Third IMO Greenhouse Gas Study 2014

Inventories of CO2 emissions from international shipping 2007–2012 93
Figure 70 demonstrates good agreement between the various components of the calculation of fuel
consumption. This provides evidence that observed good agreement in total fuel consumption is underpinned
by good agreement in model design. These crossplots are most directly related to the international shipping
totals reported in Figure 66. This is because the crossplots are limited to vessel categories that are known to
be engaged in international shipping and where the Third IMO GHG Study 2014 categories can be directly
matched to categories reported in 2009 study.
a) Main engine fuel consumption b) Total vessel fuel consumption
c) Vessel type annual fuel c) Vessel type annual CO 2
Figure 70: Crossplots for main engine annual fuel consumption, total vessel annual fuel consumption,
aggregated vessel type annual fuel consumption and CO 2 for the year 2007,
as reported by the Second IMO GHG Study 2009 (x-axis) and the Third IMO GHG Study 2014 (y-axis)
Table 33 summarizes this discussion by making explicit the key differences between the 2009 study and
the current study. Given these observations, the general conclusion is that better AIS data on activity are
determinants of the precision of individual vessel calculations for activity-based emissions inventories. The
variation between vessel voyage days, vessels in a vessel category and other important variations can only be
evaluated with access to very detailed activity data. However, if a more general approach uses representative
input parameters that reflect the best composite activity data, the results will generally be similar.
Table 33 – Summary of major differences between the Second IMO GHG Study 2009
and Third IMO GHG Study 2014
Key variable Differences 2009 study 2014 study Overall effect
Days at sea Data and method Annual IHSF status
indicator only
At-sea main
engine MCR
Data and method
AIS-informed expert
judgement
Auxiliary engine Data and method Expert judgement
annual aggregates
Uses quarterly IHSF status indicator to
indicate if laid up for part of the year
Uses AIS data extrapolation, quality-checked
using LRIT and noon reports
Auxiliary power outputs derived from vessel
boarding data and applied according to
mode of operation
Minor decrease
in emissions
Minor increase
in emissions
Minor increase
in emissions