Third IMO Greenhouse Gas Study 2014

Scenarios for shipping emissions 2012–2050 143
in other scenarios the relative contributions of ship types will be different, all scenarios show a larger increase
in emissions from unitized cargo ships than from other ship types. While unitized cargo ships accounted for a
little over 40% of maritime transport CO 2 emissions in 2012, they are projected to account for 50% or more
by 2025 in all scenarios. In scenarios with a high economic growth, they are projected to account for two
thirds by 2045 or 2050.
Figure 87: Specific output for scenario 15 (RCP4.5, SSP3, low LNG/no additional ECA, low efficiency)
3.3.3 Results for other substances
Table 79 shows the projection of the emissions of other substances. For each year, the median, minimum
and maximum emissions are expressed as a share of their 2012 emissions. Most emissions increase in parallel
with CO 2 and fuel, with minor changes due to changes in the fuel mix. However, there are some notable
exceptions:
• Methane emissions are projected to increase rapidly (albeit from a very low base) as the share of LNG
in the fuel mix increases. In high ECA/high LNG scenarios, the increase is naturally higher than in the
constant ECA/low LNG scenarios.
• HFC emissions result from leakage of refrigerants and coolants and are a function of the number of
ships rather than of the amount of fuel used.
• Emissions of nitrogen oxides increase at a lower rate than CO 2 emissions as a result of the replacement
of old engines by Tier I and Tier II engines and the increasing share of LNG in the fuel mix. In addition,
the engines of new ships in ECAs will meet Tier III requirements, so scenarios that assume an increase
in the share of fuel used in ECAs show a slower increase in NO x emissions or in some scenarios a
decrease.
• Emissions of sulphurous oxides and PM emissions also increase at a lower rate than CO 2 emissions.
This is driven by MARPOL Annex VI requirements on the sulphur content of fuels (which also impact
PM emissions). In scenarios that assume an increase in the share of fuel used in ECAs, the impact of
these regulations is stronger.