Weak Supplier Data Could Understate Scope 3 Emissions Threefold. Contracts Can Fix It

Scope 3 is usually the largest line in a corporate carbon footprint, and it is built mostly from other people's numbers. A new analysis suggests many of those numbers cannot carry the weight placed on them. When a company sets targets, prices carbon and chooses suppliers on estimates that may be a third of the real figure, the error does not stay in a spreadsheet. It flows into capital and sourcing decisions.

The Number Behind the Number

The EcoVadis and Kearney carbon analysis, reported by MH&L on September 21, draws on carbon performance data from more than 56,000 companies. Only 4 percent use primary supplier data to calculate their Scope 3 footprint. Most rely on industry averages or do not report the figure at all, and the report estimates that low-reliability inputs can understate a footprint by up to three times.

The consequences reach beyond reporting. According to coverage of the report, 77 percent of firms with verified data stayed on track with science-based targets, compared with 54 percent of those on lower-reliability data. Pierre-François Thaler, Co-CEO at EcoVadis, put the stakes plainly: "Companies are making capital and sourcing decisions on carbon numbers they can't actually trust."

The same pattern shows up in practitioner surveys. The MIT Sustainable Supply Chain Lab and the Council of Supply Chain Management Professionals surveyed 1,203 professionals in 97 countries, and ESG Dive reported that 70 percent named supplier data availability as the greatest obstacle to measuring Scope 3. MIT Sloan's summary adds that 66.1 percent of respondents track emissions in spreadsheets, 34.8 percent exclusively. That survey ran in 2025, so the EcoVadis findings suggest the problem has not eased.

Why Suppliers Are Not Handing Over the Data

The EcoVadis report finds that just 7 percent of companies engage suppliers on carbon issues, and only 12 percent of reporters share verified Scope 1 and 2 emissions data. A buyer cannot collect from suppliers that have none to give, and a supplier that has never been asked has little reason to build it.

The upside of that thin engagement is that the work is concentrated. The report finds the top 10 percent of emitting suppliers account for 95 percent of network emissions. A buyer does not need every vendor to submit a carbon footprint, only the few hundred that drive the total. Angela Hultberg, Global Head of Sustainability at Kearney, framed the payoff: "The businesses that invest in real data now will spend the next five years making better decisions than everyone is still guessing."

The financial case is explicit. The report estimates better data could save about $5 per metric ton of carbon across the typical supply chain by 2030. For an enterprise with 1 million tCO2e of operational emissions, that is roughly $135 million a year, which is the size of the blind spot when decisions rest on estimates.

The Request Has to Live in the Agreement

A data request sent by email is easy to ignore. The same request written into the supplier agreement is an obligation with a deadline, a format and a consequence. The EcoVadis coverage points to contractual requirements as one of the tools for driving supplier improvement, and the logic is straightforward: obligations that are not in the contract rarely survive the first busy quarter.

That puts procurement and legal teams at the center of a problem usually assigned to sustainability. The clauses matter, but so does knowing which agreements already contain them. A portfolio of thousands of supplier contracts, signed over a decade, is its own data gap, and closing it is a precondition for asking the right suppliers for the right numbers.

Companies moving from estimates to primary data are working through a practical list:

• Rank suppliers by emissions share. Start with the top 10 percent, since they account for most of the network total, and set data requirements there first.
• Write data obligations into the contract. Specify what must be reported, in which format, how often and with what verification, instead of relying on voluntary questionnaires.
• Audit the existing contract base. Identify which current agreements already carry emissions or ESG terms and which need amendment at the next renewal.
• Reward good data. Treat credible supplier reporting as a factor in awards and renewals so that disclosing becomes commercially worthwhile.
• Move off spreadsheets. Replace manual tracking with a system that holds supplier submissions, so a footprint can be traced to its source.
• Label what is still an estimate. Disclose which parts of Scope 3 rest on averages, so readers can judge the range rather than trust a single figure.

A footprint built on averages is a forecast, not a measurement, and the gap between the two can be large. The companies that close it first will not just report better. They will price, source and negotiate with numbers they can defend.