The 4 Places First-Time GHG Inventories Go Wrong

If this is your company's first Scope 1 and Scope 2 inventory, you're going to get it wrong somewhere. That's not a knock, it's just how this works. The GHG Protocol runs hundreds of pages, the guidance documents assume familiarity you don't have yet, and most of the mistakes are invisible until someone who's built a lot of these points them out. Here are the four that show up most often, in roughly the order they tend to bite.

1. Fleet emissions: estimating instead of measuring

The instinct on mobile combustion (your vehicles, forklifts, backup generators, anything burning fuel that moves or could move) is to estimate: take total mileage, apply an average fuel economy figure, back into gallons burned. It's fast, and it's usually wrong enough to matter.

The defensible approach uses actual fuel purchase records (fuel card data or fleet fuel receipts) not modeled estimates. Two things trip people up here specifically. First, off-road and non-highway equipment gets forgotten almost every time: forklifts, gas-powered landscaping equipment, backup generators. None of it "feels" like a fleet, so it doesn't get pulled into the inventory, and it's Scope 1 the same as your trucks. Second, leased vehicles get misclassified, whether they belong in your inventory at all depends on which organizational boundary approach you're using (more on that in #4), and most first-time filers haven't actually decided that boundary before they start pulling fleet data, so the leased-vehicle question gets answered inconsistently across the inventory.

2. Refrigerants: the emissions source nobody thinks to look for

This is the one that gets missed entirely, not just measured badly. Refrigerant leaks (from HVAC systems, refrigeration units, chillers) are fugitive Scope 1 emissions, and because nothing is being combusted, most people building their first inventory don't think to include them at all. Facilities teams track refrigerant purchases and recharges for maintenance reasons, not emissions reasons, so the data usually exists, it's just never been pulled for this purpose.

Two errors show up even when someone does remember to include it. The GWP (global warming potential) multiplier varies enormously by refrigerant type: R-410A, R-134a, and R-32 aren't remotely close to each other, and using the wrong one doesn't just introduce a small error, it can be off by a full order of magnitude. And the more subtle mistake: the inventory should count refrigerant added or recharged during the reporting period (which reflects actual leakage), not the total refrigerant capacity sitting in all your systems. Those are very different numbers, and conflating them is one of the most common technical errors in a first inventory.

3. Purchased electricity: forgetting there are two required numbers, not one

Scope 2 isn't a single calculation, the GHG Protocol Scope 2 Guidance requires dual reporting under both the location-based method (using the average emissions factor for your regional grid) and the market-based method (reflecting any contractual instruments you hold, like RECs or a power purchase agreement). First-time filers frequently report only one, usually location-based, because it's the simpler calculation and nobody flagged that both are expected.

If you do hold renewable energy certificates or a PPA and want credit for it under market-based reporting, the documentation requirements are specific, unbundled RECs need certain tracked attributes to count, and "we buy some green power" isn't sufficient backup on its own. Get this wrong and the market-based number either overstates your position or gets flagged in review.

4. Organizational boundaries: the decision that should come first but usually comes last

Before any of the above matters, you need to have decided your consolidation approach (operational control, financial control, or equity share) because it determines what counts as yours at all. This is the boundary-setting step, and it's the one most frequently skipped or decided implicitly and inconsistently, which then contaminates everything built on top of it.

The place this actually bites: leased facilities and multi-tenant buildings. If you lease space in a building with shared HVAC or a shared boiler, your allocated share of that stationary combustion needs to be figured out (submetered, estimated by square footage, whatever's defensible) and this step gets skipped constantly because it's genuinely annoying to chase down. Recently acquired subsidiaries create the same problem: nobody's gone back and decided whether the acquisition falls inside your boundary for the full reporting year or only from the acquisition date forward.

None of these four are hard to fix once you know to look for them, they're hard to catch the first time through because nothing about the GHG Protocol tells you where people actually get stuck. That's really the gap: the guidance documents are complete, but they don't flag their own trip wires.

If you're building your first Scope 1 & 2 inventory and want a structured starting point that walks through data collection for exactly these categories, we've put together a free checklist. It's what I'd hand someone on day one if I were sitting across the table from them.