When an Assurer Questions Your Emissions Numbers

When your climate report is assured, the assurer works by sampling. They take figures from the report and ask you to trace each one back to its source, so a common early experience is a question you were not quite ready for: where did this Scope 2 number come from, and can you show the bill behind it. The number itself is usually fine. What catches first-time reporters out is that assurance tests whether you can demonstrate how each figure was built, and that is hard to reconstruct after the fact if the working was never kept alongside the number. This guide explains what a limited assurance review actually checks, why spreadsheet-based inventories struggle with it, and what it takes to make a figure traceable from the report back to the document it came from.

What the assurer is actually asking

From your first reporting year you need limited assurance over governance, your strategy risks and opportunities, and Scope 1 and 2 emissions. Limited assurance is a review rather than a full audit, and the word "limited" makes people relax. It shouldn't. Even in a review, the assurer samples figures and traces them: they pick a number, ask for the document behind it, and ask you to walk through how the document became the number. They're testing whether the figure can be relied on by someone who wasn't in the room when you built it.

Why a spreadsheet makes this hard

A spreadsheet can carry the arithmetic, and often the formulas too, but it rarely carries the provenance alongside each figure. The formula might show that megajoules were converted to gigajoules three columns over, without recording which invoice the reading came from, which edition of which factor was applied, or why a particular assumption was made. By the time the question comes, the source document is in a folder, the factor is on another tab, and the reasoning was a decision someone made in March. Each piece may exist somewhere, but nobody can start from the reported number and walk back to the bill without rebuilding the chain from memory. That's what "it wouldn't stand up to an audit" usually means: the maths may be fine, and still you could not show your work fast enough to prove it.

What a defensible number looks like

A figure survives assurance when it traces in one unbroken line. Start from the number in the report and you should be able to step back through each link without a gap:

If any link is missing, the figure cannot be assured. Keeping the trail also serves your own review, not only the assurer: when a number looks off, you want to see how it was built without opening five files.

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Common emissions errors assurers find

The same errors surface again and again once an assurer starts pulling threads.

The wrong state's electricity factor. Scope 2 factors differ sharply by grid, and a coal-heavy state's factor is several times a hydro-heavy state's. A single national factor, or the wrong state's, makes the number materially wrong before anyone opens the workbook.

A unit mismatch. Gas billed in megajoules on one invoice and gigajoules on another is a factor-of-1,000 error that sits quietly in a cell until someone traces it. A source-linked figure catches it. An eyeballed reference doesn't.

A number with no document. If a figure can't be traced back to the bill, the activity behind it and the factor applied, it won't survive assurance no matter how reasonable it seems.