How to collect supplier emissions data

Why is supplier emissions data so hard to collect?

Because the data sits in someone else's business, and most suppliers have never been asked for it before. Procurement teams send surveys, get a partial return, and fill the rest with spend-based proxy data. The replies that do arrive land in spreadsheets in different units, different reporting years and different boundaries, so they cannot be compared without manual work.

That is the real cost of collection: not the survey itself, but the chasing, the reformatting and the proxy data that ends up carrying most of the footprint anyway. Everything below is aimed at reducing all three.

Which suppliers should you ask for emissions data first?

Start with the suppliers that move the number: your largest spend lines and your most carbon-intensive categories, such as raw materials, manufacturing, freight and energy. Read the concentration off your own spend file rather than assuming a ratio, because it differs by industry and by how much you make in house.

Rank suppliers on two axes, spend and category intensity, and take the top group first. A short, targeted list is easier for your team to run and easier for a supplier to take seriously than a request sent to every vendor in the ledger. Add the next tier once the first cycle is running.

What emissions data should you ask a supplier for?

Ask for five things: total Scope 1 and Scope 2 emissions, the market-based or location-based basis of the Scope 2 figure, the reporting year, the organisational boundary the figure covers, and whether it has been third-party verified. Add one intensity metric, usually emissions per unit of revenue or per unit of production, so you can sense-check and scale it.

That is enough to replace a spend-based estimate with a supplier-specific one. Long questionnaires get partial answers, because the supplier either does not hold the fields or cannot tell what is being asked.

Ask for activity data (energy consumption, production volumes, fuel use) only from the suppliers mature enough to have it. Where a supplier has already reported to CDP, EcoVadis or in an annual report, take that instead of asking again. DitchCarbon reads existing responses: see upload a CDP response and upload an EcoVadis report.

How do you get suppliers to actually respond?

Tell them what you want, why you want it, and what you will do with it, in the first three lines of the request. Send a template with the five fields already labelled and one worked example filled in. Give a deadline that fits their reporting cycle rather than yours, and name a person they can reply to with a question.

Two things lift response rates more than any wording change. The first is asking for data the supplier already has, so the request is a lookup rather than a project. The second is giving something back: their figure alongside their sector, or the calculation they can reuse the next time a customer asks. Both point the same way: a prepopulated request, where the figures are already filled in and the supplier only has to check them, gets a higher response rate than a cold survey.

That reuse is the point. The supplier answering you is also being asked by their other customers, and often by an investor, and they are usually somebody's procurement team too. A profile they can answer once and reuse is worth more to them than another completed spreadsheet, which is why we built the survey responder and claim your profile for the other side of the request.

What is the best way to collect supplier emissions data at scale?

Spreadsheets and survey forms work for twenty suppliers and break at two hundred. The work that breaks is not the sending, it is the tracking, the reminders, the version control and the manual normalising of every reply into one comparable set. Past a few hundred suppliers, most teams move to a platform that holds the data and the follow-up in one place.

DitchCarbon provides verified emissions data for over 2 million organisations, so procurement, sustainability and finance teams can measure and act on supply chain and portfolio emissions from one source. In practice that inverts the order of work: you start with a figure for most of your supplier list already in place, then spend your engagement time on the suppliers where a better number would change a decision. See how it works.

What do you do about the suppliers who never reply?

You estimate, you label the estimate, and you keep the gap visible. The GHG Protocol Scope 3 Standard sets out four calculation methods for Category 1, purchased goods and services: supplier-specific, hybrid, average-data and spend-based. Mixing them across one category is expected, as long as you record which method sits behind each line.

Document the assumption next to the figure: the method used, the factor set (CEDA, Ecoinvent, DEFRA, EPA or similar), the year and the reason primary data was not available. An auditor will accept an estimate with provenance. An auditor will question a footprint where the method cannot be traced.

Then treat the gap as the work list. Coverage gaps shown, not hidden, is the standard to hold yourself to, and each cycle should move suppliers out of the estimated column rather than restate the same total.

How do you standardise and validate supplier emissions data?

Normalise four fields before anything else: units (tCO2e, not tonnes of CO2 or kg), reporting year, Scope 2 basis, and the legal entity the figure covers. Then run three checks: intensity against the supplier's sector, this year against last year for the same supplier, and Scope 1 plus Scope 2 against the revenue you have on file.

Entity matching is where most supplier datasets quietly go wrong. The name on a purchase order is a trading name, a subsidiary or a misspelling, so the same supplier appears three times and one figure gets counted twice. Match on identifiers rather than strings. DitchCarbon runs entity resolution against DUNS, LEI and ISIN identifiers, and every figure carries its source and change history, so a line in the report can be traced back to the document it came from.

Align the result to the GHG Protocol Scope 3 Standard categories at the point of aggregation, not afterwards.

Will supplier emissions data stand up to an auditor?

It will if three things are true: every figure names its source, every estimate names its method, and the changes between one version and the next are recorded. Auditors do not object to estimates. They object to numbers whose origin nobody can reconstruct, which is what a rebuilt spreadsheet produces.

That is the difference between audit-ready and simply finished. DitchCarbon's calculator is verified to ISO 14064-3, limited assurance, by UL Solutions, renewed annually, and the emission factor methodology was independently assessed by Globus Thenken in August 2025. Both documents are downloadable from the trust centre, so your auditor can read them rather than take our word for it. DitchCarbon data has also been used in emissions reports that were subsequently assured by ten different third-party assurance providers, including Big Four firms.

How often should you refresh supplier emissions data?

More often than once a year. An annual collection round tied to the reporting deadline gives you one snapshot, already months old by the time it is published, and no way to tell whether an engagement programme is working. Quarterly refresh is what makes a reduction target trackable.

Continuous refresh with documented sources removes the choice between currency and effort, because the base layer updates without another round of requests. Your team's time then goes on the exceptions: new suppliers, changed entities, and the figures that moved enough to need a look.

How do you ask suppliers for data without damaging the relationship?

Ask once, ask for less, and never ask for something you could look up. Suppliers receive the same request from many customers in slightly different formats, and each one costs them unpaid hours. The request that gets answered willingly is the one that is short, specific about its use, and accepts data the supplier has already prepared for somebody else.

Give the relationship something back. A supplier that can see its own figure, its sector comparison and the two changes that would move it has a reason to keep the profile current. A supplier that only ever receives a spreadsheet has a reason to deprioritise you next year. Supplier engagement covers how teams run this at scale.

What do you do once you have supplier emissions data?

Use it to choose. A complete supplier footprint tells you which categories carry the emissions, which suppliers inside them have a credible target, and where a sourcing decision would change the number. That is the point at which measurement becomes reduction.

Set the baseline first, then the target, then track at supplier, category and group level so progress is attributable rather than aggregate. Our guide on how to reduce Scope 3 emissions takes it from there.