Third IMO Greenhouse Gas Study 2014

60 Third IMO GHG Study 2014
1.4 Quality assurance and control of top-down and bottom-up inventories
The quality analysis is presented in three sections. The first section discusses QA/QC for the top-down
emissions inventory. The second section summarizes the QA/QC elements of the bottom-up fuel and emissions
inventory. The third section contains a comparison of the top-down and bottom-up emissions inventories.
Sections 1.1 and 1.2 contain many detailed processes that constitute QA/QC effort; these sections therefore
discuss QA/QC mainly in summary and provide context for the quantitative bottom-up uncertainty analysis
in Section 1.5.
1.4.1 Top-down QA/QC
Top-down statistics were evaluated for transparency and any significant discrepancies that might reflect
confidence in inventories based on fuel statistics.
This section begins with a review of the Second IMO GHG Study 2009 and a brief discussion of data quality,
confidence and uncertainty. It reviews relevant data quality information provided by IEA, including information
about likely causes of potential under- or overestimation of marine fuel use (both domestic and international).
Top-down method QA/QC efforts undertaken specifically for this study are described. Lastly, this section
gives a QA/QC summary of the study.
Second IMO GHG Study 2009: review of top-down data quality
The Second IMO GHG Study 2009 performed qualitative analyses of errors and inconsistencies of IEA statistics
to help explore how the top-down and bottom-up discrepancy may be explained by uncertainty in reported
fuel statistics. That study identified the following potential issues with top-down data:
• different data quality between OECD and non-OECD countries (fishing);
• identical numbers from year to year for some countries;
• big swings from year to year for other countries;
• differences in EIA bunkers statistics.
Although a number of challenges were recognized, mainly arising from the use of different data sources, the
sources of uncertainty remained unexplored and potential corrections were not attempted.
The Second IMO GHG Study 2009 explicitly quoted provisions in the IEA Agreement on an International
Energy Program (IEP) that determined which fuels would be considered in national oil stocks and which were
considered to be counted as international data. In particular, international marine bunkers were “treated as
exports under a 1976 Governing Board decision incorporated into the Emergency Management Manual”
(Scott, 1994). This information and subsequent discussion in the Second IMO GHG Study 2009 suggested that
some degree of allocation error among international bunkers, exports and/or imports could be a factor in the
accuracy of top-down fuel statistics for shipping.
IEA statistics: review of top-down data quality
IEA collects data from OECD countries that have agreed to report mandatory data through monthly and joint
annual IEA/Eurostat/UNECE questionnaires. For non-OECD countries, IEA collects data through voluntary
submissions (using no standard format) or through estimates made by IEA or its contractors. Figure 43 presents
a map of OECD and non-OECD countries that provide energy data to IEA; not all of these countries have
marine fuel sales to report (Morel, 2013).