MnrAq

Inventories of CO2 emissions from international shipping 2007–2012 91
a) Deadweight tonnes b) Gross registered tonnes
c) Main engine power installed
Figure 67: Crossplots of deadweight tonnes, gross tonnes and average installed main engine power
for the year 2007, as reported by the Second IMO GHG Study 2009 (x-axis)
and the Third IMO GHG Study 2014 (y-axis)
There are differences in parameters between the studies. The most important uncertainty identified by the
Second IMO GHG Study 2009 was engine operating days, especially for main engines. The 2009 study
considered confidence to be “moderate, but dominat[ing] uncertainty”, and explained that the coverage
accuracy of the AIS data would affect uncertainty in several ways. Uncertainty in main engine load was
reported as the second most important parameter affecting confidence in the 2009 bottom-up calculations.
Generally, uncertainty in auxiliary engine inputs was assessed as moderate to low in the Second IMO GHG
Study 2009 (i.e. the study reported confidence in these to be moderate to high). The 2009 study identified
several ways in which auxiliary engine information was uncertain, including engine size, auxiliary engine
operating days, auxiliary engine load and auxiliary engine specific fuel oil consumption. The IHSF data on
auxiliary engines used in the Third IMO GHG Study 2014 remained sparse, although the consortium was able
to access auxiliary data for more than 1,000 ships from noon reports, previous vessel boardings, etc. These
are shown in Figure 68.