Geoscience Reference
In-Depth Information
One class of scenarios includes idealized emis-
sions or concentration pathways to investigate
processes, feedbacks, timescales, and inertia in the
climate system. These scenarios are usually devel-
oped from a natural science perspective and used
for their illustrative power. Examples are a com-
plete instantaneous reduction of emissions at a
given year or idealized pathways leading to stabili-
zation of greenhouse gas concentrations (Schimel
et
al.
1997). Another class of emissions scenarios has
been developed using integrated assessment frame-
works and integrated assessment models (IAMs) by
considering plausible future demographic, social,
economic, technological, and environmental devel-
opments. Examples include the scenarios of the
IPCC SRES (Naki ´enovi ´
et al
. 2000) and the more
recently developed representative concentration
pathways (RCPs; Moss
et al.
2008 , 2010 ; Van Vuuren
et al.
2008a ).
The SRES emissions scenarios do not include
explicit climate change mitigation actions. