Third IMO Greenhouse Gas Study 2014
GHG3%20Executive%20Summary%20and%20Report
GHG3%20Executive%20Summary%20and%20Report
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130 <strong>Third</strong> <strong>IMO</strong> GHG <strong>Study</strong> <strong>2014</strong><br />
A useful summary and guide to the origin and formulation of the RCP scenarios is provided by Wayne (2013).<br />
The “concentration” refers to that of CO 2 and the “pathways” are “representative” of possible outcomes of<br />
energy, population, policy and other drivers that will ultimately determine the concentration of CO 2 in the<br />
atmosphere. There are four main RCPs in use, detailed in Table 69.<br />
Table 69 – Descriptions and sources of representative concentration pathways<br />
RCP Description Source references Model<br />
RCP2.6 (or 3PD) Peak in radiative forcing at ~3 W/m 2 before 2100<br />
and decline<br />
RCP4.5<br />
RCP6.0<br />
RCP8.5<br />
Stabilization without overshoot pathway to<br />
4.5 W/m 2 at stabilization after 2100<br />
Stabilization without overshoot pathway to<br />
6 W/m 2 at stabilization after 2100<br />
Rising radiative forcing pathway leading to<br />
8.5 W/m 2 in 2100.<br />
Van Vuuren et al., 2006, 2007<br />
Clarke et al., 2007; Wise et al., 2009<br />
Hijoka et al., 2008<br />
Riahi et al., 2007<br />
IMAGE<br />
GCAM<br />
AIM<br />
MESSAGE<br />
The numbers associated with the RCPs (2.6–8.5) simply refer to resultant radiative forcing in W/m 2 by 2100.<br />
Further technical details of the RCPs are given in Moss et al. (2010). The RCPs cover a range of ultimate<br />
temperature projections by 2100 (i.e. global mean surface temperature increases over the pre-industrial period<br />
from GHGs), from around 4.9 °C (RCP8.5) to 1.5 °C in the most optimistic scenario (RCP2.6 or RCP3PD, where<br />
PD refers to peak and decline).<br />
These RCPs are used to project shipping coal and liquid fossil fuel transport work, on the basis of a historical<br />
correlation with global coal and oil consumption (see Section 3.2.3), using the IAM energy demand projections<br />
of different fuel/energy types (EJ/yr). A set of GDP projections from the associated five SSP scenarios (see<br />
Kriegler et al., 2012) was used for non-fossil-fuel transport projections (see Section 3.2.3).<br />
The five SSPs each have different narratives (Ebi et al., 2013) and are summarized in Table 70.<br />
Table 70 – Short narratives of shared socioeconomic pathways<br />
SSP number and name<br />
SSP1: Sustainability<br />
SSP2: Middle of the road<br />
SSP3: Fragmentation<br />
SSP4: Inequality<br />
SSP5: Conventional<br />
development<br />
Short narrative<br />
A world making relatively good progress towards sustainability, with ongoing efforts to achieve<br />
development goals while reducing resource intensity and fossil fuel dependency. It is an<br />
environmentally aware world with rapid technology development and strong economic growth,<br />
even in low-income countries.<br />
A world that sees the trends typical of recent decades continuing, with some progress towards<br />
achieving development goals. Dependency on fossil fuels is slowly decreasing. Development of<br />
low-income countries proceeds unevenly.<br />
A world that is separated into regions characterized by extreme poverty, pockets of moderate<br />
wealth and a large number of countries struggling to maintain living standards for a rapidly<br />
growing population.<br />
A highly unequal world in which a relatively small, rich global elite is responsible for most<br />
GHG emissions, while a larger, poor group that is vulnerable to the impact of climate changes<br />
contributes little to the harmful emissions. Mitigation efforts are low and adaptation is difficult<br />
due to ineffective institutions and the low income of the large poor population.<br />
A world in which development is oriented towards economic growth as the solution to<br />
social and economic problems. Rapid conventional development leads to an energy system<br />
dominated by fossil fuels, resulting in high GHG emissions and challenges to mitigation.<br />
This presented the problem of how to combine the RCPs with the SSPs and guidance was taken from Kriegler<br />
et al. (2012), as follows.<br />
In principle, several SSPs can result in the same RCP, so in theory many BAU scenarios can be developed.<br />
However, in order to limit the number of scenarios, while still showing the variety in possible outcomes, it<br />
was decided to combine each SSP with one RCP, under the constraint that this combination is feasible. The<br />
SSPs are thus aligned with the RCPs on the basis of their baseline warming. Increased mitigation effort would<br />
potentially result in less fossil fuel transport, probably somewhat lower economic growth until 2050 and<br />
therefore probably lower transport demand and maritime emissions.