps in each reporting period:

Measure base cation release

Base cations released from feedstock dissolution are measured during the reporting period.

Calculate potential CDR

The cation release measurements are used to calculate the potential CDR associated with the present reporting period (CDR gains).

Adjust by inorganic carbon changes

Calculated potential CDR is adjusted by considering changes in each potential carbon loss term relative to the previous reporting period. These could result in either CDR loss or additional CDR (positive or negative signs).

After accounting for each carbon loss term, the remaining alkalinity from feedstock dissolution reflects the additional alkalinity that remains in solution and is transported beyond the NFZ into the FFZ, where further CDR loss terms are applied (see Project FFZ loss section).

This method is based mostly on solid soil measurements, but may also include some porewater measurements (see the Feedstock dissolution and Inefficient conversion of alkalinity to CDR sections).

Calculations: NFZ removal Method 2: Mass balance

All terms have a spatial scope of the NFZ and a temporal scope of one reporting period, and have units of tCO $_2$ eq. Details for how to measure each component are presented in the Measurements and data sources section.

$\textbf{(Eq.5)}\ NFZ_{P,\ net\ removal} = CDR_{FD}-CDR_{biomass}-CDR_{Alk\ inefficiency}-CDR_{sorption}-CDR_{carbonate\ precip}$

$NFZ_{P,\ net\ removal}$ represents the net CDR occurring in the NFZ during the reporting period. This is used for both project (treatment) and baseline (control) scenarios. It accounts for both removal and loss of carbon via CDR. It represents the same term as in Equation 5, but is calculated using a different method.
$CDR_{FD}$ represents the increase in CDR as the potential theoretical maximum CDR associated with the measured release and loss of base cations from feedstock dissolution during that reporting period.
$CDR_{biomass}$ represents the permanent decrease in CDR from cation uptake into biomass.
$CDR_{Alk\ inefficiency}$ represents the permanent decrease in CDR from generated alkalinity that is not charge balanced by bicarbonate, for a variety of reasons, ensuring permanent CDR. This is due notably to pH-dependent carbonic acid system speciation; non-carbonic acid weathering from sulfuric, nitric or organic acids; and acid buffering.
$CDR_{sorption}$ represents the temporary decrease in CDR from base cation sorption on soil exchange sites or reductions in exchangeable acidity. This value notably may be positive or negative, suggesting that in a given reporting period there may be a net de-sorption i.e. addition of base cations to the soil.
$CDR_{carbonate\ precip}$ represents the change in CDR from the precipitation of secondary carbonate minerals in the NFZ.

Changes in soil organic carbon (SOC) are currently not required for carbon credit issuance due to high uncertainty, yet may be important for gains or losses in CDR and soil health. Rainbow is actively monitoring research on this topic, and may add SOC measurement requirements in future versions of this methodology.

Project FFZ Loss

FFZ losses shall be considered in surface water and surface oceans (see Equation 6). The project site's specific hydrology, with expected flow paths and residence times, shall be taken into account, according to the Site Characterization Report.

FFZ losses are expected to occur over thousands of years; however, for the purposes of RCC issuance, they must be estimated upfront based on the total potential CDR and proportionally allocated across reporting periods according to the amount of CDR reported and credited. These losses shall be amortized and accounted for using the same approach applied to upstream project emissions, as described below.

If Project Developers can prove that weathering products will not pass through surface water, and will instead travel straight to groundwater and then the ocean, then the surface water CDR loss may be omitted.

As detailed in the Site characterization section, Project Developers shall describe the expected final CDR reservoir, indicating whether carbon is ultimately stored as bicarbonate ions in the ocean or as carbonate minerals within the watershed. If carbonate minerals are a significant reservoir, developers must assess the risk of strong acid weathering of this carbonate; if the risk is high, it must be accounted for as a deduction in the project's CDR through the Reversal Risk assessment.

Calculations: FFZ loss

All terms have a temporal scope of 1000 years, and are allocated to reporting periods proportionally to the amount of CDR reported. All terms have units of tCO $_2$ eq. Details for how to measure each component are presented in the Measurements and data sources section.

$\textbf{(Eq.6)}\ FFZ_{P,\ loss} =CDR_{surface\ water}+CDR_{surface\ ocean}$

Where

$FFZ_{loss}$ represents the total losses of CDR expected for the entire amount of spread rocks.

$CDR_{surface\ water}$ represents the CDR loss due to permanent alkalinity sinks and CO $_2$ evasion in surface waters, such as rivers and lakes (see the Surface water FFZ section below for details).
$CDR_{surface\ ocean}$ represents the CDR loss due to permanent alkalinity sinks and carbonic acid system re-equilibration in the ocean (see the Surface ocean FFZ section below for details).

Project induced emissions

System boundary

The project system boundary shall include the following processes:

Mining and extracting feedstock. This shall be omitted if it is proven that the feedstock is waste from other mining activities. Feedstock shall be considered waste if it has no economic value and would not have been used otherwise. Emissions from the following activities shall be included:

Electricity production
Fuel production and combustion
Water provisioning
Material production and waste treatment
Equipment production and waste treatment

Any process that is shown during a screening LCA to have contribute than 1% of the total induced emissions and removals may be excluded, up until the cumulative excluded processes exceed 3% of total induced emissions and removals.

Temporal allocation of project emissions

Project emissions shall be allocated across the reporting periods. This allocation shall be done in a way that ensures that all upstream emissions are accounted for within the first 50% of potential CDR (as modeled from Potential CDR over the project lifetime calculations, described in the Feedstock characterization section). The distribution may be done proportionally to the amount of CDR completed/credits issued in each reporting period, or may be done more upfront to incur the induced emissions early on to reduce uncertainty later.

For example, if the project's estimated CDR potential is 1,000 tCO $_2$ eq over 10 years, with the following repartition:

Year 1: 100 tCO $_2$ eq
Year 2: 300 tCO $_2$ eq
Year 3: 200 tCO $_2$ eq
Year 4: 100 tCO $_2$ eq
Year 5-10: 50 tCO $_2$ eq/year

Then the 50% mark is 500 tCO $_2$ eq, which the project is expected to reach in reporting period of year 3.

The project's upstream emissions represent 100 tCO $_2$ eq.

These 100 tCO $_2$ eq shall be allocated across the first 500 credits issued, expected to occur within the first 3 years of the project. They may be allocated proportionally over the amount of CDR reported in that period, following:

Year 1: 100/500 = 20% of induced emissions allocated to this reporting period = 20 tCO $_2$ eq
Year 2: 300/500 = 60% of induced emissions allocated to this reporting period = 60 tCO $_2$ eq
Year 3: 100/500 = 20% of induced emissions allocated to this reporting period = 20 tCO $_2$ eq

The actual rate and amount of CDR may differ from the initial estimates. The allocation of upstream emissions shall always aim to be counted within the first 50% of estimated CDR, and the actual year in which this is realized may vary, coming earlier or later than initially estimated. Project Developers should anticipate this and incur their induced emissions accordingly/conservatively.

Calculations- Project emissions

Project induced emissions shall be calculated using Equation 4 above. Each term in Equation 3 is calculated using the following

$\textbf{(Eq.7)}\ E_{\text{Extraction}} = \sum (\text{Amount}_i \times EF_i)$

Where,

$E_{\text{extraction}}$ represents the emissions from all relevant processes related to feedstock extraction.
$Amount_i$ represents the amount of the input/emission of type $i$ , in the same units as the emission factor.
$EF_i$ represents the emission factor for the input/emission of type $i$ in kg CO $_2$ eq per given unit from ecoinvent (see Appendix 1 for ecoinvent database options).

$\textbf{(Eq.8)}\ E_{\text{processing}} = \sum (\text{Amount}_i \times EF_i)$

Where,

$E_{\text{processing}}$ represents the emissions from all relevant processes related to feedstock processing.
$Amount_i$ and $EF_i$ are described in Equation 7.

$\textbf{(Eq.9)}\ E_{\text{transport}} = E_{transport\ energy}+E_{transport\ embodied}$

Where,

$E_{\text{transport\ energy}}$ is calculated using the equations in the Transportation module from the BiCRS methodology, using either the Energy amount, Energy efficiency or Distance based approach.
$E_{transport\ embodied}$ is calculated using the equations in the Transportation module from the BiCRS methodology, from the Embodied emissions section.

