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Primary vs spend-based emissions: what the difference actually costs you
Most Category 1 inventories start the same way: a line of spend, multiplied by a sector average. It is fast, and it cannot tell two suppliers apart. Cut spend with a supplier and the number improves. Nothing else moves it, whatever that supplier actually does. Primary emissions data, calculated from what an organisation has actually disclosed, is the alternative, and it costs less than most procurement and sustainability teams assume.
Spend-based describes the input, not the quality of the answer
The variable that decides whether a number can be acted on is the emission factor, not the spend file behind it. The same invoice multiplied by a sector average produces a figure that only tracks procurement's decisions. The same invoice multiplied by that organisation's own factor produces a figure that moves when the supplier reports a reduction. The GHG Protocol calls the sector-average version spend-based. Once the factor comes from what that organisation has actually published, it is a different calculation wearing the same input.
The rung most teams don't know is available
There are four ways a Category 1 line gets calculated, and they don't cost the same:
Costs a spend file. Costs the supplier nothing. Never moves when they cut emissions.
Costs nothing extra, where that organisation has already published a figure. Moves when they cut emissions. This is primary emissions data, in spend-based form.
Real effort to gather consumption data, often from the supplier. Separates two suppliers doing the same thing differently.
Allocating spend to named products, item by item, against a footprint the supplier has published for that item.
The second rung is the one worth knowing about. It converts an unactionable line into an actionable one, with no additional burden on procurement and none on a supplier that has already disclosed.
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