Calculating Supply Chain Emissions: Key Factors & Data Sources

Calculating Supply Chain Emissions
Calculating Supply Chain Emissions

Supply chain emissions, also known as scope 3 emissions, refer to the greenhouse gas emissions that occur across a company’s upstream and downstream value chain. These emissions often represent the majority of a company’s carbon footprint. Accurately calculating scope 3 emissions is crucial for setting science-based targets, choosing suppliers, and reducing impacts.

Key Steps for Calculating Supply Chain Emissions

The main steps for calculating supply chain emissions are:

  1. Map the supply chain – Identify major suppliers, materials, logistics, and services. Focus on the largest contributors first.
  2. Collect activity data – Gather procurement spend, weight purchased, units procured, or other metrics on volumes.
  3. Identify emissions factors – Find appropriate emissions factors for materials and services. Key sources are:
    • EPA supply chain factors for US industries1
    • Ecoinvent life cycle database
    • Industry associations
    • Supplier surveys
  4. Calculate emissions – Multiply activity data by emissions factors to estimate emissions for each supplier and category.
  5. Improve accuracy – Collect primary data from suppliers through surveys or product LCAs. Prioritize the largest contributors.
  6. Set reduction targets – Analyze results to find hot spots and set science-based targets to reduce emissions over time.
  7. Track progress – Update activity data annually and compare to baseline to track target progress.

Emissions Factors Data Sources

Some key emissions factors data sources are:

  • EPA Supply Chain Factors – Provides cradle-to-gate factors for over 400 US industries based on EEIO modeling. Covers emissions from inputs, transport, and waste.
  • Ecoinvent Database – Contains thousands of product and industry life cycle assessment profiles with emissions factors. Requires a license.
  • Industry Associations – Groups like WBCSD provide industry average emissions factors for specific materials and products like cement, steel, aluminum.
  • Supplier Surveys – Asking suppliers directly for emissions factors through questionnaires or scorecards.

Challenges and Limitations

Some key challenges with emissions factors include:

  • Reliance on proxy data and industry averages due to limited supplier data
  • Emissions estimates are not product or supplier specific
  • Evolving accounting standards and platforms
  • High effort required to survey small suppliers
  • Legal and competitiveness concerns around data sharing

Ongoing collaboration across the value chain is needed to enable more accurate and transparent emissions accounting.

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