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4 Ways to Improve Scope 3 Data Quality Over Time
Supplier emissions data will always be incomplete. The organizations making real progress treat Scope 3 as a system that gets stronger with every reporting cycle.
Few areas of environmental reporting carry as much uncertainty as Scope 3. Companies are asked to account for emissions across purchased goods, transportation, product use and other activities in a value chain they don’t control. Much of the information comes from suppliers who measure it differently, report it on different timelines, or don’t track it at all.
The scale of the gap is significant. The 2026 Carbon Action Report from EcoVadis and Kearney drew on data from more than 56,000 companies. It found that only about 40% of companies report Scope 3 emissions at all, and just 4% use primary supplier data to calculate them. The research also suggests that companies relying on less reliable data could underestimate their supply chain emissions by as much as three times.
None of this means Scope 3 emissions reporting is futile. It means the goal needs to be realistic. Complete, perfectly accurate supplier data is unlikely to be achievable for most organizations. A more useful objective is transparency about where the data comes from and steady improvement over time. The GHG Protocol’s guidance on filling data gaps supports that view. It treats estimates and proxies as legitimate starting points that companies should refine as better information becomes available.
The following four practices can help environmental and sustainability teams make that improvement deliberate rather than accidental.
1. Focus first on the biggest data gaps
Not every data point deserves the same level of effort. A Scope 3 inventory can involve thousands of suppliers and line items. Trying to improve all of them at once makes it difficult to achieve meaningful progress.
Start by identifying the suppliers, categories and activities that contribute most to total emissions. Take a commercial furniture manufacturer for example. Hardwood, steel frames, foam and upholstery fabric may account for the bulk of its purchased-goods emissions, with outbound freight close behind. These are the areas where more specific information will have the greatest impact on overall accuracy.
Within those priority areas, teams can take several concrete steps. They can request primary data from key suppliers, replace spend-based estimates with calculations based on physical quantities, such as kilograms of steel or cubic meters of timber, or separate a high-impact material from a broad category average.
How the data will be used should also guide priorities. A gap that only affects disclosure completeness is less urgent than one that could influence a sourcing decision, product redesign or reduction target. For low-impact categories, a reasonable estimate may remain the right choice for years.
2. Be clear about where the numbers come from
Two emissions figures can look identical in a report and carry very different levels of confidence. Consider three versions of the same number. One was calculated by a supplier from its own metered energy use. Another was derived from purchase quantities and a published emission factor. A third was estimated from spend and an industry average. Each reflects a different degree of certainty.
Every figure in the inventory should carry a record of its source: supplier-specific data, activity data, a spend-based estimate or an industry average. That record shows how much of the inventory rests on primary information and how much on approximation. It also points directly to where improvement efforts should go.
Source tracking doesn’t mean supplier data should be accepted at face value. Primary data can be incomplete, can cover a different reporting boundary, or can use methods that don’t align with the company’s own approach. Knowing a figure came from a supplier is the starting point for review, not the end of it.
3. Document assumptions and calculation methods
A Scope 3 total is only as defensible as the methods behind it. The same purchase can produce different emissions results depending on whether the calculation uses spend, physical quantities or supplier-specific factors. Emission factors can also vary by source, region and year.
For every category, teams should record the calculation method, the emission factors and their versions, and any assumptions made to fill gaps. Assumptions might cover a supplier’s energy mix, an average shipping distance or the share of recycled content in a material. This documentation serves several purposes. It allows internal and external reviewers to follow the logic. It helps explain year-over-year changes. And it makes clear what should be revisited when better data becomes available.
Documentation also exposes the limits of certain methods. Spend-based calculations, for example, are tied to price. A furniture manufacturer that switches to a pricier low-carbon steel for its frames could see its calculated emissions rise, even though its actual emissions have fallen. Spend-based methods remain useful for screening and for categories where nothing better exists. Clear documentation helps ensure these estimates aren’t mistaken for precise measurements.
4. Build on each reporting cycle instead of starting over
One of the clearest signs of a maturing Scope 3 program is how much of the work carries forward from year to year. If every cycle requires teams to chase the same suppliers, revisit old assumptions and figure out who is responsible for what, the program isn’t improving. It’s repeating.
At the end of each cycle, teams should note where data quality improved, where gaps remain and what changed. The furniture manufacturer, for instance, might record that its steel emissions calculations are now supported by supplier data. It might note that foam still relies on industry averages, and freight emissions shifted because of a new distribution center. That record becomes the starting point for the next inventory.
Clear ownership is central to this continuity. Scope 3 data spans procurement, operations, finance and sustainability, so responsibility rarely sits with one person. Clear assignments make the process repeatable and prevent institutional knowledge from disappearing when people change roles. This means assigning responsibility for supplier requests, reviewing methodologies and supporting evidence, and determining when estimates need to be replaced.
From reporting to decisions
As data quality improves, Scope 3 data becomes valuable well beyond the annual report. Teams with a clearer view of their largest emissions sources and the reliability of their data can set more credible reduction targets. They can engage with suppliers to identify specific improvement opportunities and consider emissions alongside cost and risk in sourcing and logistics decisions.
Scope 3 reporting will continue to involve estimates, particularly for emissions deep in the value chain. The key is knowing where those estimates are used, documenting how they were calculated and prioritizing improvements where they will have the greatest impact. Over time, this makes each reporting cycle more manageable and gives companies more reliable emissions data to inform business decisions.
About the Author
Chris Winchurch is General Manager of Novisto Carbon, following Novisto’s 2026 acquisition of Minimum. He leads strategy and execution for Novisto’s carbon offering.
