Third IMO Greenhouse Gas Study 2014

Scenarios for shipping emissions 2012–2050 145
Figure 88: Impact of productivity assumptions on emissions projections
There are other ways of increasing productivity than increasing the average cargo load. When demand
increases and the size of the fleet cannot keep up with the rising demand, a natural response is for ships to
increase their speed. This also increases productivity. However, since fuel use and emissions per tonne-mile
are roughly proportional to the square of the speed, a speed increase would result in emissions that are higher
than emissions at constant productivity.
In sum, our emissions projections are sensitive to our assumption that productivity will revert to its long-term
average value without increasing emissions per ship. If productivity remains constant (because ships will
continue to operate at their current load factors, with their current number of days at sea and at their current
speed), emissions are likely to be 10% higher than projected. If productivity increases because ships increase
their speed at sea, emissions are likely to increase by a higher amount.
3.3.5 Uncertainty
There are two sources of uncertainty in the scenarios. The first is that the estimates of emissions in the
base year have an uncertainty range, which has been discussed in Section 1.5. As our emissions projection
model calculated future emissions on the basis of base-year emissions and relative changes in parameters
(discussed in Section 3.2), uncertainty in the base year carries forward into future years. The second source of
uncertainty is that the future is, in itself, uncertain. This type of uncertainty is addressed by showing different
scenarios. While the scenarios are stylized representations of the future, and have no uncertainty of their own,
uncertainty is introduced by the fact that each of the BAU scenarios is equally likely to occur. Hence, on top
of the uncertainty in the base-year emissions, there is uncertainty in future developments that increases over
time.
3.4 Main results
Maritime emissions projections show an increase in fuel use and GHG emissions in the period up to 2050,
despite significant regulatory and market-driven improvements in efficiency. Depending on future economic
and energy developments, our BAU scenarios project an increase of 50%–250% in the period up to 2050.
Further action on efficiency and emissions can mitigate emissions growth, although all scenarios but one
project emissions in 2050 to be higher than in 2012. The main driver of the emissions increase is the projected
rise in demand for maritime transport. This rise is most pronounced in scenarios that combine the sustained
use of fossil fuels with high economic growth and is lower in scenarios that involve a transition to renewable
energy sources or a more moderate growth pattern.