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56 Third IMO GHG Study 2014
1.3.5 Shipping’s CO 2 e emissions
Carbon dioxide equivalency (CO 2 e) is a quantity that describes, for a given amount of GHG, the amount of
CO 2 that would have the same global warming potential (GWP) as another long-lived emitted substance,
when measured over a specified timescale (generally, 100 years). A total CO 2 e estimate is produced by
combining CO 2 emissions totals estimated in Section 1 with other GHG substances estimated in Section 2
and their associated GWP.
The Fifth IPCC Assessment Report (AR5) has changed the 100-year global warming potentials (GWP100)
from previous assessments because of new estimates of lifetimes, impulse response functions and radiative
efficiencies. IPCC (2013) acknowledges that the inclusion of indirect effects and feedbacks in metric values
has been inconsistent in IPCC reports, and therefore the GWPs presented in previous assessments may
underestimate the relative impacts of non-CO 2 gases.
The GWPs reported in IPCC (2013) include climate-carbon feedbacks for the reference gas CO 2 , and for the
non-CO 2 gases, GWPs are presented both with and without climate-carbon feedbacks. In accord with IPCC
(2013), such feedbacks may have significant impacts on metrics and should be treated consistently.
Using GWP100 with climate-carbon feedbacks, primary GHGs (CO 2 , N 2 O and CH 4 ) from shipping account
for approximately 961 million tonnes of CO 2 e in 2012. International shipping is estimated to account for
816 million tonnes of CO 2 e for primary GHGs in 2012.
Time series of bottom-up CO 2 e emissions estimates with climate-carbon feedbacks can be found in Table 18
and Table 19 and are presented in Figure 41.
Table 18 – Bottom-up CO 2 e emissions estimates with climate-carbon feedbacks
from total shipping (thousand tonnes)
2007 2008 2009 2010 2011 2012
CH 4 6,018 6,657 6,369 8,030 9,807 9,802
N 2 O 14,879 15,404 13,318 12,453 13,428 12,707
CO 2 1,100,100 1,135,100 977,900 914,700 1,021,600 938,100
Total 1,120,997 1,157,160 997,587 935,183 1,044,835 960,608
Table 19 – Bottom-up CO 2 e emissions estimates with climate-carbon feedbacks
from international shipping (thousand tonnes)
2007 2008 2009 2010 2011 2012
CH 4 5,929 6,568 6,323 7,969 9,740 9,742
N 2 O 12,152 12,689 11,860 10,615 11,437 10,931
CO 2 884,900 920,900 855,100 771,400 849,500 795,700
Total 902,981 940,157 873,284 789,983 870,678 816,372