MnrAq

Inventories of CO2 emissions from international shipping 2007–2012 89
1.6 Comparison of the CO 2 inventories in this study
to the Second IMO GHG Study 2009 inventories
The Third IMO GHG Study 2014 produces multi-year inventories including 2007, which is the year that
the Second IMO GHG Study 2009 selected for its most detailed inventory. The two top-down inventories
compare very closely, at 249 million versus 234 million metric tonnes of fuel for the 2014 and 2009 studies
respectively. Top-down comparisons differ by less than 10% and can be explained by the extrapolation of
2005 IEA data used by the Second IMO GHG Study 2009 to estimate 2007 top-down totals. Similarly, the best
estimates for bottom-up global fuel inventories for 2007 in both studies differ by just over 5%, at 352 million
versus 333 million metric tonnes fuel respectively. Bottom-up fuel inventories for international shipping differ
by less than 3%.
Figure 65 and Figure 66 present results from this study (all years) and also from the Second IMO GHG Study
2009 (2007 only), including the uncertainty ranges for this work as presented in Section 1.5. The comparison
of the estimates in 2007 shows that for both the top-down and bottom-up analysis methods, for both the total
fuel inventory and international shipping, the results of the Third IMO GHG Study 2014 are in close agreement
with findings from the Second IMO GHG Study 2009. Similarly, the CO 2 estimate of 1,054 million metric
tonnes reported by the Second IMO GHG Study 2009 falls within the multi-year range of CO 2 estimates
reported in the bottom-up method for this study.
Figure 65: Top-down and bottom-up inventories for all ship fuels, from the Third IMO GHG Study 2014 and
the Second IMO GHG Study 2009