A base year is the historical reporting period against which a company tracks its emissions performance over time. It is the reference point for any reduction target — for example, "50% reduction by 2030 against a 2020 base year."
A base year restatement is the recalculation of the base-year footprint to maintain like-for-like comparability when something material changes — typically a structural change (acquisition, divestiture, restructuring), a discovery of a significant data error, or a change in calculation methodology.
Why it matters
Without restatement, a company that acquires a new subsidiary could appear to increase its emissions even if every existing operation has reduced them. The acquisition adds new emissions to the current year that were never in the base year — a misleading comparison. Restating the base year to include the acquired entity restores the like-for-like view.
The GHG Protocol requires companies to define a clear restatement policy at the outset (the threshold for what triggers a restatement) and to apply it consistently. PPN 006 and most disclosure frameworks expect restatements to be documented and explained.
A practical example
A company sets 2020 as its base year with a footprint of 1,000 tCO₂e. In 2023 it acquires a subsidiary that adds another 300 tCO₂e to its current operations. Without restatement, the 2023 footprint of 1,300 tCO₂e looks like a 30% increase. After restating the base year to include the subsidiary's 2020 emissions (say 280 tCO₂e), the like-for-like 2020 baseline becomes 1,280 tCO₂e — and the 2023 figure now shows a small reduction, not a large rise.
We define base year and restatement policy on every engagement. See how it fits into ongoing support on the methodology page.