How to baseline Scope 3 without losing six months
Scope 3 is where most ESG programmes stall. A pragmatic baseline beats a perfect one — here is the order to attack it in.
Start with the screening, not the inventory
Before measuring anything, classify your spend or activity across the 15 GHG Protocol Scope 3 categories. Most companies find 80%+ of emissions cluster in 3-4 categories: purchased goods and services, business travel, employee commuting, and use of sold products.
Use spend-based factors for the long tail
- For categories below 5% of estimated total, spend-based factors (e.g. EXIOBASE, USEEIO) give defensible numbers without supplier surveys.
- Document the factor source and version per category. Auditors care more about traceability than precision in year one.
Upgrade your top categories to activity data
Once you know the top categories, replace spend-based with activity-based: actual km flown for business travel, actual kg of purchased steel, actual kWh used by sold products. This is where supplier engagement starts.
Pick a baseline year you can defend
Avoid 2020 and 2021 — COVID distortions make trajectories meaningless. Pick the most recent year with complete data. SBTi accepts any year with full inventory.
Set the recalculation policy now
Decide upfront how you will treat M&A, divestments, factor updates and category re-screening. A common rule: recalculate the baseline if structural changes shift it by >5%.
Tooling matters more than you think
Spreadsheets work in year one. By year three, with multiple suppliers, factor updates and assurance trails, they break down. Move to a tool with per-row source, version-pinned factors and year-over-year comparatives.
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