The GHG Protocol is widely used because it gives companies a shared accounting structure for Scope 1, Scope 2, and Scope 3 emissions. But the framework only becomes audit-ready when every calculation can be traced from output back to source data, factor, method, and approval.
The basic calculation is simple: activity data multiplied by an emission factor. The hard part is governing every choice around that calculation. Was the activity data measured, estimated, or allocated? Which factor source was used? Which year and geography does the factor represent? Were unit conversions applied correctly? Was the Scope 2 calculation market-based, location-based, or both? Were Scope 3 assumptions documented?
Audit-ready calculations require:
- Source activity records.
- Factor source and version.
- Unit conversions.
- Method selection.
- Scope and category.
- Organizational and operational boundary.
- Reviewer and approver.
- Change history.
- Exception handling.
Manual programs tend to collapse these details into a final number. That may work for a management dashboard, but it breaks under assurance. Assurance teams need to test lineage, not just totals.
Hydrus connects calculation outputs to inputs. Teams can ingest data from email, APIs, OCR, uploads, ERP, utilities, travel, procurement, and supplier files. Emission factors are selected and preserved with the calculation. Scope 1, Scope 2, and Scope 3 records retain data lineage and review history.
This is especially important for Scope 2 and Scope 3. Market-based Scope 2 requires contractual and supplier-specific evidence where used. Scope 3 often requires estimation methods and data-quality scoring. The methodology needs to be visible, not buried in a spreadsheet formula.
The best carbon accounting systems make every number explainable: what it is, where it came from, how it was calculated, who reviewed it, and what changed since the last report.
This guide is educational and not assurance advice.