Customer Sent You a Sustainability Questionnaire?...

A PDF arrives by email. Subject line: "Annual Sustainability Data Request, response required by [date]." It's from a customer who buys enough from you that you can't ignore it. Forty-something questions. Half of them assume you have a carbon ledger you don't have. The deadline is four weeks away.

This is happening to thousands of Australian suppliers right now. Every Group 1 ASRS reporter is disclosing Scope 3 this year. Group 2 starts FY26-27. The big retailers, the major banks, the iron ore majors, the construction head contractors all need supplier data to close out their own disclosure obligations. So the questionnaires get pushed down the chain.

Here's the practical response framework.

What's actually in the questionnaire

Once you've responded to one, you've seen the pattern. Around 90% of supplier sustainability questionnaires in Australia ask for eight things:

Scope 1 and 2 totals for your most recent reporting year, in tCO2-e.
Scope 3 emissions attributable to the customer: your share of their value chain, not your entire Scope 3.
Emission factor sources and methodology: what database, what GWP set, what standard.
Boundary definition: operational control, financial control, or equity share.
Data quality: measured, calculated, or estimated, and ideally a PCAF-style tier (1 = supplier-reported and assured, 5 = industry average spend-based).
Reduction targets: baseline year, target year, scope coverage, SBTi status.
Renewable energy claims: percentage, contractual instruments, vintage year.
Verification status: limited assurance, reasonable assurance, or unassured.

If the questionnaire is the CDP Supply Chain version, expect closer to sixty questions and a scoring rubric. CDP reported almost 45,000 suppliers were requested to disclose in 2025 through their Supply Chain program, by 270 corporate buyers. The CDP corporate questionnaire for 2026 adds ocean disclosures and expanded forest scoring, with responses due between June and October.

If it's a customer-built questionnaire, the questions are usually a simplified version of the same standard. Coles, for example, has publicly committed to working with 75% of suppliers by spend to set science-based targets by June 2027 under its Together to Zero program. Woolworths Group is targeting a 55% reduction in Scope 3 energy and industrial emissions by FY33 from a FY23 baseline. Neither of those targets is achievable without supplier data.

Two response paths, divided by how much they buy from you

How much effort the response deserves depends on the size of the commercial relationship.

Tier 1 supplier (the customer is one of your top 20 by revenue). Full response. Real data. Methodology documented. Source documents kept. The customer's auditor may pull your numbers back into a sample test, and your response will be referenced in their AASB S2 disclosure or CDP submission. Treat it as you would treat a financial audit response.

Long-tail supplier (you're a small share of their spend). An industry benchmark or a spend-based estimate is acceptable, provided you document the approach honestly. The customer is rolling up thousands of suppliers and will apply spend-based defaults to anyone who doesn't respond at all. Sending a documented spend-based number is better than sending nothing, and substantially better than sending an inflated guess.

Either way, the rule is the same: only write down what you can defend.

What you should never do

The supplier is often the weakest link in a greenwashing chain. The customer publishes your number. If the number is wrong, the customer is exposed and you are the source. Bad outcome for both.

Don't claim "carbon neutral" without offset retirement records. Climate Active certification is the only widely-recognised pathway in Australia, and the ACCC has been actively scrutinising standalone neutrality claims since the Mercer and Vanguard penalties.

Don't state a renewable energy percentage without a contractual instrument backing it. If your retailer sold you GreenPower, you have a certificate. If you have rooftop solar but no LGCs, you have on-site generation, not market-based renewable claims.

Don't round up an estimate the customer will publish. A 15% overstatement of your Scope 1 looks small in your spreadsheet and looks like a misrepresentation in their disclosure.

Don't reuse last year's number without checking it. NGA Factors update annually, and the VIC grid factor moved from 0.77 to 0.78 between the 2024 and 2025 editions. Different bills, same usage, different number.

Don't sign anything attesting to assurance that hasn't happened. "Unassured" is a legitimate answer. "Limited assurance" without an actual assurance report is not.

Don't quote a number you can't trace to a source document. If the auditor calls in six months, you need to point at an electricity bill, a fuel invoice, or a refrigerant log.

The methodology paragraph

This is the most-asked question and the most-mishandled. The questionnaire usually has a single text box labelled "describe your methodology." Most suppliers leave it blank or paste in a vague sentence. Both signal the data isn't credible.

Here's the structure that works. Five points, in plain language:

Boundary used. Operational control is the default under the GHG Protocol Corporate Standard and matches how NGER treats reporting boundaries. State it.
Emission factor source. For Australian operations, "NGA Factors 2025" answers this for Scope 1 fuels and Scope 2 electricity. For imported inputs, name the database (DEFRA, US EPA, ecoinvent).
GWP set. AR5 if you're aligning to NGER, AR6 if the customer is asking for AASB S2 alignment. Both are legitimate, and the AASB issued jurisdictional relief in late 2025 allowing NGER reporters to keep using AR5 for the NGER-covered portion of their AASB S2 disclosure.
Allocation method. Only relevant if you're calculating a customer-specific share. Revenue, volume, or activity-based. State which.
Data quality tier. PCAF uses a 1-to-5 scale where 1 is supplier-reported and verified, 5 is economic-activity estimation. The customer doesn't need you to use the exact PCAF rubric, but stating the equivalent ("metered electricity, supplier invoice fuel, industry-average for purchased materials") gives them what they need.

A paragraph along these lines will satisfy 90% of questionnaire methodology questions. Save it. Reuse it. Update the factor year annually.

How to figure out the customer's share of your Scope 1 and 2

This is the question most suppliers fudge. The customer wants to know "what portion of your operational emissions should I count in my Scope 3 Category 1?"

