Third IMO Greenhouse Gas Study 2014

Scenarios for shipping emissions 2012–2050 129
this, combined with emissions factors (see Section 3.2.8), yields the emissions. Emissions are presented both
in aggregate and per ship type and size category.
A schematic presentation of the emissions projection model is shown in Figure 78.
3.2.2 Base scenarios
Figure 78: Schematic presentation of the emissions projection model
Scenario construction is necessary to gain a view of what may happen in the future. In the Second IMO GHG
Study 2009, background scenarios (SRES – see Section 3.1.1) were chosen from IPCC activities, since the 2009
study was primarily about emissions and it made sense to make the emissions scenarios consistent with other
associated climate projections. Here, this study basically follows the same logic; while other visions of the
future are available, and arguably equally plausible, since the overall subject of the present study is emissions,
this study follows the earlier precedent and uses approaches and assumptions that will ultimately allow the
projections to be used in climate studies. Moreover, data from climate projections studies include the essential
socioeconomic and energy drivers that are essential for the emissions projections made here.
After its Fourth Assessment Report, published in 2007, IPCC decided to update the projections to be used in
its next assessment report (AR5). The scenarios are called representative concentration pathways (RCPs). Their
naming and use are best explained in the quote below:
“The name ‘representative concentration pathways’ was chosen to emphasize the rationale behind their
use. RCPs are referred to as pathways in order to emphasize that their primary purpose is to provide
time-dependent projections of atmospheric greenhouse gas (GHG) concentrations. In addition, the term
pathway is meant to emphasize that it is not only a specific long-term concentration or radiative forcing
outcome, such as a stabilization level, that is of interest, but also the trajectory that is taken over time to
reach that outcome. They are representative in that they are one of several different scenarios that have
similar radiative forcing and emissions characteristics.” (Towards New Scenarios for Analysis of Emissions,
Climate Change, Impacts, and Response Strategies – IPCC Expert Meeting Report, 2007).