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Annex 7 259
Figure 35 shows that future growth rates of TST can be successfully modelled in a non-linear fashion, which is
more realistic than the conventional linear model, by three different cargo types. This is a distinct advantage
for the next step of assembling a simplified modelling system of future emissions.
Sensitivities
Removing the period 1970–1985 from the total oil model results in an early maturation of total oil. However,
even when these data are included, despite the model not being as statistically robust, early maturation is still
shown. The weakest model is that of the total (non-coal) bulk dry goods, as the ratio to GDP is almost constant
over time, with only a weak linear or non-linear increase. However, while a linear model is statistically
significant, it does not indicate growth (in ratio) much different to that of the non-linear model. The ratio of
other dry cargoes also shows something of an excursion over the period 1970 to 1985; however, this is not
as easy to explain (in terms of physical events/changes in the underlying data) from known causes as is the
case for total oil. However, if this period is removed, the non-linear model indicates a growth in ratio twice
that of the model that includes the entire data series. Given that the explanation for this excursion is less easy
than that of total oil, a conservative approach has been adopted that includes the entire data series, resulting
in a lower ratio projection. However, it should be remembered that in the projections, the proxy data (i.e. oil,
coal consumption, GDP projections) are highly influential in the end ship traffic projections and, in the case
of GDP, tend to dominate the calculations.
Fleet productivity projections
For the emissions projection, the development of the tonnage of the different ship types is determined by
a projection of the productivity of the ships (highlighted red in the schematic presentation of the model
structure), defined as transport work per deadweight tonne.
Figure 36: The role of fleet productivity in the model structure
More precisely, the fleet is assumed to grow if, given the projected productivity, the expected transport
demand could not be met by the fleet. On the other hand, if, given the projected productivity, the expected
transport demand could be met by a smaller fleet, the active fleet is not assumed to decrease. That means