Scope 3 Emissions: Why They Are So Hard to Measure

Scope 3 Emissions: Why They Are So Hard to Measure

Scope 3 emissions are often the most difficult part of carbon accounting. They include indirect greenhouse gas emissions across a company’s value chain, both upstream and downstream. In simple terms, Scope 3 covers emissions that are connected to the company’s activities but do not come directly from sources the company owns or controls.

The GHG Protocol’s Corporate Value Chain, or Scope 3 Standard, identifies 15 categories of Scope 3 activities, covering areas such as purchased goods and services, transportation, business travel, employee commuting, use of sold products, end-of-life treatment, and investments.

What Makes Scope 3 Different? Scope 3 Emissions Why They Are So Hard to Measure

Scope 1 emissions are direct emissions from company-owned or controlled sources. Scope 2 emissions come from purchased electricity, steam, heat, or cooling. Scope 3 is different because it extends outside the company itself.

For example, a clothing company does not only count emissions from its offices and stores. It may also need to consider cotton farming, fabric production, dyeing, packaging, shipping, customer washing, and disposal of clothes. A bank may need to consider financed emissions linked to lending and investment activities.

This is why Scope 3 is more complex: the emissions often happen in places the company does not directly control.

Problem 1: The Data Comes From Many Different Sources

The first challenge is data collection. Scope 3 information often depends on suppliers, logistics companies, customers, franchisees, investee companies, and other third parties.

A company may know how much electricity it buys for its offices, but it may not know the exact emissions from every supplier’s factory. If suppliers do not measure emissions accurately, the reporting company must use estimates, industry averages, spend-based data, or emission factors.

The GHG Protocol’s Scope 3 Calculation Guidance provides methods, data sources, and worked examples for calculating emissions across the 15 Scope 3 categories, but the quality of the result still depends heavily on the quality of the input data.

Problem 2: The Value Chain Is Large and Complicated

Scope 3 covers both upstream and downstream activities. Upstream emissions happen before the company sells its product or service, such as purchased materials, capital goods, fuel-related activities, business travel, and supplier transportation. Downstream emissions happen after the product is sold, such as product use, waste disposal, franchises, leased assets, and investments.

This creates a boundary problem: companies must decide which activities are relevant, material, and connected to their reporting boundary. A simple product can have a long chain of suppliers, subcontractors, transport routes, and end users.

For many companies, the hardest question is not “What is Scope 3?” but “Where does our responsibility start and stop?”

Problem 3: Estimates Are Often Necessary

Scope 3 measurement often requires estimation. A company may not have exact emissions data for every purchased product, every supplier, or every customer use pattern. As a result, it may use calculation methods based on physical activity data, supplier-specific data, average data, or spend-based estimates.

This does not make Scope 3 useless. It means companies must be transparent about methods, assumptions, data quality, and limitations. Good Scope 3 reporting is not about pretending the numbers are perfect. It is about making the best available estimate and improving the quality over time.

Problem 4: Product Use Can Be Difficult to Predict

Some Scope 3 categories are difficult because they depend on how customers use products. For example, the emissions from a washing machine, car, smartphone, or heating system depend on the user’s behavior, electricity mix, product lifetime, and maintenance.

This is especially important for companies whose products create emissions during use. A product may look low-carbon at the factory stage but have a large climate impact during its lifetime.

Problem 5: Financed Emissions Are Complex

For banks, insurers, and asset managers, Scope 3 Category 15, investments, can be especially difficult. Financial institutions may need to measure emissions linked to loans, investments, or other financial activities. In December 2025, the ISSB issued targeted amendments to IFRS S2 to support implementation of greenhouse gas emissions disclosures, including clarification around Scope 3 Category 15 financed emissions.

This shows that Scope 3 is not only a technical accounting issue. It is also a financial reporting and investor-information issue.

Problem 6: Standards Are Still Evolving

The GHG Protocol is also working on updates to its corporate standards and guidance. Its March 2026 Scope 3 Standard revisions progress update notes that, in September 2025, GHG Protocol and ISO announced a strategic partnership to co-develop greenhouse gas emissions accounting and reporting standards.

This matters because companies need reliable, comparable emissions data, but Scope 3 practice is still improving. Better rules, clearer methods, and stronger data systems should make Scope 3 reporting more useful over time.

How Companies Can Improve Scope 3 Measurement

Companies can improve Scope 3 reporting by starting with the most relevant categories, engaging key suppliers, collecting more primary data, documenting assumptions, improving emission factors, and updating calculations regularly.

They should also avoid treating Scope 3 as a one-time reporting exercise. It should become part of procurement, product design, supplier management, investment analysis, and transition planning.

Conclusion

Scope 3 emissions are hard to measure because they sit across the wider value chain. The data is fragmented, the boundaries are complex, estimates are often needed, and some categories depend on customer behavior or financial exposures.

But Scope 3 is also essential. It often reveals where a company’s biggest climate risks, dependencies, and reduction opportunities are located. In simple terms: Scope 3 is hard because it looks beyond the company’s walls — but that is exactly why it matters.