Scope 3 Supplier Engagement Explained: How Large Organisations Collect Carbon Data from Their Suppliers

If your business has recently been asked to provide a carbon footprint, complete a CDP questionnaire or share emissions data with a customer, you're part of your customer's supplier engagement programme.

Large organisations are under growing pressure from customers, investors, regulators and voluntary initiatives such as the Science Based Targets initiative (SBTi) to understand and reduce emissions across their value chains. For most businesses, the majority of emissions sit outside their own operations, making suppliers central to achieving climate targets.

Companies including Microsoft, Google, BT Group, Royal Mail, Schneider Electric and many others now run structured supplier engagement programmes designed to collect better carbon data, improve the quality of their Scope 3 inventories and support decarbonisation across their value chains.

While every programme is different, most follow a similar pattern. Suppliers are asked to measure their emissions, disclose climate data and, increasingly, demonstrate credible plans to reduce them.

This article explains how these programmes work using Colt Technology Services as a practical example. Colt is a global telecommunications and digital infrastructure company operating across more than 40 countries. Like many multinational organisations, a significant proportion of its emissions occur across its value chain, making supplier engagement a key part of its climate strategy.

Why are organisations asking suppliers for carbon data?

For most large organisations, the majority of greenhouse gas emissions occur outside their own operations.

These Scope 3 emissions come from purchased goods and services, capital goods, logistics, business travel and other activities across the supply chain.

Historically, organisations have estimated these emissions using spend-based emission factors. For example, an organisation might estimate the emissions associated with £1 million of IT equipment by applying an industry-average emissions factor.

This approach provides a useful baseline, but it can't distinguish between suppliers with very different carbon footprints.

Primary emissions data changes that.

Rather than relying on industry averages, it uses emissions calculated from a supplier's own business activities. That allows organisations to:

• improve the accuracy of Scope 3 reporting
• identify suppliers making genuine decarbonisation progress
• understand where emissions occur across the supply chain
• reduce reliance on estimated emissions.

Collecting primary supplier emissions data has therefore become a strategic priority for many organisations.

What does a supplier engagement programme look like?

Although organisations use different platforms and terminology, most supplier engagement programmes follow a similar process.

Colt's 2025 Sustainability Report provides a useful example of each stage.

Case study: Colt's supplier engagement programme

1. Setting expectations through procurement

Supplier engagement starts long before a supplier is asked for emissions data.

Colt embeds sustainability requirements directly into procurement through its Sustainability Schedule.

Suppliers are asked to:

• develop and implement a decarbonisation plan
• set Science Based Targets for Scope 1 and Scope 2 emissions within two years
• align those targets with a 1.5°C pathway.

The company has also revised its supplier engagement target. Rather than expecting suppliers representing 93% of supply chain emissions to set Science Based Targets by 2025, Colt now aims for suppliers representing 70% of supply chain emissions to have set or committed to setting Science Based Targets by 2030. The report says this reflects supplier readiness, changes in its supply chain and updated industry guidance.

This reflects a broader shift in procurement. Sustainability expectations are increasingly becoming part of supplier onboarding, contract management and ongoing supplier relationships.

2. Collecting supplier emissions data

Once expectations have been established, organisations need a consistent way to collect supplier emissions data.

In 2025, Colt joined CDP Supply Chain, using the platform to engage its top 200 suppliers and request carbon footprint information.

The objective is to replace modelled Scope 3 estimates with supplier-specific primary emissions data wherever possible.

CDP is one of several mechanisms organisations use to collect supplier emissions data, alongside supplier portals, procurement systems and sustainability questionnaires.

3. Reviewing data quality

Collecting supplier data is only one part of the process.

Before incorporating supplier emissions into Scope 3 reporting, organisations need confidence that the data has been produced using a credible methodology.

Colt says supplier-specific data was only incorporated where submissions met quality criteria, including:

• carbon footprint verification
• geographical accuracy.

The report doesn't define what "verification" means, but it's clear that Colt applies quality gates rather than accepting every supplier submission automatically. In practice, organisations increasingly expect suppliers to demonstrate that emissions have been calculated using recognised methodologies, supported by a clear audit trail and, in some cases, independent assurance.

As a result, supplier-specific emissions data from 18 suppliers was incorporated into Colt's Scope 3 calculations. Colt says it expects this coverage to increase over time as supplier data availability improves and its engagement programme matures.

Collecting supplier data and collecting usable supplier data are not the same thing.

4. Supporting suppliers

Supplier engagement isn't limited to requesting information.

Colt is also investing in helping suppliers improve their climate capability.

During 2025, the company developed a climate change guidance itinerary that allows suppliers to:

• assess their climate maturity
• understand their current climate practices and commitments
• access tailored guidance.

The programme will be published through Colt's Vendor Portal.

This is one of the most interesting aspects of the report.

Rather than assuming suppliers already know how to measure emissions, Colt recognises that supplier capability varies significantly. Large multinational suppliers often have dedicated sustainability teams. Smaller suppliers frequently do not.