Baseline scenario

The baseline scenario shall represent the conditions or practices that would occur in the absence of the project. Only removals are considered in the baseline scenario, not induced emissions, to ensure that the project is only credited for removals it causes beyond business-as-usual removals that would have happened anyway. This includes changes in CDR due to:

use of pH adjusting products on agricultural fields where feedstock is spread (e.g. agricultural lime)
cropping and tillage on agricultural fields where feedstock is spread
fertilizer use on agricultural fields where feedstock is spread
irrigation on agricultural fields where feedstock is spread
weathering in waste feedstock piles

This is calculated using:

\textbf{(Eq.10)}\ Baseline_{CDR} = NFZ_{B\, net\ removal}+Feedstock_{B,\ removal}-FFZ_{B\, loss}

Where,

$NFZ_{B\, net\ removal}$ represents the net gain in carbon removal measured in the baseline/control area's NFZ in $tCO_2eq$ , measured using the same approach as in the Project Scenario, detailed in section Baseline NFZ.
$Feedstock_{B,\ removal}$ represents the net gain in carbon removal measured in the business as usual management of the rock feedstock used in the project (if it is waste rock), in $tCO_2eq$ , detailed in section Baseline Feedstock CDR.
$FFZ_{P\, loss}$ represents the loss/reversal of carbon removal in the baseline FFZ in $tCO_2eq$ , detailed in the section Baseline FFZ loss.

By default, the overall structure of the baseline scenario for a given project is valid for the entire crediting period. This may change if the Project Developer informs Rainbow of a material change in their operations or in baseline conditions, and/or if the methodology undergoes revisions that change the baseline scenario. Note that the actual values in the baseline scenario are updated in each reporting period.

Baseline NFZ

Spreading of pH adjusting products (e.g. agricultural lime) to agricultural fields can result in either CDR gains, losses, or neutral effects, or several different effects at different times in the process (e.g. short-term losses but long-term gains). ERW projects shall only be issued removal credits for the removals they cause beyond any baseline CDR gains.

To account for this, control plots are managed and monitored to measure CDR gains ( $NFZ_{B,\ net\ removal}$ ) that would have occurred in absence of the project, to deduct from the project CDR. Quantification of baseline CDR in the NFZ on fields shall be done by:

NFZ in a BAU control plot: applying NFZ method 1 or NFZ method 2 to the baseline/control plots to measure and calculate $NFZ_{B,\ net\ removal}$ . The same Method must be chosen for both the control and treatment plots. and
NFZ in a negative control plot: assume that all agricultural lime that would have been used generates CDR at 100% efficiency with nearly no CDR loss

See the Control plot section for more details on how to set up, justify, and monitor control plots.

Baseline NFZ results shall only be included in the project net CDR quantification if they result in CDR gain (i.e. if the value is negative). If the use of agricultural lime in the baseline scenario is determined to be a net source of emissions, it's value shall be considered 0 tCO2eq, to ensure avoided emissions from liming are not counted towards project CDR.

If negative control plots are used, it shall be conservatively assumed that all agricultural lime that would have hypothetically been used (e.g. using regional statistics or historical records) dissolves and generates CDR at 100% efficiency, with negligible carbon loss terms.

Only loss from non-carbonic weathering adjustments may be considered, using the same assumptions and calculations as in the project scenario/treatment plots.

This baseline CDR should be subtracted from the project CDR in the reporting period when the agricultural lime spreading would have occurred.

Baseline FFZ loss

Loss of CDR from processes in the FFZ ( $FFZ_{B,\ loss}$ ) shall be calculated by applying the same models, calculations and assumptions from the Project FFZ loss section to the control plots.

Baseline feedstock CDR

The baseline scenario shall also consider CDR from the alternative fate of feedstock ( $Feedstock_{B,\ removal}$ ), if the project uses waste feedstock e.g. from mining, that would have otherwise been stored and exposed to the atmosphere and driven CDR.

Project Developers shall

Describe the alternative fate of feedstock.
If waste, characterize the feedstock's inorganic carbon content, mineral and waste handling practices, and expected storage conditions.
Explain assumptions around if/how this storage leads to baseline CDR.
Justify any expectations of zero ambient weathering from the mineral feedstock.

