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3
Scenarios for shipping emissions
2012–2050
3.1 Introduction
This chapter presents emissions scenarios for all six GHGs (CO 2 , CH 4 , N 2 O, HFCs, PFCs, SF 6 ) and for other
relevant substances as defined in this study (NO x , NMVOC, CO, PM, SO x ).
Emissions scenarios present possible ways in which emissions could develop, building on plausible
socioeconomic, energy and policy scenarios. The emissions scenarios can inform policymakers, scientists
and other stakeholders about the development of the environmental impacts of shipping, its drivers and the
relevance of possible policy instruments to address emissions.
3.1.1 Similarities with and differences from Second IMO GHG Study 2009
The emissions scenarios have been developed using a similar approach to that of the Second IMO GHG
Study 2009, i.e. by modelling the most important drivers of maritime transport and efficiency trends in order
to project energy demand in the sector. For most emissions, the energy demand is then multiplied by an
emissions factor to arrive at an emissions projection. More detail about the methods and modelling can be
found in Section 3.2.
Even though the approach is similar, the methods have been improved in important ways, taking into account
advances in the literature and newly developed scenarios. Some of the most important improvements are
highlighted below.
Socioeconomic and energy scenarios
In the Second IMO GHG Study 2009, a range of transport and corresponding emissions projections to 2050
were presented. The underlying overall basis for these projections were the IPCC Special Report on Emissions
Scenarios (SRES) (based upon the IPCC 2000 SRES, which were widely in use at the time). There has been
increased recognition across the climate-scenario-modelling community that there is a need for an updated
set of scenarios, but also recognition of the need to circumvent the time and expense associated with another
IPCC-focused exercise. Thus, the relevant community itself developed the concept of RCPs. Since these are
now in use across the climate community, they have been adopted for this study (see Section 3.2.2). Outside
the climate research community, other long-term scenarios exist (e.g. IEA, 2013; OECD, 2012; IMF, 2014; RTI,
2013).
Previously, shipping emissions scenarios were based more loosely on a consortium consensus approach,
the so-called Delphi method. This study adopts a more disaggregated numerical approach with explicit
improvements to the projection methodology by splitting the projections by ship type, using a non-linear
regression model of a type widely adopted in the econometric literature (as opposed to simple linear models),
and decoupling the transport of fossil fuels from GDP. In the previous report, there was no such discrimination
by type, or consideration of future worlds where fossil fuel energy demand is decoupled from GDP. More
details are provided in Section 3.2.2 and Annex 7.