Parties should provide documentation on source and/or sink categories that have been excluded from their inventory submission. Although national inventories are intended to be a comprehensive assessment of anthropogenic sources and sinks of greenhouse gas emissions and removals, some sources and sinks are excluded from the estimates presented for various reasons.

These reasons, in many cases, will be legitimate. For example, it may be the case that there is no primary aluminum smelting activity taking place within a particular country.
However, it is important to note that processes or activities that are not anthropogenic in origin or do not result in a net source or sink of greenhouse gas emissions are intentionally excluded from a national inventories according to the Revised 1996 IPCC Guidelines. In general, processes or activities that are not anthropogenic are considered natural (i.e., not directly influenced by human activity) and, as an example, would include the following:

·         -Volcanic eruptions
·         -Carbon dioxide (CO₂) exchange (i.e., uptake or release) by oceans
·         -Natural forest fires[1]?
·         -Methane (CH₄) emissions from wetlands not affected by human induced land-use changes

Some processes or activities may be anthropogenic in origin but do not result in net emissions of greenhouse gases, such as the respiration of CO₂ by humans or domesticated animals.[2] Given a source or sink category that is both anthropogenic and results in net greenhouse gas emissions or removals reasons for excluding an activity include one or more of the following:

·         -There is insufficient scientific understanding to develop a reliable method for estimating emissions at a national level.
·         -Although an estimating method has been developed, data were not adequately available to calculate emissions.
·         -Emissions were implicitly accounted for within another category (e.g., CO₂ from Fossil Fuel Combustion).

In keeping with the principles above, you should check if any source or sink categories (or sub-categories) are missing from a Party’s inventory. You should also be critical of Party’s explanation (or lack of explanation) for this exclusion until you are confident that it is appropriate.

An important distinction to keep in mind when reviewing a Party’s CRF tables is the difference between the notation keys “NO” and “NE”.  When a Party uses “NO” it is reporting that the activity associated with the specific source or sink category does not occur anywhere within the Party’s territories.  Because the activity does not occur, emissions or removals are necessarily zero.  Parties should only report “NO” when they are highly confident that the relevant activity does not occur within the country.