Emission sources — and the underlying emission factors that power them — are the crux of carbon accounting. They are the foundation for measuring and managing emissions, and understanding how to choose and apply them is essential for carbon accounting.
👉 If you’re new to this space, we recommend starting with:
- [Carbon Accounting 101] for a plain-language overview.
- The Introduction to Carbon Accounting course in the Sumday Academy for an in-depth breakdown of Carbon Accounting.
With that foundation, this article will guide you through how emission sources and emission factors work in practice, how Sumday approaches them, and how to decide which ones to use when coding transactions.
1. Refreshing the basics: What Are Emission Factors?
Emission factors are the magic numbers that let you estimate your carbon emissions from the business data you already have — like spend, fuel use, or electricity consumption. They represent the average greenhouse gas (GHG) emissions associated with a specific activity, product, or service.
Examples:
- $20,000 on packaging × emissions factor = 50 tonnes CO₂-e
- 1,000 kWh of electricity × emissions factor = 170 kg CO₂-e
You might also hear them called conversion factors, emissions intensity, or carbon intensity. They’re the foundational building blocks of carbon accounting.
2. Why There’s No Single “Right” Answer
Emission factors from industry databases are usually based on high-level industry averages — not your supplier’s actual emissions. This means:
- There isn’t always a perfect match.
- What matters is choosing the closest reasonable fit and staying consistent over time.
- The long-term goal is to replace these industry average conversion factors with supplier-specific data as it becomes available - see here for more.
3. How Sumday Helps You Choose
Default Datasets
When you create an assessment, Sumday automatically applies default datasets based on your region. These are public, reputable sources such as:
- AUS DCCEEW (Australia)
- UK DESNZ (United Kingdom)
- US EPA (United States)
- NZ Ministry for the Environment (New Zealand)
- EXIOBASE (global coverage)
Coding Transactions in the Carbon Ledger
- Emission sources are sometimes broad (e.g. Forestry Products) and sometimes specific (e.g. Concrete). Transactions, too, can range from broad categories (like Consulting) to very specific line items (like Paper purchases).
- The aim is to match the best reasonable fit between your transaction and an emission source.
- In the Carbon Ledger, Sumday's Smart Suggestions will read details of the Description, Supplier and General Ledger account and suggest which emission source may be most relevant and provide a confidence score.
- If there isn’t an exact match, choose the closest reasonable fit and be consistent going forward.
Checking Factor Details
- In the Carbon Ledger, when you select an emission source, the right-hand pop-out shows:
- The underlying emission factor
- The calculation unit
- The source link for full transparency
- This helps guide your choice and highlight future opportunities to improve.
- For Emission Sources in the Accounting tab, further details can be found in the Emission Database table.
Searching Across Datasets
If you want to see what other emission sources might be available from other datasets in Sumday
- Click the grid icon (top right) → open the Master Emission Factor Table.
- Filter by Scope (e.g. Scope 3) and search keywords (e.g. aggregate, paper).
- If you find a better-suited factor, add the dataset via Assessment Settings.
Adding Custom Factors
- If no suitable factor exists in the default datasets, you can import them manually.
- For example, supplier specific emission factors, or an emission factor from an industry-specific database or a licensed data source.
4. Engaging with Suppliers
Industry averages are a starting point, but the goal is supplier-specific emission factors (primary data). Example:
- For every litre of milk purchased from Milky Way Ltd, emissions = 2 kg CO₂e.
This approach is recognised by the GHG Protocol as the most accurate method. Sumday’s Supplier Engagement Tool helps you reach out with one simple question: “Are you carbon accounting?”
5. Practical Tips for Decision-Making
- If there’s no perfect match → pick the closest reasonable factor and move forward.
- Stay consistent year-on-year unless you have strong reason to change.
6. The Journey: Improving Data Quality Over Time
Carbon accounting is about progress, not perfection:
- Start with industry averages — they’re good enough to begin measuring.
- Improve over time by collecting supplier-specific data.
- Each year, your data gets more accurate as you engage suppliers and refine your processes.
By starting today — even with imperfect data — you’ll be on the path toward more meaningful, supplier-specific carbon accounting. The key is to begin, stay consistent, and improve step by step.