Scope 3: The Emissions You're Responsible for Communicating, Even If You Can't Count Them Yet

A few years ago, Scope 3 was a phrase you only heard from sustainability consultants and the people writing large corporate climate reports. Now it arrives in your inbox as a supplier questionnaire from your biggest customer, with a deadline and a tone that suggests your contract might depend on the answer.

That is the shift most smaller businesses haven't quite caught up with. Scope 3 emissions used to be someone else's problem. They are now a communications problem you own, whether or not you have measured a single tonne of them.

This piece isn't a technical explainer. There are plenty of those, and most of them will tell you more than you need to know about emission factors and spend-based methodologies. The harder question, and the one almost nobody is answering for smaller businesses, is what you're actually expected to say about Scope 3 when you can't yet measure it properly. That's where the real risk sits.

Scope 3 is the Emissions You Don't Control but Still Have to Talk About

The quick version, because you need it to follow the rest.

Greenhouse gas emissions get split into three scopes. Scope 1 is what you burn directly, the gas boiler and the company vans. Scope 2 is the energy you buy, mainly electricity. Scope 3 is everything else across your value chain. The emissions from the products you buy, the goods you sell, the business travel, the waste, the way customers use what you make. The GHG Protocol, which is the standard almost everyone works from, breaks Scope 3 into fifteen categories.

Here is the part that matters. For most businesses, Scope 3 is not a footnote. It is the majority of the footprint, often the overwhelming majority. And it is also the least precise number you will ever report, because you are estimating activity that happens inside other companies you don't control.

That combination, biggest and least certain, is exactly what makes Scope 3 communications difficult. You are being asked to say something credible about the largest part of your impact using the weakest data you have.

Why SMEs are Suddenly Being Asked

You are not imagining the pressure. It is real, and it is structural.

The reason it lands on smaller businesses is that Scope 3 flows downhill. A large company's Scope 3 is, in large part, your Scope 1 and 2. When that company commits to a science-based target, it inherits a problem it can only solve by leaning on its suppliers. So it asks you for data.

The Science Based Targets initiative makes this explicit. If a company's Scope 3 emissions are more than 40% of its total footprint, which for most is the case, it has to set Scope 3 targets, and its near-term target must cover two-thirds of those emissions. There is also a specific supplier engagement target that commits a company to getting its suppliers to set their own targets within five years. If you supply a business that has signed up to this, you are the engagement.

The regulatory layer reinforces it. IFRS S2, the ISSB's global climate disclosure standard, requires Scope 3 reporting where it is material, which for most companies it is. The EU's CSRD pulls value chain emissions into scope. California's SB 253 requires large companies doing business in the state to disclose Scope 3. None of these rules target your small business directly. They don't need to. They reach you through the customer who has to comply and needs your numbers to do it.

So the request you're getting is not your customer being difficult. It is your customer passing on an obligation they cannot meet alone. Understanding that changes how you respond to it.

The Two Ways Scope 3 Communication Goes Wrong

When the pressure arrives, businesses tend to fail in one of two directions. Both are avoidable, and both are more common than they should be.

Saying nothing, and hoping the silence reads as caution

The first failure is to publish nothing on Scope 3 at all. You report your Scope 1 and 2 figures, which are clean and defensible, and you stay quiet on the rest.

The problem is that selective disclosure is now one of the most recognised forms of greenwashing, and it is increasingly the first thing a sceptical reader looks for. A business that publishes detailed Scope 1 and 2 data and says nothing about Scope 3 is, to an informed audience, almost certainly hiding its largest source of emissions. The silence doesn't read as caution. It reads as avoidance.

This matters more now that audiences, regulators and NGOs are reading claims more closely than they were even two years ago. The gap in your reporting is no longer invisible. It is often the most visible thing about it.

Claiming precision you don't have

The second failure is the opposite. You produce a Scope 3 number, usually built from industry-average emission factors, and you present it as if it were measured. You put it in a headline. You compare it year on year and call a small movement a reduction.

The trouble with industry averages is that they are estimates designed to give you a broad picture, not a precise one. Build a claim on top of an estimate and present it as fact, and you have manufactured exactly the kind of overstatement that regulators are now fining companies for. In the UK, the CMA's strengthened powers under the Digital Markets, Competition and Consumers Act 2024 allow fines of up to 10% of global turnover for misleading consumers. The point is not that an SME will be the headline case. The point is that the same standard of evidence now applies regardless of size, and a number you can't stand behind is a liability whether or not anyone has counted your turnover.

