How to Collect Scope 3 Data from Your Suppliers (Without Losing Them)

Your top 50 suppliers just got an email they didn't want. It's from your sustainability team, it asks for emissions data they've never measured, in a format they don't understand, with a deadline that assumes they have a carbon accounting system. They don't. Most of them don't even have a sustainability person.

This is the reality of how to collect scope 3 data from suppliers in Australia right now. ASRS Group 1 entities hit their second reporting year in 2026, which means Scope 3 is no longer deferred — it's mandatory. And for Group 2 entities (reporting from July 2026), the clock is already ticking on that one-year deferral. The data has to come from somewhere. The obvious source is your supply chain. But sending a 40-question survey to hundreds of suppliers and hoping for the best isn't a strategy. It's a way to get ghosted.

We've spent a lot of time thinking about this problem because, honestly, we're not sure anyone has cracked it at scale yet. The companies doing it well are doing it manually, carefully, one supplier at a time. The companies trying to do it at scale are drowning in incomplete responses and made-up numbers. This article is our honest take on what actually works — and what doesn't.

Start with Spend, Not with Surveys

The biggest mistake we see is treating all suppliers the same. A construction company might have 400 suppliers. Sending the same emissions questionnaire to the concrete supplier and the office stationery vendor is a waste of everyone's time.

The GHG Protocol's Corporate Value Chain Standard recommends prioritising data collection based on the significance of a supplier's contribution to your total Scope 3 footprint. In practice, the 80/20 rule applies almost perfectly here. Research from CDP and multiple consulting firms consistently shows that roughly 20% of suppliers account for about 80% of supply chain emissions. In some cases the concentration is even more extreme — one public-sector agency found that just 20 suppliers were responsible for 94% of their Scope 3 emissions.

So step one is a spend analysis. Pull your procurement data, sort by spend, and identify your top suppliers. For most Australian companies in construction, property, or manufacturing, you'll find that your top 20–30 suppliers by dollar value cover the vast majority of your purchased goods and services emissions (Scope 3 Category 1). That's where you put the effort.

For everyone else — the long tail of small suppliers — you use spend-based estimates. Australia actually has a decent dataset for this now. The Australian Spend-Based Emission Factor dataset (available through Zenodo and the IELab) provides emission factors in kilotonnes CO2-e per million AUD, broken down by ANZSIC industry classification. You take the procurement spend, classify it by ANZSIC code, multiply by the factor. It's not perfect. But it's defensible, it's consistent, and it means you're not chasing 300 small suppliers for data that won't materially change your numbers.

What to Actually Ask For (And What's Realistic)

Here's where the relationship damage happens. We've seen supplier questionnaires that ask for allocated Scope 1 and 2 emissions per product, cradle-to-gate lifecycle assessments, third-party verification certificates, and methodology documentation — all in the first email. For a mid-market Australian supplier that hasn't done any carbon accounting, that questionnaire goes straight to the "too hard" basket.

Be realistic about what your suppliers can provide. There's a hierarchy of data quality that the GHG Protocol recognises, and it's okay to accept data at different levels from different suppliers.

Supplier-specific data is the gold standard. This means the supplier has calculated their own Scope 1 and 2 emissions and can allocate a portion to your purchases. Very few Australian SME suppliers can do this today. Maybe 10–15% of your top suppliers, if you're lucky.

Activity data is the next best thing. This is physical data — kWh of electricity used, litres of diesel consumed, tonnes of waste generated — that you can convert to emissions using NGA Factors or other emission factor databases. Many suppliers can provide this even if they've never calculated an emission figure in their lives. Their energy bills have the data. Their fuel receipts have the data.

Spend-based estimates are the fallback. You use the economic value of what you purchased and apply an EEIO emission factor. The least accurate method, but the most practical for suppliers who can't or won't provide anything else.

The first time you engage a supplier, aim for activity data at minimum. Don't ask for emissions calculations they haven't done. Ask for information they already have: total electricity consumption at their facility, fuel purchases, major raw material inputs. You can do the emissions maths yourself. That's a much easier ask — and a much easier yes.

The Email Nobody Wants to Send (But Here's How to Write It)

Tone matters more than you think. We've seen supplier engagement emails that read like compliance demands — formal, legalistic, heavy on regulatory references. They work for companies that have leverage over their suppliers (big retailers, government procurement). They backfire for everyone else.

A better approach: lead with the relationship, explain the "why" briefly, and make the ask as specific and small as possible.

Something like this works better than a formal survey:

"Hi [Name], as part of our ASRS reporting obligations, we need to start reporting on supply chain emissions from this financial year. You're one of our top partners, so we'd like to include your actual data rather than using industry estimates — which tend to overstate emissions. Could you share your annual electricity consumption (kWh) and gas consumption (GJ) for your main facility? If you have fuel consumption figures for transport, that's helpful too. Happy to jump on a call if any of this is unclear."

Three things that email does right. First, it frames actual data as better for the supplier — because industry estimates almost always produce higher emission figures than reality. That's true, and it gives suppliers a reason to participate beyond "because you told us to." Second, it asks for data the supplier already has (utility bills). Third, it offers to help rather than just demanding.

Don't attach a 15-page questionnaire to the first email. Save the detailed survey for suppliers who've already agreed to engage. Treat it like any other business relationship — start small, build trust, escalate the ask over time.

Supplier-Specific vs Spend-Based: When Each Method Works

The GHG Protocol defines four calculation methods for Category 1 purchased goods and services. But in practice, Australian companies are choosing between two: supplier-specific and spend-based. The other two (hybrid and average-data) are variations that blend these approaches.

