Third IMO Greenhouse Gas Study 2014
GHG3%20Executive%20Summary%20and%20Report
GHG3%20Executive%20Summary%20and%20Report
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Annex 4 231<br />
IEA sources of uncertainties that can be quantified for this work<br />
As mentioned in Section 1.5.1 of the main report, IEA energy balance statistics represent the best available<br />
top-down numbers that include marine bunker fuels estimates on a global basis. We assess the quality of IEA<br />
by looking at possible sources of uncertainties, and by estimating the potential correction when it is feasible.<br />
We identify four important sources of top-down marine fuel uncertainties:<br />
1 Maritime sector reporting: fuel sales distinguish between international and domestic navigation<br />
categories with uncertainty. Errors can be made when fuels reported under different categories are<br />
combined. This type of error can be spilt in two cases:<br />
a<br />
b<br />
Misallocations: Fuels that should be attributed to national navigation are allocated in international<br />
navigation or vice versa. In this case, only the total (sum) of sales per type of fuel is correct, while<br />
the allocation is uncertain.<br />
Duplications: Fuel sales could be allocated in both categories, double-counting the amount of<br />
fuel sold. In this case, the allocation and fuel totals can contain errors contributing to uncertainty.<br />
2 Other sector misallocation: marine fuels might be allocated to other non-shipping categories, e.g.<br />
export, agriculture, etc. In this case, marine fuels would be under-reported and other sectors may<br />
have their fuels over-reported.<br />
3 Transfers category reporting: in accordance with IEA, this category comprises inter-product transfers,<br />
which result from reclassification of products either because their specification has changed or<br />
because they are blended into another product. The net balance of inter-product transfers should be<br />
zero; however, “National stocks” can be used in blending residual bunkers to specification. This could<br />
increase the volume of fuel delivered to ships sometimes without statistical documentation (IEA,<br />
2013), resulting in under-reporting.<br />
4 Data accuracy: IEA data may suffer a lack of intrinsic accuracy because of the ways in which the data<br />
are collected.<br />
These sources of discrepancy are not mutually exclusive, and not all of them can be identified and quantified<br />
given available data at the national levels.<br />
Estimates of potential adjustment to top-down statistics<br />
Potential adjustments are evaluated by considering world energy statistical balances, and quantifying<br />
discrepancies in quantities most related to known top-down uncertainty. We quantify sector misallocation<br />
specifically for cumulative volumes that could be misallocated marine bunkers, in whole or in part.<br />
Export-import misallocation<br />
Some of energy allocation discrepancies can be identified through analysing IEA data in world balance format.<br />
We use these discrepancies to estimate potential corrections due to uncertainties that are under the category<br />
“other sector misallocation”.<br />
As acknowledged by IEA, the difference between total exports and imports (net difference at world scale)<br />
indicates a possible misallocation of bunkers into exports for some countries. By collecting IEA data in<br />
world balance format, this net difference at world scale can be used to identify an upper bound of potential<br />
correction. Given evidence that at least part of this discrepancy could be from a misallocation of marine fuels,<br />
we expect that the best estimation of this uncertainty would adjust the fuel sale data. In other words, if excess<br />
exports are not recorded as imports, then excess fuel deducted as exports could be sold as marine bunkers<br />
without record.<br />
The net discrepancies reported by IEA as “Statistical differences” are calculated as total consumption minus<br />
total supply. Figure 20, Figure 21 and Figure 22 show the marine fuel sales data and both discrepancies over the<br />
period 1971–2011. The net statistical difference should be expected to be smaller than any single contributor<br />
to the net differences. This is because net statistic difference includes the export-import discrepancy, and all<br />
other discrepancies that may be additive or offsetting, including unquantified discrepancies (uncertainties) in<br />
marine bunker statistics.