If baseline weathering is not assumed to be zero, Project Developers shall model CDR from baseline weathering for the surface layer of feedstock, considering the same factors described in the Feedstock Characterization section, plus the environmental conditions where feedstock is stored (e.g. rainfall, temperature...). If it is estimated based on a preliminary LCA and modeling results to be <1% of emissions, it may be omitted, per the Rainbow Standard Rules.

Data sources

The required primary data are presented in Tables 1-4. These data may be estimated for ex-ante validation, and should updated with real production values and proof for ex-post verification depending on the data type, and shall be made publicly available. Additional data sources for processes not explicitly listed should be added if they are within the 1% cutoff threshold mentioned above.

Table 1 Summary of primary data related to project emissions needed from projects and their source for initial project certification and validation. Several data points need to be updated annually during verification if the upon a successive spreading events (see Monitoring Plan section).

Parameter

Unit

Source

Detailed process diagram with included/excluded processes

Flow chart

Internal process documents

Waste status of feedstock

Text description

Contract with feedstock provider, receipts, invoices

Energy amount and type for feedstock extraction

kWh, MJ, liters

Operating records, machinery/equipment tracking, invoices, bills, receipts

Energy amount and type for feedstock processing

kWh, MJ, liters

Operating records, machinery/equipment tracking, invoices, bills, receipts

Energy amount and type for feedstock spreading

kWh, MJ, liters

Operating records, machinery/equipment tracking

Transport data: delivery of feedstock to spreading site

t*km, or
liters, kg, MJ of fuel

See the Transportation module from the BiCRS methodology for more details

Type of other input/emission*

Text description

Internal process documents

Amount of other input/emission*

kg, liter, kWh, MWh, GWh, m $^3$

Meter readings, bills, internal tracking documents, invoices, contracts, gas analyzers or sensors on pyrolysis equipment, calculated using conversions from other primary project data

The version 3.11 (hereafter referred to as ecoinvent) shall be the main source of emission factors unless otherwise specified. Ecoinvent is preferred because it is traceable, reliable, and well-recognized. The ecoinvent processes selected are detailed in Appendix.

If the available emission factors do not accurately represent the project, a different emission factor may be submitted by the Project Developer, and approved by the Rainbow Certification team and the VVB. Any emission factor must meet the data requirements outlined in the Rainbow Standard Rules, and come from traceable, transparent, unbiased, and reputable sources.

The following tables summarize the required primary data for calculating net carbon removal gains and losses in the NFZ and FFZ. The specific measurement approaches used may differ by project and must be clearly described in the PDD, and are detailed in the Sampling and measurements section.

It is recommended that the values selected for CDR quantification represent either:

the lower bound of a two-sided 80% confidence interval (for frequentist approach), or
the 10th percentile of a posterior distribution (for Bayesian models).

If these are not used, higher uncertainty is assumed and a larger discount factor should be applied.

Table 2 Primary data needed to calculate net carbon removals for all projects, regardless of the NFZ measurement method chosen.

Parameter

Unit

Source

FFZ loss surface waters: permanent alkalinity sinks

%, fraction, or kgCO₂eq

Modeled results, accounting for site-specific hydrology

FFZ loss surface waters: CO $_2$ evasion in surface waters

%, fraction, or kgCO₂eq

Modeled results, accounting for site-specific hydrology

FFZ loss ocean: permanent alkalinity sinks

%, fraction, or kgCO₂eq

Modeled results, accounting for site-specific hydrology

FFZ loss ocean: CO $_2$ evasion in surface waters

%, fraction, or kgCO₂eq

Modeled results, accounting for site-specific hydrology

Table 3 Primary data needed to calculate net carbon removals for projects using NFZ Method 1: Direct measurement of export.

Parameter

Unit

Source

Alkalinity export from the NFZ, time integrated over the reporting period, converted to kgCO₂eq

kgCO₂eq

Primary measurements, data analysis, and further conversions

Table 4 Primary data needed to calculate net carbon removals for projects using NFZ Method 2: Mass balance.

