Many businesses first hear about carbon reporting from a customer, not from a law. A large customer announces a net zero target, and a few months later a supplier questionnaire arrives asking for your emissions. This post explains why that happens, what the customer is likely to ask, and how to be ready before it lands.
How your emissions end up in your customer's target
Under the GHG Protocol, a company's footprint has three scopes. Scope 1 is its own fuel, Scope 2 is the electricity it buys, and Scope 3 is everything else in its value chain. Your Scope 1 and 2 are part of your customer's Scope 3. If you sell it goods or services, they fall in category 1, purchased goods and services; if you deliver for it, category 4; and so on.
For most companies that buy a lot, Scope 3 is the biggest part of the footprint, so a target that ignored it wouldn't be credible. Under the SBTi's near-term criteria, version 5.3.1, a company whose Scope 3 is 40% or more of its total must set Scope 3 targets that together cover at least 67% of its Scope 3 emissions. The customer can't cut those emissions by itself: it needs its suppliers to cut theirs.
Two ways the customer counts you
- An emissions target. The customer commits to cut its Scope 3 by a percentage. To show progress, it needs to measure what it buys, and the better its supplier data, the more real cuts show up.
- A supplier engagement target. The customer commits that suppliers making up a set share of its Scope 3 emissions, or of its spend, will have science-based targets within five years. Here it needs you to set a target, not just send a number. Our post on what to do when a customer asks you to set a science-based target covers that request in full.
Why your real figures matter to the customer
The GHG Protocol's Scope 3 guidance describes several ways to calculate purchased goods and services. The simplest, the spend-based method, multiplies what the customer spends with you by an average factor for your industry. It is quick, but it means the customer's figure for you only goes down if it spends less with you. A cut you make by changing your heating, your vans or your materials doesn't show.
The supplier-specific method uses figures from you instead. That is why customers ask: your data lets them replace an industry average with something that reflects what you actually do, and shows progress when you make real cuts. It also means a supplier with honest, lower figures can look better than the average for its industry. Our post on spend-based Scope 3 explains the method the customer probably started with.
What they typically ask
| Question | Why the customer asks |
|---|---|
| Your Scope 1 and 2 emissions, with the period and method | To replace a spend-based estimate with real data |
| Your emissions allocated to their account | So they can put their share of your footprint in their category 1 |
| Whether you have a reduction target, and whether it is science-based | To count you towards a supplier engagement target |
| Your Scope 3, or at least the main categories | Because your suppliers' emissions are in their value chain too |
| Renewable electricity, fleet plans or other actions | To show what is being done, not just measured |
| A response through CDP, EcoVadis or their own portal | To collect the same answers from hundreds of suppliers in one format |
Our guide to what to send when a customer asks for your carbon emissions covers each answer and how to allocate your emissions to one customer. For the platforms, see answering a CDP supply chain request and the EcoVadis carbon questions. If a request looks excessive, our post on what customers can reasonably ask helps you push back politely.
How to get ahead of it
- Watch your largest customers' announcements. A new net zero target, an SBTi validation or a sustainability report that mentions suppliers is the signal that supplier requests are coming.
- Measure Scope 1 and 2 now. A year of gas and electricity bills and vehicle fuel is enough. Our kWh to CO2e calculator gives a first figure with the government factors.
- Work out each big customer's share. Divide your emissions by revenue share, or by a physical measure if your products differ a lot, and keep the method the same each year.
- Set a target you can stand behind. A base year, a target year and a percentage. Only call it science-based if the SBTi has validated it.
- Write it up once. A Carbon Reduction Plan or a one-page summary answers most of the questions above, for every customer, in the same words.
- Talk to the customer. Ask what it needs and by when. Many customers would rather have honest Scope 1 and 2 figures this year and Scope 3 next year than nothing at all.
The SBTi's Corporate Net-Zero Standard V2.0 takes effect on 31 January 2027 and turns supplier engagement targets into broader supplier alignment targets, measuring the share of suppliers that are "in transition" or "net-zero aligned". The wording changes, but the direction doesn't: customers will keep asking suppliers for figures, targets and progress. If none of this is a legal duty for you, our guide to carbon reporting when the law doesn't require it sets out what level of reporting fits.
How Carbon Recycling helps
Start free: the kWh to CO2e calculator for your first Scope 1 and 2 figure, and the supplier questionnaire answer bank for model answers to the commonest customer questions, filled in from your own figures.
Carbon Recycling then works out Scope 1, location-based and market-based Scope 2, and Scope 3 by category with the government factors for each year, and its Carbon Reduction Plan sets your target and tracks each year against it, so every customer gets the same consistent answer. The 14-day free trial needs no card: you can add your data and see your reports, though printing and downloading them needs a plan. Plans start at £59 a month plus VAT (see pricing).