GHG base year and recalculation: when to restate past emissions

A base year is the reference against which you measure progress. Targets such as "reduce Scope 1 and 2 by 42% from 2024" only mean something if the 2024 figure is solid and stays comparable. See science-based targets explained for how targets use it.

Choosing a base year

The Corporate Standard says: "Companies shall choose and report a base year for which verifiable emissions data are available". Pick the earliest year for which you have complete, reliable data for all the emissions in your target boundary, rather than a year that merely looks convenient. Some companies use an average of several years to smooth out unusual events.

When you must recalculate

The standard requires base year emissions to be recalculated when any of these has a significant effect:

1. "Structural changes in the reporting organization that have a significant impact on the company's base year emissions", including "Mergers, acquisitions, and divestments" and "Outsourcing and insourcing of emitting activities".
2. "Changes in calculation methodology or improvements in the accuracy of emission factors or activity data".
3. "Discovery of significant errors, or a number of cumulative errors, that are collectively significant."

What does not trigger recalculation

"Base year emissions and any historic data are not recalculated for organic growth or decline." If you open a new factory or close a production line, your emissions go up or down for real, and the base year stays as it was.

The significance threshold

Your recalculation policy "shall state any "significance threshold" applied for deciding on historic emissions recalculation". A common form is a percentage of base-year emissions. Whatever you choose, write it down before you need it, so the decision is not made after seeing the results.

Worked example

Base year 2024: Scope 1 and 2 = 10,000 t CO2e. In 2026 the company acquires a business that emitted 1,500 t in 2024.

• Without recalculation, 2026 emissions of 10,800 t would look like an 8% increase.
• With recalculation, the base year becomes 11,500 t (adding the acquired business's 2024 emissions), and 10,800 t is a 6% reduction.

The recalculated figure is the honest comparison.

Emission factor updates

Grid factors change every year, which is real change in the grid, not an error, so use each year's factor for that year. But if a factor provider corrects a past factor, or you switch to a better method (for example from spend-based to supplier data for a large category), that is a methodology change: assess whether it is significant and, if so, recalculate the base year on the new basis.

In LCALens

Inventories keep each calculation with its factor, source, code version and input hash, and a locked inventory keeps its frozen snapshot. That makes it possible to show exactly what changed between the original and the recalculated base year.