Your base year is the year you measure progress against. Everything you claim about reduction is relative to it.
Choosing a base year
Pick the earliest year for which you have data you trust.
Two tests:
Is it complete? A base year missing a category makes every future comparison wrong in the same direction.
Is it representative? A year with a plant shutdown or an unusual event makes your progress look better than it is.
If your earliest year fails either test, use a later one and say why.
In Avarni, set it under Forecasting, as the Baseline Year. You set the start date and the year runs from there.
Base year and comparative are not the same
Your comparative is the immediately prior period, shown beside this year's figures. It moves every year.
Your base year is fixed, and is what your targets are measured against.
One year is often both, in your second year of reporting. After that they separate.
When to recalculate your base year
Recalculate when something changes that makes the comparison misleading rather than meaningful.
The usual triggers:
A structural change to your group, such as a significant acquisition or disposal
A change in your calculation method
A change in your boundary, such as adding a category you previously excluded
Discovering a material error in the base year
Do not recalculate because emission factors were updated, or because your business grew or shrank. Those are real changes and should show.
Set a threshold and write it down
Decide how large a change has to be before you recalculate. Many organisations use a percentage of total base year emissions, commonly 5%.
Write the threshold into your Basis of Preparation and apply it consistently. A threshold applied only when the result is favourable will be challenged.
How to restate
Recalculate the base year as if the change had always applied.
Restate every year between the base year and now, on the same basis.
Record what changed, why, and the effect on each year.
Present both figures in your disclosure for the year of the change, so a reader can see the step.
Excluding something from the base year
If you sold a division, you remove it from the base year as well as the current year. Otherwise your reduction includes the disposal, which is not a reduction.
The same applies to a data centre, a site or a product line you no longer have.
Comparability after a method change
If you move a category from spend-based to activity data, your figure will move, and the movement is a method change rather than a real one.
Either restate the prior year on the new method, or state clearly that the change is not comparable. Restating is better.