Both failures come from the same mistake. Treating Scope 3 as a number to be defended, rather than a process to be described honestly.

What You Can Honestly Say, and What You Can't Yet

This is the part that actually helps. There is an honest middle ground between silence and overstatement, and it is more credible than either.

You can say what you have measured, and be specific about it. "We've measured our Scope 1 and 2 emissions and our business travel and waste. We're working on the rest." That is a true statement and a stronger one than a complete-looking number you can't defend.

You can label estimates as estimates. If your Scope 3 figure is built on industry averages, say so. "This is an early estimate based on industry data, not supplier-specific figures." Naming the method is not a weakness. It tells a knowledgeable reader you understand the difference, which is itself a credibility signal.

You can describe the direction of travel without claiming the destination. "We know purchased goods are our biggest source of emissions, and that's where we're focusing." You don't need a precise figure to say honestly where the weight sits.

What you can't yet do, and shouldn't, is imply precision you don't have. Don't headline a Scope 3 number built on averages. Don't call a year-on-year change a reduction when it might just be a change in the emission factor someone else updated. Don't claim a product is "low carbon" on the strength of a value-chain estimate. And don't quietly drop the categories where the number looks bad, because selective completeness is just selective disclosure wearing a tie.

The honest version is less impressive on first read. It is considerably more durable on the second.

What to Do Now

A practical sequence, roughly in order, for a business without a dedicated sustainability team.

Start by working out why you're being asked. If it's a specific customer questionnaire, read what they actually need. Often it is your Scope 1 and 2 data, which you may already have or can get quickly, rather than a full Scope 3 inventory. Answer the real question rather than the one you fear.

Measure what you can measure well before you estimate what you can't. Your own energy, travel, and waste are within reach and defensible. Get those solid first. A credible partial picture beats a shaky complete one.

When you do estimate Scope 3, write down your method and keep the working. If you used industry averages, record that. If you later get supplier-specific data, you will want to know what changed and why. This is also what protects you if a claim is ever challenged. The benchmark in green claims enforcement is whether you can evidence what you said, and "we kept the working" is a good answer.

Decide what you'll say publicly, and make it match what you can prove. One honest paragraph about where you are and what you're working on is worth more than a polished report that implies more than you've done.

If your customers are the pressure, get ahead of it. A short, honest supplier statement you can send on request saves you scrambling every time a questionnaire lands, and it tends to read better than a rushed reply.

Common Questions

Do small businesses legally have to report Scope 3?

In most cases, not directly. The disclosure rules target large companies and financial markets. The pressure reaches smaller businesses through the supply chain, when a customer who does have to comply needs your data. The obligation is commercial before it is legal, but it is no less real for that.

Is it greenwashing to report only Scope 1 and 2?

It can be, depending on how you frame it. Reporting Scope 1 and 2 while staying silent on a much larger Scope 3 can read as selective disclosure. The safer approach is to be open about what you've measured and what you haven't, rather than letting the gap speak for you.

Our Scope 3 number is just an estimate. Should we publish it?

You can, as long as you label it clearly as an estimate and say what it's based on. The risk isn't in publishing an estimate. It's in publishing an estimate as if it were a measured fact.

A customer is demanding Scope 3 data we don't have. What do we say?

Tell them what you have, what you're working on, and your timeline. Most customers passing down these requests are managing their own deadline and would rather have an honest partial answer than a fabricated complete one. Silence or a guessed number both tend to cause more problems later.

Will the rules on Scope 3 change?

Yes. The GHG Protocol is revising its Scope 3 standard for the first time since 2011, with a public consultation draft expected in 2026 and a final version targeted for later. The direction is towards more completeness and clearer data quality, not less. That is another reason to keep your working now, so you're not rebuilding from scratch later.

The Thing Worth Holding Onto

Scope 3 is the part of your footprint you have the least control over and the most pressure to talk about. That tension isn't going away. The businesses that handle it well won't be the ones with the most precise numbers, because for most of them precision isn't available yet. They'll be the ones who are clear about what they know, honest about what they don't, and consistent between the two.

My Green Comms helps SMEs communicate sustainability clearly, credibly, and in a way that stands up to scrutiny. If you'd like to see what that looks like in practice, start free at mygreencomms.com.

This article is for informational purposes only and does not constitute legal advice. If you have concerns about your legal accountability for environmental claims, speak to a qualified solicitor.