Why Scope 3 is fundamentally a data problem

Scope 1 and 2 are usually owned by facilities or energy managers. Scope 3 lives in procurement systems, travel bookings, expense claims, shipping records and supplier emails. The sustainability team rarely owns these systems.

This means the first task is not to calculate emissions. It is to locate the right data, understand how it is structured, and build a process to get it reliably every reporting cycle.

Spend-based emission factors are useful for a quick screening because they need only expenditure data. But they are not accurate enough for most reporting or target-setting purposes. They assume that every pound spent in a category produces the same emissions, which is rarely true.

A better approach is to build a category-level strategy: use spend-based factors where data is weak, activity-based factors where you have better information, and supplier-specific data where it is material and available.

The most resilient Scope 3 inventories are built as improvement programmes, not one-off calculations. Start with what you have, document the limitations, then systematically improve the highest-impact categories through supplier engagement, better procurement data and primary-data collection.