Scope 3 is usually the largest part of a contractor's footprint, and it is the part that tenders, lenders and customers increasingly ask about. It is also the part of corporate carbon data that researchers trust least. Two peer-reviewed studies show why.
What the research found
Reported value chains are incomplete. Lena Klaaßen and Christian Stoll at the Technical University of Munich studied 56 large technology companies (Klaaßen and Stoll, Nature Communications 12, 6149, 2021). They built a framework to harmonise Scope 3 reporting by correcting three problems: reporting inconsistency, incomplete boundaries and excluded activities. On their estimate, more than half of the sample's value-chain emissions were missing from self-reporting for 2019: about 751 megatonnes CO₂e against 360 reported, a gap of roughly 390 megatonnes. They also found that many companies gave different figures depending on where they reported, comparing annual reports with voluntary disclosures to CDP.
Scope 3 data is the least consistent. Timo Busch, Matthew Johnson and Thomas Pioch compared corporate carbon data across third-party data providers (Busch, Johnson and Pioch, Journal of Industrial Ecology 26(1), 350–363, 2022). Direct emissions agreed more closely than indirect emissions, and Scope 3 was the most inconsistent of all. Figures the companies had reported agreed more closely between providers than figures the providers had estimated.
Neither study is about construction. The pattern still applies to any organisation whose largest emissions sit with its suppliers: the less the figure is tied to a record, the more two people will disagree about it.
Habits that make a Scope 3 figure checkable
The problems these studies name are boundary, consistency and estimation. Each has a practical answer.
Write the boundary down. State which of the 15 Scope 3 categories you include and why the others are excluded or immaterial. A missing category is only a problem when nobody can tell that it is missing.
Report one figure everywhere. The tender answer, the SECR disclosure, the CDP response and the board pack should come from the same published snapshot. In MetricOra a published snapshot never changes; a recalculation creates a new version, and the dashboard shows when live data has moved away from the last one. See how publishing works.
Prefer records to estimates, and say which is which. Supplier data and physical quantities beat spend. Where spend is all you have, use a published factor for the supplier's industry at the factor's price year, and keep the selection reason. We explain the method in spend-based Scope 3 with factors you can source.
Keep the trail. An auditor should be able to go from a total to a category, to a record, to its evidence, factor and formula. The methodology page sets out the calculation rules MetricOra applies to every run.
Where to start
If your Scope 3 figure today is a single spend-based number, start by splitting it by category and adding industry codes to your largest suppliers. Then ask those suppliers for their own figures through a supplier data request. Every category that moves from estimate to record is one that will hold up when someone checks it.
Sources
- Klaaßen, L. and Stoll, C. (2021). Harmonizing corporate carbon footprints. Nature Communications, 12, 6149. doi:10.1038/s41467-021-26349-x
- Busch, T., Johnson, M. and Pioch, T. (2022). Corporate carbon performance data: Quo vadis? Journal of Industrial Ecology, 26(1), 350–363. doi:10.1111/jiec.13008
- GHG Protocol. Technical Guidance for Calculating Scope 3 Emissions.