Companies need to select and report a base year with verifiable emissions data. This serves as a reference point to compare future emissions and track progress.

Companies may choose a single year or an average of several years as their base year to account for fluctuations in GHG emissions.

Companies should develop a base year emissions recalculation policy detailing when and how recalculations will be done.

Significant structural changes (like mergers or acquisitions) or errors discovered in historical data often require recalculating the base year emissions.

A "significance threshold" is used to decide whether changes are substantial enough to warrant recalculation.

Recalculations should align with business goals and context.

Companies subject to external GHG programs may have specific rules governing base year choice and recalculations.

For internal management goals, companies can follow the GHG Protocol guidance or develop their own consistent approach.

Structural changes: Such as acquisitions or divestments that significantly alter the company's base year emissions.

Methodology Changes: If new, more accurate methods or emission factors significantly affect base year data.

Discovery of Errors: Significant errors or numerous smaller errors that collectively impact base year emissions.

No recalculations are needed for facilities not existing in the base year or for organic growth or decline as they reflect real changes in emissions.

Companies may optionally report recalculated GHG emissions data for all years between the base year and the reporting year, alongside the original figures.