There are three honest options:

Revenue-based allocation. Customer revenue divided by total revenue, multiplied by your Scope 1+2. Defensible as a default. Easy to calculate. Used by most suppliers who don't have product-level cost accounting.

Volume-based allocation. Customer kilograms or units divided by total kilograms or units, multiplied by your Scope 1+2. Better for manufacturers where emissions track production volume more closely than revenue.

Activity-based allocation. Customer-attributable production hours, line time, kWh of process electricity, or fuel consumed divided by the total. The most accurate option for industrial suppliers with metered production data. The hardest to assemble without a system.

Pick one. Document the choice in the response. The customer will not ask which method you used until their auditor asks them, and at that point the answer needs to already be in writing.

The GHG Protocol Scope 3 Standard, Category 1 describes four calculation methods in detail (supplier-specific, hybrid, average-data, spend-based). The supplier-specific method, where the supplier provides primary data with allocation, is the highest-quality pathway and the one that earns the customer credit in their own disclosure.

Your Scope 3 in their Scope 3

Most suppliers get this wrong by either over-disclosing or under-disclosing.

The customer typically wants your Scope 1, your Scope 2, and the upstream portion of your Scope 3 that flows through to them as a physical product (your Scope 3 Category 1 emissions, allocated to their share). They generally do not want your business travel, your employee commuting, or your end-of-life waste.

If the questionnaire asks for "full Scope 3," ask for clarification before sending fifteen categories of data the customer doesn't actually need. Over-disclosing inflates the customer's Category 1 figure and increases the chance of double-counting elsewhere in their value chain.

The recurring question: do we have to respond?

Practically, no. Legally, almost never (unless your supply agreement has a sustainability clause, which more of them now do). Commercially, the picture is different.

Coles has publicly stated the 75%-by-spend supplier target. Woolworths' Responsible Sourcing Program makes supplier self-assessment a condition of trading. The big four banks are running green-loan and sustainability-linked-loan products that tie pricing to disclosed emissions data. BHP and Rio Tinto's contractor prequalification packs include emissions reporting capability questions. Suppliers who can respond credibly are winning longer contracts. Suppliers who can't are quietly being deprioritised.

You don't have to respond. The customer doesn't have to renew.

What the customer will do with your response

It goes into their AASB S2 Scope 3 disclosure (paragraph 29(c) of AASB S2 requires reporting by Scope 3 category). It feeds their CDP submission. It populates their internal supplier sustainability scorecard. It sometimes drives procurement decisions, particularly for contracts being put out to tender against suppliers who can also show third-party assurance.

The customer's auditor, under ASSA 5010, will sample-test their Scope 3 number once reasonable assurance kicks in. Your data may be in that sample. If it is, the auditor will ask the customer for the source, and the customer will ask you. Knowing what you sent and how you calculated it matters.

A template paragraph for the response cover note

This generic structure works for most questionnaires. Adapt it to your numbers:

[Supplier name] calculates emissions under the GHG Protocol Corporate Standard, using the operational control boundary. Scope 1 and 2 emissions for the financial year ending [date] were [X] tCO2-e and [Y] tCO2-e respectively, calculated using NGA Factors 2025 with AR5 global warming potentials. Emissions attributable to [Customer name] are estimated at [Z] tCO2-e, calculated using revenue-based allocation ([customer revenue] / [total revenue] = [%] of operational footprint). Activity data is sourced from electricity invoices, fuel supplier statements, and refrigerant service records. Underlying methodology, data quality notes, and source documents are available on request to your assurance provider. This response is unassured.

That paragraph answers the boundary, factor source, GWP, allocation method, data quality, and verification status. Six questions, one paragraph. It's also defensible if it ends up in the customer's AASB S2 working papers.

Responding once is a project. Responding to 20 a year is a system.

The first questionnaire is usually a scramble. Operations digs out the electricity bills. Finance pulls the AP file for fuel invoices. Someone with a calculator multiplies kWh by the state grid factor. A draft response gets emailed around for sign-off the night before the deadline.

The second one is faster but still painful. By the fifth, the same pattern of questions starts hitting different people in the business, all asking for the same underlying numbers in different formats. The CDP version wants tabular data with category splits. The Woolworths version wants narrative answers. The bank's green-loan covenant wants a sub-set with assurance.

What works is a single emissions ledger that holds the underlying data once. Source documents linked to each entry. Methodology documented in one place. The ability to slice by customer, product line, or facility, because the next questionnaire will ask for the slice differently.

That's the architecture Carbonly is built for. The same source documents that feed your NGER report (if you're a reporter) and your AASB S2 disclosure (if you're caught by the threshold) feed your customer questionnaire responses. Eight file formats in, structured emissions data out, with the source invoice still attached to every number for the day the customer's auditor asks. JV consolidation handles cases where you share a facility with a customer or partner. Carbonly's outputs produce data extracts that feed CDP submissions, AASB S2 disclosures, and customer-specific response templates without recalculating from scratch each time.

If you're getting more than one questionnaire a year, you have a system problem, not a content problem.

What to do this week

If the questionnaire deadline is close, focus on three things. Get your electricity consumption confirmed against the bills (not estimated). Get your fuel volumes confirmed against supplier statements (not the fuel card spend total). Document the allocation method you used to attribute the customer's share.

If you're early on the deadline, set up the response template now and use it for every future questionnaire. The methodology paragraph above is the asset you'll reuse most.

Either way: write down only what you can defend in twelve months.

Contact us at hello@carbonly.ai if you want help building the response infrastructure once and using it for the next twenty questionnaires.

Customer Sent You a Sustainability Questionnaire? The Australian Supplier Playbook