Before an organization can set a meaningful emissions-reduction target, it needs to answer a basic question: how much are we actually emitting?
That sounds simple. In practice, building a credible greenhouse-gas baseline is one of the harder parts of climate reporting — not because the arithmetic is difficult, but because figuring out what to measure, where the data comes from, who owns it, which methods are being used, and whether the final number can be traced back to evidence takes real work.
For organizations preparing for IFRS S2 and broader sustainability disclosure, that distinction matters. An emissions inventory shouldn't just be a number that shows up in a report once a year — it should be a repeatable, documented, auditable process.
Start with the three scopes
The GHG Protocol splits an organization's emissions into three categories.
Scope 1 — direct emissions
Emissions from sources the organization owns or controls: diesel in company generators, gas in boilers or process equipment, fuel in company vehicles, flaring, refrigerant leakage. For many Nigerian organizations, diesel generators are the big one. The first challenge isn't calculating the emissions — it's establishing how much diesel was actually consumed, from reliable records rather than assumptions: purchase records, tank measurements, generator logs, whatever gives you something you can defend later.
Scope 2 — purchased energy
Indirect emissions from purchased energy — grid electricity, steam, heating, cooling. A facility running on a mix of grid power and diesel generation needs to understand both sources and how each contributes to the overall picture. Again, quality depends on the underlying data. Instead of "our facility uses approximately 10,000 litres of diesel a month," you want to be able to show where that figure came from — invoice, delivery record, storage, consumption, calculation. That's what creates an audit trail.
Scope 3 — the difficult one
Scope 3 covers everything else in the value chain: purchased goods and services, capital goods, transportation, business travel, employee commuting, waste, downstream logistics, use of sold products, end-of-life treatment, investments. Not every category matters for every organization — the real question is which ones are relevant and potentially significant for yours. Purchased raw materials and logistics might matter most for a manufacturer; financed emissions for a bank; use of sold products for an oil and gas company; purchased goods, food waste and travel for a hospitality business. Scope 3 shouldn't be treated as "the emissions we don't have data for" — it needs a structured look at the value chain.
Step 1 — Set your organizational boundary
Before collecting a single number, decide what the inventory actually covers: one facility, several, subsidiaries, joint ventures, leased assets, contractors, overseas operations? This matters most for organizations with complex structures, and it needs to be documented and applied consistently — otherwise you risk comparing two years of emissions calculated on two different boundaries without realizing it.
Step 2 — Build a source inventory
For every significant source, document the scope, the activity data, who owns it, and what evidence supports it.
| Emissions source | Scope | Activity data | Owner | Evidence |
|---|---|---|---|---|
| Diesel generators | Scope 1 | Litres consumed | Operations | Fuel records |
| Company vehicles | Scope 1 | Litres / fuel records | Fleet | Fuel records |
| Refrigerants | Scope 1 | Kg refrigerant added | Facilities | Maintenance records |
| Grid electricity | Scope 2 | kWh consumed | Facilities / Finance | Electricity bills |
| Purchased materials | Scope 3 | Quantity / spend | Procurement | Supplier records |
| Waste | Scope 3 | Tonnes by type | HSE / Facilities | Waste manifests |
| Business travel | Scope 3 | Distance / spend | Admin / HR | Travel records |
| Employee commuting | Scope 3 | Distance / mode | HR | Survey data |
The exact sources vary by organization. The principle doesn't: know what creates the emissions before you try to calculate them.
Step 3 — Collect activity data before calculating anything
This is where most organizations can improve. Don't start by grabbing an emission factor and multiplying it by a guess — start with the activity data itself: litres of diesel consumed, cubic metres of gas, kWh purchased, kilograms of refrigerant added or lost, passenger-kilometres travelled, tonnes of waste by type, quantities of materials purchased. Better activity data makes for a more defensible inventory, full stop.
Step 4 — Apply the right emission factors
Once you have activity data, converting it to emissions is straightforward in principle: activity data × emission factor = GHG emissions. What matters is documenting the factor used, its source, the applicable year, units, conversion assumptions, global warming potential values, and any estimation method involved. That documentation becomes essential the moment the inventory is reviewed or assured.
Step 5 — Be honest about missing data
Nobody's first inventory has perfect data, and that's not a reason to stop. Where primary data isn't available, use reasonable estimates or secondary data — and say so. "Supplier-specific data was unavailable, so an industry-average factor was applied" is a far stronger statement than presenting an estimate as if it were measured. The goal is to reduce uncertainty year over year: year one will have more estimates, year two should improve, year three further still. The baseline becomes a foundation you keep building on, not a one-off exercise.
Step 6 — Grade your Scope 3 data honestly
Scope 3 leans on information from suppliers, logistics providers and customers, which makes data quality especially important. A practical approach is to classify data by reliability — primary data obtained directly, supplier-specific secondary data, or industry-average proxy data used where nothing more specific exists. That gives management visibility not just into what the number is, but how much confidence to place in it.
Step 7 — Put controls around the inventory
This is what separates an emissions estimate from an actual emissions-management system. Who collects the data? Who reviews it? Who signs off on the methodology? What happens when a number shifts significantly from last year? Can the reported figure be traced back to source documentation, and could someone else reproduce the calculation? These are the same kinds of questions asked of financial data — increasingly for good reason, since sustainability information is moving into the same reporting environment.
Step 8 — Set a baseline year
Once the inventory is built, designate a baseline year to measure future performance against, and document the methodology behind it clearly — Scope 1, 2 and 3 totals plus how you got there. If the organization's structure changes materially, or better data becomes available later, you may need to recalculate the historical baseline. The goal is comparability: you want to be able to say emissions changed because actual emissions changed, not because the calculation method quietly shifted underneath the numbers.
Who should actually be in the room
A good starting point is a GHG inventory working group spanning HSE/Sustainability, Finance, Operations, Facilities, Procurement, Fleet, HR, Supply Chain and IT. Emissions data shouldn't sit exclusively with the sustainability team — Finance holds expenditure records, Procurement holds supplier data, Facilities holds electricity and fuel data, Fleet holds vehicle data, HR holds employee data, Operations holds production data. The quality of the final inventory depends on actually bringing those pieces together.
A readiness checklist
- Have we defined our organizational and operational boundaries?
- Have we identified relevant Scope 1 sources?
- Have we identified Scope 2 energy sources?
- Have we screened the relevant Scope 3 categories?
- Do we have documented activity data?
- Are emission factors sourced and documented?
- Are assumptions recorded?
- Are estimates clearly identified as estimates?
- Can calculations be traced back to evidence?
- Have responsibilities been assigned and reviewed?
- Can the methodology be repeated next year?
- Have limitations and uncertainties been documented?
A few unchecked boxes doesn't mean the baseline isn't usable — it means you know exactly where to improve it.
A credible emissions baseline isn't about producing an impressive number. It's about producing a number you can actually defend.
The sequence, in the end, looks something like this: identify sources, define boundaries, collect activity data, apply the right factors, calculate emissions, document assumptions, review, improve the data, establish the baseline, monitor performance. For Nigerian organizations preparing for IFRS S2, that work should start well before the reporting deadline becomes the trigger — because when reporting year arrives, the hard question won't be "what are our emissions?" It'll be "can we show how we got there?" That's the real difference between having an emissions figure and having a credible inventory.