GHG inventory vs verification: who does what?

The two words get used interchangeably in meetings, and they shouldn’t be: inventory (or GHG accounting) is the account your organization prepares; verification is an independent third party checking that the account is materially right. One you can do yourself; the other, by definition, you cannot. Mixing them up costs real money — either by buying assurance nobody asked for, or by discovering at disclosure time that somebody did.

The one-sentence difference

You (or your consultant) prepare an inventory under ISO 14064-1 or the GHG Protocol; an accredited third party verifies it under ISO 14064-3 and issues an opinion.

Side by side

	GHG inventory	Verification
Who does it	The organization itself, often with a consultant	Independent accredited verification body
Governing standard	ISO 14064-1, GHG Protocol	ISO 14064-3; ISAE 3410 for assurance engagements
Output	Inventory dataset + GHG report	Verification statement / assurance opinion
Timing	Annually, after year-end close	After the inventory is final, before disclosure
Independence	Not required	Required — your consultant cannot verify their own inventory
Cost driver	Internal time + data collection	Verifier days: scope, sites sampled, level of assurance

Two levels of assurance exist: limited (the verifier states nothing came to their attention suggesting material misstatement — cheaper, sample-based) and reasonable (a positive opinion that the inventory is materially correct — deeper testing, closer to a financial audit).

What verifiers actually look at

Knowing the checklist is the cheapest way to pass it:

• Boundary completeness — every entity and site accounted for, exclusions justified in writing.
• Data trail sampling — they pick line items and ask for the source document: the utility bill, the fuel invoice, the refrigerant service record.
• Emission factor appropriateness — source, vintage, geography of every factor; GWP set consistency.
• Recalculation — they recompute a sample and expect to land on your number.
• Base year and methodology consistency — changes explained and significance-tested.

When verification is mandatory

• Emissions trading / MRV schemes — installations under the EU ETS, China’s national ETS, and similar programs face mandatory annual third-party verification.
• CSRD — sustainability statements under the EU directive require limited assurance (with reasonable assurance signposted for later).
• California SB 253 — phased assurance on scope 1/2 disclosures for large companies doing business in California.
• Programs and customers — CDP scoring rewards verified data; large buyers increasingly require verified inventories from suppliers; Taiwan’s listed-company inventory mandate phases in verification deadlines.

If none of those apply, verification is optional — a credibility purchase, most valuable the first year a number goes public.

How to prepare an inventory that survives it

Verification is only expensive when the inventory wasn’t built to be checked. The difference is the evidence chain: every reported figure traceable to a source document, an activity-data value, a named emission factor, and a reproducible calculation. Concretely: keep the documents (bills, invoices, meter logs) attached to the data, not in someone’s inbox; record factor source and year on every line; document estimates and gaps as you make them, not retroactively. Build the account this way from day one — the step-by-step in our ISO 14064-1 inventory guide — and verification becomes a sampling exercise instead of an archaeology project.