Here's our honest assessment of when each one makes sense.

Use supplier-specific data when the supplier is a top-20 partner by spend, when they're in an emissions-intensive sector (concrete, steel, chemicals, transport), when they have some degree of carbon maturity (they've done an emissions inventory or have ISO 14001 certification), and when you have enough purchasing power that they'll respond to you. If a supplier meets all four of those criteria, invest the effort. Send the questionnaire. Offer to help them calculate if needed. This is where the relationship-building pays off, because you'll need this data year after year.

Use spend-based estimates for the long tail. For the stationery supplier, the catering company, the IT consultant, the small subcontractor you used once for three weeks. Classifying this spend against ANZSIC codes and applying EEIO emission factors isn't ideal — the uncertainty ranges on spend-based factors can be plus or minus 50% — but it's the accepted approach under GHG Protocol guidance and it's what ASRS auditors will expect to see for immaterial suppliers.

The honest truth: most Australian companies reporting Scope 3 for the first time will use spend-based estimates for 80% or more of their suppliers and supplier-specific data for a handful. That's fine. The goal in year one is coverage, not precision. You refine over time.

We're still working out the best approach for mixed procurement categories where a single supplier provides both high-emission goods (say, concrete) and low-emission services (project management consulting) under one contract. Splitting the spend isn't always straightforward when invoices don't break it down that way.

When Suppliers Refuse (Or Just Go Silent)

It will happen. You'll send the email. You'll follow up. You'll follow up again. Nothing.

CDP's research on supply chain engagement identifies "dishearteningly low supplier response rates" as one of the four biggest challenges companies face when collecting Scope 3 data. Survey fatigue is real — your top suppliers are probably getting similar requests from five or six of their other customers. And many SME suppliers simply don't have anyone whose job it is to respond.

When a supplier won't or can't provide data, you have options. None of them are great. But they're all better than leaving a gap in your inventory.

Use spend-based estimates and flag them. This is the default. You calculate based on procurement spend and EEIO factors, document that you attempted supplier engagement, and note the data quality limitation. Under AASB S2, you're required to disclose the approach and assumptions used in your Scope 3 calculations. Being transparent about where you've used estimates versus primary data isn't a failure — it's what the standard expects.

Use industry-average data. If you know the physical quantity of goods purchased (tonnes of concrete, cubic metres of timber), you can apply average emission factors from lifecycle databases like AusLCI or Ecoinvent. This is more accurate than spend-based but requires you to have quantity data in your procurement records.

Escalate through procurement. If a supplier is strategically important and refuses to engage on emissions data, that's a conversation for your procurement team, not your sustainability team. When the ask comes from the person who controls the purchase order, the response rate improves. We're not suggesting you threaten suppliers — but making carbon data a standard part of supplier evaluation and onboarding changes the dynamic over time.

Group buy-in. Some industry groups are starting to coordinate supplier engagement. If you and three of your competitors all buy from the same concrete supplier, a joint request carries more weight than three separate questionnaires. The Property Council of Australia and some construction industry bodies have started exploring this approach, though it's early days.

The Safe Harbour and What It Means for Your Data Quality

Here's something that should lower your anxiety about getting Scope 3 "wrong" in year one. The modified liability regime under the ASRS legislation provides protection for Scope 3 disclosures through to financial years beginning before 1 January 2028. During this period, only ASIC can bring civil proceedings for misleading conduct related to Scope 3 statements — private litigants can't sue you over your Scope 3 numbers.

That doesn't mean accuracy doesn't matter. It means the government recognised that Scope 3 data quality is going to be rough in the early years and built in a transition period. ASIC's RG 280 guidance (released March 2025) makes clear that entities are expected to demonstrate genuine effort and reasonable processes, not perfection.

But — and this is important — Scope 1 and Scope 2 emissions are not protected statements. They carry full director liability from day one. So if your supplier engagement process is sloppy and that bleeds into your Scope 1 and 2 boundary assessment (it can, especially with operational control questions in joint ventures and outsourced operations), you've got a real problem. Get the governance right on your own operational emissions first, then tackle the supply chain.

Building the System, Not Just Filing the Report

The companies that will do this well aren't the ones with the best year-one numbers. They're the ones building a repeatable process.

That means setting up a supplier engagement calendar — not a once-a-year data dump, but a rolling process where you engage top suppliers early, give them time to collect data, provide support when they need it, and progressively improve data quality each year. It means integrating emissions data requests into your standard procurement workflows, so new suppliers get asked about carbon data during onboarding rather than as a panicked add-on six weeks before reporting deadline.

And it means accepting that your year-one Scope 3 number will be mostly estimates. 75% of total corporate emissions sit in Scope 3 on average, according to CDP analysis. For many Australian companies, that number is even higher. Pretending you can measure all of that precisely through supplier surveys in your first year of mandatory reporting isn't realistic. Building a system that gets 10% more accurate each year? That's the actual strategy.

At Carbonly, we're building tools to help with the parts of this that can be automated — spend-based calculations using Australian EEIO factors, tracking which suppliers have provided data and which are using estimates, maintaining the audit trail that ASRS assurance requirements demand. But the human work — the relationship-building, the phone calls, the explaining-what-kWh-means conversations — that can't be automated. And honestly, it shouldn't be.

Start with your top 20 suppliers by spend. Send the short email, not the long survey. Ask for data they already have. Accept estimates where you have to. Document everything. Improve next year.

That's it. That's the whole strategy.

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