Parameter

Unit

Source

CDR gains from feedstock dissolution and export of base cations from NFZ, converted to kgCO₂eq

kgCO₂eq

Primary measurements, data analysis, and further conversions

CDR loss from biomass uptake of base cations, converted to kgCO₂eq

kgCO₂eq

Primary measurements, data analysis, and further conversions

CDR loss from non-carbonic acid weathering, converted to kgCO₂eq

kgCO₂eq

Primary measurements, data analysis, and further conversions

CDR loss from acid buffering, converted to kgCO₂eq

kgCO₂eq

Primary measurements, data analysis, and further conversions

CDR gain or loss from base cation sorption, converted to kgCO₂eq

kgCO₂eq

Primary measurements, data analysis, and further conversions

CDR gain or loss from secondary carbonate formation, converted to kgCO₂eq (optional)

kgCO₂eq

Primary measurements, data analysis, and further conversions

Models

Models may be used for several components in this methodology. The uses of models include:

Feedstock dissolution for ex-ante calculations, estimating provisional credit volumes, and creating expected timeline of weathering and crediting (required)
Groundwater flow path and residence time models (required)
Hydrological flow path, determining which ocean basin weathering products will end up in (required)
FFZ loss models (rivers and oceans)
- surface water carbonate mineral burial (required if maximum in immediate discharge basin is > 1)
- ocean outgassing (optional, may be conservatively calculated using simple conversions instead)

Models used shall be transparently described in the PDD, including a description of the overall structure of the model, key sources/references, assumptions, input data, and secondary/fixed data used.

The use of models beyond the requirements and outside the purpose of crediting (e.g. reactive transport models) is encouraged for the advancement of the scientific field, and to facilitate model use in MRV in the future, but is not required for carbon credit issuance. See the co-benefits section on how this work is accounted for.

Assumptions

When calculating $CDR_{FD}$ (the increase in CDR as the potential theoretical maximum CDR associated with the measured release and loss of base cations), it is assumed that all base cations released through feedstock dissolution are fully charge-balanced by bicarbonate (HCO₃⁻). This is later adjusted in the Inefficient conversion of alkalinity to CDR term.
Organic acids are assumed to degrade after reacting with silicate minerals, producing dissolved inorganic carbon (DIC) equivalent to that from carbonic acid weathering.
It is assumed that no net CDR gains occur in the FFZ; only potential losses are considered, a conservative approach that may underestimate CDR in acidic soils where feedstock dissolution is high.
Secondary silicate and carbonate precipitation are already accounted for through integrated weathering DIC export measurements in NFZ Method 1 and full-depth solid-phase soil assessments of feedstock dissolution in NFZ Method 2.

Uncertainty assessment

See general instructions for uncertainty assessment in the Rainbow Standard Rules. The outcome of the assessment shall be used to determine the percent of avoided emissions to eliminate with the .

The following assumptions have low uncertainty:

Calculating $CDR_{FD}$ assumes that all base cations released through feedstock dissolution are fully charge-balanced by bicarbonate (HCO₃⁻)
Organic acids are assumed to degrade after reacting with silicate minerals, producing dissolved inorganic carbon (DIC) equivalent to that from carbonic acid weathering.
Secondary silicate and carbonate precipitation are already accounted for through integrated weathering DIC export measurements in NFZ Method 1 and full-depth solid-phase soil assessments of feedstock dissolution in NFZ Method 2.

The following assumptions have high uncertainty:

It is assumed that no net CDR gains occur in the FFZ. This is a very conservative assumption that leads to under-crediting.

The baseline scenario selection guidance in this methodology has low uncertainty because it is based on project-specific information and is well known.

The equations presented in this methodology have low uncertainty because they consist of basic operations. The uncertainty in equations used at the project-level to convert measurements into CDR shall be assessed for each project.

No estimates or secondary data are used as a default for projects in this methodology.

Uncertainty of models and measurements shall be assessed at the project level. Project Developers shall justify the statistical methods used to assess uncertainty, such as frequentist approaches, Bayesian approaches, or error propagation, and transparently disclose assumptions, equations and results.

It is recommended that the values selected for CDR quantification represent either

the lower bound of a two-sided 80% confidence interval (for frequentist approach), or
the 10th percentile of a posterior distribution (for Bayesian models).

If these are not used, higher uncertainty and a larger discount factor should be applied.

The minimum uncertainty at the methodology level is estimated to be low. This translates to an expected discount factor of at least 3% for projects under this methodology. Project-specific factors may introduce higher uncertainty and justify higher discount factors for given projects.

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