The results of your GHG inventory are not completely accurate. There are several sources of uncertainty.
Emission Factors
Calculating an emission factor is inherently uncertain and is based on numerous assumptions and calculation choices. Each emission factor may therefore be more or less reliable.
Emission factor databases are not exhaustive: in some cases, the temporal, geographical or technological granularity is not precise enough.
Emission Factor Selection
The choice of emission factors can also be a source of uncertainty and error.
For a given quantity or amount, several similar and relevant emission factors with different values may exist.
An incorrect emission factor may be selected.
Activity Data
No uncertainties linked to expenses, these amounts are exact.
However, activity data that is provided by a reporting company can be inaccurate and uncertain. For example, the distance travelled by truck or the quantity of steel purchased are often estimated values.
Methodology
The expense-based approach has a higher level of uncertainty than the activity one. We therefore encourage reporting companies to always favour activity-based studies whenever possible.