The first year of corporate emissions reporting is different from every subsequent year, and not because the GHG Protocol methodology changes. What is different is that you are simultaneously building a reporting infrastructure and producing a result for the first time. Every decision you make in year one, which boundary approach to use, which emission factor database to apply, which Scope 3 categories to include, becomes a constraint that the year two and year three reports must either follow or formally restate against.
This is not a reason to delay starting. It is a reason to make year one decisions deliberately, document them clearly, and treat the first report as an infrastructure project as much as a calculation exercise. The checklist below describes the sequence that matters. It is not exhaustive, but it is ordered: skipping earlier steps creates rework in later steps.
Step 1: Establish the Organisational Boundary
Before collecting any data, decide which legal entities and facilities are inside the reporting boundary. The GHG Protocol Corporate Standard offers two primary approaches: operational control (report on facilities where you control operational policies) and equity share (report in proportion to your ownership stake). For most manufacturers with straightforward ownership structures, operational control is the cleaner choice because it aligns with who actually manages the energy and fuel purchasing decisions. Equity share becomes relevant for joint ventures where you hold a partial interest but share operational control with a partner.
Document the boundary decision with a list of specific entities and facilities included, and a brief note on why each is included or excluded. If a leased warehouse is excluded, note the reason. This documentation is not optional: third-party verifiers inspect boundary decisions and require evidence that the boundary is applied consistently across reporting periods. A boundary defined in prose without a facility-level inclusion list is not adequate for verification purposes.
Step 2: Choose the Base Year
The base year is the historical reference point against which future reduction targets are set. It should be a year for which complete and reliable data is available or can be reconstructed. The GHG Protocol recommends choosing a year that is representative of typical operations (not a year disrupted by a plant shutdown, major acquisition, or unusually low production), and one for which the emission data will remain consistent with the reporting boundary as it evolves.
The base year data does not need to be perfect. The GHG Protocol allows for base year recalculation when significant structural changes occur (mergers, divestitures, methodology changes) through documented restatement. What the base year needs to be is reproducible. If the base year calculation was done on a spreadsheet that no one can find, or used factor values that cannot be identified, it cannot be restated when the boundary changes. Build the base year calculation in a form that can be retrieved and replicated three years from now.
For companies starting emissions reporting now, 2023 or 2024 are the most practical base year choices because data is available, disclosure frameworks are treating these as default baseline years in their questionnaire designs, and the emission factor databases commonly used (EMA grid factors, IPCC AR6) have well-documented values for these periods.
Step 3: Identify All Scope 1 Sources Before Collecting Data
The most common year-one Scope 1 error is incomplete source identification: collecting data for the sources you know about (the main natural gas boiler, the largest diesel generator) and missing the ones that are not in the sustainability team's immediate line of sight (the LPG cylinders used in the coating line, the refrigerant top-ups on the cold storage unit, the fugitive losses from on-site compressed gas storage).
Before opening a single invoice, walk through the production footprint with the facilities or engineering team. Ask: what burns fuel on this site? What uses refrigerant? What process gases are purchased? The answer may produce a longer list than expected. Categorise each source: stationary combustion (boilers, heaters, generators), mobile combustion (owned on-site vehicles, forklifts), fugitive emissions (refrigerants, gas leaks), and process emissions if applicable. Then identify what document exists for each. If no document exists, identify the closest proxy or measurement approach.
Step 4: Collect Scope 2 Data and Decide on Method
Scope 2 electricity requires a decision upfront: will you report location-based, market-based, or both? If the company holds renewable energy certificates (I-RECs or equivalent) or has a green tariff agreement, both methods apply and the GHG Protocol requires reporting both when they produce materially different results. If no instruments are held, both methods produce the same number and reporting one with a note is sufficient.
For location-based calculation, collect: meter identifier, consumption in kWh, and billing period for each electricity account. The emission factor comes from the Energy Market Authority grid emission factor for the relevant year. For market-based, additionally collect: I-REC retirement certificates or green tariff documentation, with quantity retired and vintage year. The retirement date needs to match or precede the reporting period close date; retroactive retirements do not count for the market-based calculation in the period they cover.
If the company operates in multiple countries with different utilities and grid factors, the emission factor selection step is more complex but the data collection step is the same: consumption by meter, period, and location.
Step 5: Define Scope 3 Materiality Before Attempting Calculations
Scope 3 is the largest and most complex part of most companies' GHG inventories, and it is the part most often mis-stated in year one. The GHG Protocol Technical Guidance for Companies (2013) lists 15 Scope 3 categories. For a manufacturer, typically material categories are Category 1 (purchased goods and services), Category 4 (upstream transportation), Category 5 (waste generated in operations), and sometimes Category 11 (use of sold products) if the products are energy-consuming.
Rather than attempting all 15 categories in year one, define materiality explicitly: identify which categories are likely to represent more than 1% of total emissions based on the scale of the relevant activity. Document why the other categories are excluded. This materiality assessment, if done honestly and documented, is an acceptable basis for a phased Scope 3 implementation. Attempting all categories with poor data quality produces less reliable results than covering the material categories well.
For Category 1 purchased goods, the choice in year one is almost always spend-based, because activity-based calculation requires supplier-specific emission factors that most companies cannot obtain in the first reporting year. Spend-based means: total spend on goods and services in each procurement category, multiplied by an economy-level emission factor for that category from a database such as EPA USEEIO or Ecoinvent. Document which database was used and which version.
Step 6: Select and Document Your Emission Factor Sources
Emission factors are not universal constants. They vary by source database, by fuel specification, by country or grid region, and by the GWP values used. The choices you make in year one become the baseline for your time series. Using IPCC AR6 GWP values in year one and then switching to AR5 in year two produces a time-series inconsistency that requires a documented restatement.
For year one, a defensible approach for Singapore-based manufacturers:
- Scope 1 stationary combustion: IPCC AR6 emission factors for each fuel type, with AR6 100-year GWP values for CH4 and N2O
- Scope 2 location-based: EMA grid emission factor for the relevant reporting year
- Scope 3 spend-based: EPA USEEIO v2.0 or Ecoinvent 3.x, with the version explicitly noted
Record which factor database version was used for each category. Factor databases are updated periodically, and the version you used in year one is what the base year calculation is built on.
Step 7: Build the Audit Trail as You Go
Year one is the only opportunity to build the audit trail properly from the start, because going back to reconstruct it retroactively is substantially harder. The audit trail for each emission entry requires: the source document (the invoice, meter export, or delivery receipt), the extracted activity data value and unit, the emission factor and its source and version, and the CO2e calculation. This chain needs to be preserved in a form that can be retrieved and inspected.
For a company assembling this in a spreadsheet, it means: keeping the source documents filed and referenced against their corresponding spreadsheet rows, noting the factor database and version in the calculation tab, and saving the final calculation file in a version-controlled location. This is more discipline than most spreadsheet-based processes apply, which is why the audit trail breaks down most often in year one when it was built without verification in mind.
What Year One Will Not Produce
A first-year emissions report is almost certainly incomplete relative to a mature GHG inventory. Some Scope 3 categories will be excluded pending better data. The base year numbers will be less accurate than subsequent years once data collection processes are established. Verifiers reviewing a first-year submission expect this, and it is better practice to disclose the limitations explicitly than to fill gaps with estimates that look more precise than they are.
The goal of year one is not a perfect calculation. It is a methodology, a base year, a data collection process that can be repeated, and documentation that survives the departure of the person who built it. Year two is faster, more complete, and more auditable if year one was built as infrastructure rather than as a one-time calculation.