Most organisations have made decent progress on Scope 1 and 2 emissions. Switch to renewable electricity, upgrade the heating system, electrify the vehicle fleet—the path is clear even if execution takes time. These are emissions you control directly, and the solutions are increasingly well-understood.

Then there's Scope 3. The emissions embedded in everything you buy. The carbon footprint of your supply chain. For most organisations, this represents 70-90% of their total emissions. And it's vastly more complicated than anything you've tackled before.

What Scope 3 Actually Includes

The Greenhouse Gas Protocol defines 15 categories of Scope 3 emissions. Purchased goods and services. Capital goods. Fuel and energy activities. Transportation and distribution. Waste generated in operations. Business travel. Employee commuting. Leased assets. Processing of sold products. Use of sold products. End-of-life treatment. Franchises. Investments.

Some categories are straightforward to conceptualise even if hard to measure—the carbon embedded in the materials you buy, for instance. Others are more complex—the emissions from customers using your products over their lifetime, or the full footprint of financial investments.

For most organisations, purchased goods and services dominates. What you buy determines your Scope 3 footprint more than any other factor. Which means your supply chain is the key to any serious carbon reduction strategy.

The Measurement Challenge

You can't manage what you can't measure. But measuring Scope 3 emissions is genuinely difficult.

For your own operations, you have data. Electricity bills tell you consumption. Fuel purchases tell you vehicle emissions. You control the systems that generate this information.

For your supply chain, you're dependent on suppliers for data—suppliers who may not have it, may not want to share it, or may not calculate it the same way you would.

The typical starting point is spend-based estimation. Take your procurement spend by category, multiply by emission factors derived from economic input-output analysis, and get a rough footprint. This works as a baseline but is highly approximate. Two suppliers in the same category might have vastly different actual emissions.

Supplier-specific data is more accurate but harder to obtain. Asking suppliers for their carbon data requires them to have it, which many don't. Even those with sophisticated sustainability programmes may struggle to allocate emissions to specific customers or products.

Hybrid approaches combine methods—spend-based estimation as a foundation, supplier-specific data where available, product-level life cycle assessments for key items. The result is imperfect but progressively improving.

The PPN 06/21 Driver

UK organisations bidding for major government contracts now face Procurement Policy Note 06/21, which requires carbon reduction plans from suppliers. Contracts above £5 million must include evaluation of the supplier's carbon approach.

This isn't just aspiration—it's commercial requirement. Suppliers without credible carbon reduction plans will lose government contracts to those who have them. The policy is cascading through supply chains as prime contractors push requirements to their subcontractors.

PPN 06/21 doesn't mandate specific Scope 3 approaches, but credible carbon reduction plans must address supply chain emissions. You can't claim to be reducing carbon while ignoring 80% of your footprint.

For many suppliers to government, this regulatory push has been the catalyst for serious Scope 3 work. Not environmental idealism—commercial necessity. The requirements are real, and the consequences of non-compliance are lost business.

Starting the Journey

Where do you begin with something this large and complex? The honest answer is: wherever you can, with whatever data exists, improving over time.

Baselining spend-based emissions gives you a starting point and identifies priority categories. Which categories represent the largest portions of your estimated footprint? Those deserve focus first.

Engaging key suppliers on carbon data creates the foundation for improvement. You probably have 50-100 suppliers who represent the vast majority of your spend. Start there, not with the entire supplier base.

The conversation with suppliers matters as much as the data request. Many suppliers are on their own sustainability journeys. They may appreciate guidance on what data to collect and how to calculate emissions. Collaboration beats demands.

Setting expectations for new suppliers builds carbon into normal procurement. Requiring carbon data as part of onboarding ensures new relationships start with visibility. Existing suppliers may take longer to bring into compliance.

The Reduction Strategies

Measurement enables reduction, but measurement alone changes nothing. What actually reduces Scope 3 emissions?

Switching to lower-carbon suppliers is the most direct approach. If Supplier A has half the carbon intensity of Supplier B for equivalent products, switching cuts your emissions. This only works if you have supplier options and can compare their footprints accurately.

Helping existing suppliers reduce emissions often has greater impact. Many of your suppliers face the same challenges you do. Sharing knowledge, setting expectations, and sometimes providing support can enable improvements across your supply chain.

Product and specification changes can dramatically affect embedded carbon. Using recycled materials, designing for longevity, specifying efficient products—these choices flow through supply chains as reduced emissions.

Reducing consumption addresses root cause. The lowest-carbon product is the one you don't buy. Challenging whether purchases are necessary, extending product life, and eliminating waste reduce emissions more effectively than switching to greener alternatives.

The Data Infrastructure

Serious Scope 3 management requires data infrastructure that most organisations don't yet have. Supplier carbon data needs to be collected, validated, stored, and analysed. This integrates with procurement systems, sustainability reporting, and supplier management processes.

The technology landscape is evolving rapidly. Platforms for supplier carbon data collection, databases of emission factors, tools for life cycle assessment—options are multiplying. But technology alone doesn't solve the problem. Processes, policies, and people matter more.

Building capability takes time. Most organisations are early in this journey. The important thing is to start, learn, and improve rather than waiting for perfect solutions that will never arrive.

The Honest Reality

Scope 3 is hard. The measurement challenges are real. The data gaps are genuine. The complexity is not exaggerated. Anyone who tells you there's a simple solution is either selling something or doesn't understand the problem.

But hard is not impossible. Organisations that start now, accept imperfect data, and improve progressively will be far ahead of those who wait for perfect solutions. Regulatory pressure is increasing. Customer expectations are rising. Competitive advantage accrues to those with credible carbon strategies.

The organisations that will thrive are those treating Scope 3 as a strategic priority rather than a compliance burden. They're building supplier relationships around carbon. They're making purchasing decisions with emissions in view. They're investing in capability now rather than scrambling later.

Scope 3 is the big challenge. It's also the big opportunity—for environmental impact, for competitive differentiation, and for building the supply chain capabilities that will define success in a carbon-constrained future.