MnrAq

Annex 5
Details for Section 1.5.2:
bottom-up inventory uncertainty
analysis
Sources of uncertainty in the Second IMO GHG Study 2009
In the Second IMO GHG Study 2009, the method relied upon weighted average values for each ship/size
category. As such, much of the uncertainty in that study was related to aleatory uncertainty. This limited the
ability of that work to quantitatively characterize uncertainty, although some key aleatory uncertainties could
be characterized with distributions around computed average values.
The Second IMO GHG Study 2009 relied upon a set of independent estimates to define a confidence range
on the central estimate for fleetwide fuel use and emissions. It also discussed uncertainties in calculating
total emissions (Second IMO GHG Study 2009, Table 3.1). It reported that a dominant source of uncertainty
included assumptions about average main operating days, and that a secondary source of uncertainty was
average main engine load. Both of these were applied in common to all ships in a type and size category.
The study reported that better AIS collection and better quality control on AIS-reported speed were needed
to reduce uncertainty. Lastly, the Second IMO GHG Study 2009 reported a number of uncertainties with
auxiliary engine calculations.
Overview of sources of uncertainty in current work
Figure 26 illustrates where potential uncertainty is introduced into the bottom-up model for this update. Table
17 (adapted from Jalkanen et al., 2013) identifies examples of uncertainties and relates these to explicit QA/
QC efforts that reduce uncertainty.