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244 Third IMO GHG Study 2014
Figure 31: Uncertainty around the annual emissions (x-axis is ‘00,000 tonnes of CO 2 ;
y-axis is frequency) from a Monte Carlo simulation of an “average”
Panamax bulk carrier (60,000–99,999 dwt capacity) in 2012
Uncertainty in the aggregation of a fleet of ships’ emissions
Activity for ships that are in service but not observed in AIS is imputed. Epistemic and aleatory uncertainty
is introduced because the observed activity is propagated to the ships where imputed activity is used. The
assumptions used to estimate the influence of the uncertainty associated with the imputed fleet, in combination
with the uncertainty of the observed fleet, are listed in Table 20.
Table 20 – Estimated parameters for the uncertainty in the inputs
to the annual emissions calculation
Per annum per ship Input parameter Mean Standard deviation
A ship observed in AIS CO 2 emissions per year Read in from the per-year uncertainty analysis
A ship not observed in AIS
but identified as in service
Characteristics of an individual ship’s fuel consumption are
simulated from the distribution of the CO 2 emissions of the
observed fleet of the same ship type and size
The number of in-service ships is simulated as a uniform
distribution with a minimum value of zero (i.e. none of the
ships defined in IHSF as in service but not observed in AIS is
active), with the maximum given by the difference between
the size of the IHSF in-service fleet and the number of ships
observed on AIS in that type and size category
Results
Results are first calculated for each of the ship type and size categories and then aggregated to total uncertainty
characterizations for international shipping and for total shipping. The upper and lower bounds applied to the
Figures in Section 1.5.2 are obtained as the maximum and minimum values obtained from the Monte Carlo
simulation. The statistics of the outputs to that simulation can also be approximated as normal distributions
(similar to the uncertainties in the hourly aggregations), and Table 21 lists these for each of the ship type
and size categories. The variation in uncertainty between ship types and sizes can be seen, with the lowest