In the first article of this series, we discussed building a sound Scope 1 and Scope 2 inventory as the foundation of greenhouse gas reporting. The next question small and medium enterprises face is more complex: when should we begin addressing Scope 3?

Scope 3 emissions occur across a company’s value chain, both upstream and downstream. Under the Greenhouse Gas Protocol, there are fifteen categories, ranging from purchased goods and capital equipment to transportation, product use, and end-of-life treatment of products. For most organizations, Scope 3 represents the majority of total greenhouse gas emissions. Yet it is also the least controlled scope and often the most difficult to quantify.

For SMEs, Scope 3 typically enters the conversation because of external pressure. A major customer requests value-chain data. A corporate client begins setting science-based targets and pushes requirements downstream. A disclosure platform references Scope 3 expectations. The result is often uncertainty about what to quantify.

In practice, not every SME needs to conduct a comprehensive Scope 3 inventory at the outset; the appropriate pace depends on a few triggers.

You should begin actively assessing Scope 3 when:

• A key buyer requests Scope 3 data or signals upcoming requirements.
• Your organization intends to set science-based targets.
• You operate in a sector where value-chain emissions are structurally significant (for example, manufacturing, food, logistics, or consumer goods).
• You are preparing for external disclosure that requires transparency around relevant categories.

If these conditions are not present, abrupt full-scale quantification may create unnecessary complexity. However, ignoring Scope 3 is not a defensible long-term position. Even if reporting is not yet required, understanding likely value-chain exposure is strategically safe.

The critical issue is sequencing.

A stable Scope 1 and Scope 2 foundation provides internal governance, boundary clarity, and methodological discipline. Without this structure, Scope 3 calculations risk becoming fragmented and inconsistent. With it, organizations are in a better position to assess value-chain emissions in a structured way.

In the next article, we will examine how SMEs can approach Scope 3 pragmatically: beginning with a screening assessment, benchmarking against peers, and prioritizing the most relevant categories before moving toward detailed quantification.

If your organization is beginning to receive value-chain data requests, an early and structured assessment can prevent rushed, misaligned, and ultimately costly reporting decisions.