Improving supplier capability is therefore becoming an important part of supplier engagement.

5. Improving Scope 3 data quality over time

Supplier engagement is only one part of Colt's broader Scope 3 strategy.

The report states that Colt aims to:

• increase supplier-specific primary emissions data
• reduce reliance on spend-based estimates
• better reflect suppliers' actual decarbonisation efforts in Scope 3 calculations.

Alongside supplier engagement, Colt is also:

• increasing the use of supplier-specific emission factors
• assessing supplier climate maturity
• improving spend-based calculations by moving from Carbon Trust EEIO emission factors to geographically specific CEDA emission factors where primary supplier data isn't yet available.

Rather than replacing estimated emissions overnight, the strategy is to improve data quality progressively as better supplier information becomes available.

6. Measuring supplier engagement

Supplier engagement is managed as an ongoing business programme rather than a one-off reporting exercise.

Colt tracks a range of performance indicators, including:

• 64% of supply chain emissions linked to suppliers that have set Science Based Targets, committed to setting them or signed Colt's Sustainability Schedule
• 73% of suppliers engaged on ESG topics
• 85% of suppliers accepting Colt's Supplier Code of Conduct
• 94% of procurement spend covered by contracts containing environmental, labour and human rights requirements.

These metrics demonstrate that supplier engagement is increasingly being managed in the same way as any other strategic procurement programme.

What this means for suppliers

If a customer asks for your carbon footprint, they're rarely asking out of curiosity.

They're trying to improve the quality of their own climate reporting, reduce uncertainty in their Scope 3 emissions and understand which suppliers are making progress on decarbonisation.

That means supplier engagement programmes are likely to become more common, more structured and more consistent over the next few years.

For suppliers, the expectation isn't necessarily that you already have perfect carbon data.

The expectation is increasingly that you have a credible approach to measuring emissions, can explain your methodology and can improve the quality of your reporting over time.

The missing piece: supplier capability

Reading sustainability reports from organisations like Colt reveals a consistent pattern.

Large organisations have invested in:

• procurement requirements
• supplier engagement platforms
• CDP Supply Chain
• supplier guidance
• climate maturity assessments
• data quality controls
• supplier performance metrics.

The enterprise side of supplier engagement is becoming increasingly sophisticated.

The remaining challenge is supplier capability.

Many SMEs and mid-market businesses don't have dedicated sustainability teams or in-house carbon accounting expertise. Measuring emissions often requires information from finance, procurement, operations, facilities and travel, alongside an understanding of recognised carbon accounting standards.

Helping suppliers develop that capability is likely to become just as important as the technology used to collect their data.

Responding to a customer's carbon request?

Whether you've been asked to complete a CDP disclosure, answer a supplier questionnaire or share your carbon footprint, the first step is to produce a robust, activity-based footprint using a recognised methodology.

Seedling helps SMEs and mid-market organisations measure GHG Protocol-aligned carbon footprints through software and expert support designed for businesses without dedicated sustainability teams.

The result is carbon data that's credible, transparent and ready to share with customers.

→ Talk to us about how we can help

Responsible for supplier engagement?

Most enterprise carbon accounting platforms help you collect supplier emissions data.

Seedling helps suppliers produce it.

We help SME suppliers measure GHG Protocol-aligned primary emissions data through software and expert support, giving sustainability teams access to higher-quality supplier data without increasing the burden on internal teams.

If you're looking to improve primary supplier data quality or increase participation across your supplier engagement programme, we'd be happy to share what we're seeing across the SME supplier landscape.

→ See how we help with supplier engagement

FAQs

What is a supplier engagement programme?‍

It's the structured process large organisations use to collect emissions data from their suppliers, review its quality, and support suppliers in improving it over time. Companies including Microsoft, BT Group, Royal Mail and Colt run these programmes to build a more accurate picture of their Scope 3 emissions and support decarbonisation across their value chains.

Why is a customer asking us for our carbon footprint?

For most large organisations, the majority of emissions sit in Scope 3, outside their own operations. Asking suppliers for emissions data helps them replace industry-average estimates with supplier-specific figures, improve the accuracy of their reporting, and identify which suppliers are making genuine progress on reducing emissions. If you've been asked, you're part of that

What is the CDP Supply Chain?

CDP Supply Chain is a disclosure platform organisations use to request carbon footprint information from their suppliers at scale. In 2025, Colt joined CDP Supply Chain to engage its top 200 suppliers. It's one of several mechanisms organisations use, alongside supplier portals, procurement systems and standalone questionnaires.  customer's supplier engagement programme.

How good does our carbon data need to be?

Customers increasingly apply quality gates rather than accepting every submission. Colt only incorporated supplier-specific data where it met criteria such as footprint verification and geographical accuracy. In practice, that means emissions calculated using a recognised methodology like the GHG Protocol, supported by a clear audit trail and, in some cases, independent assurance.

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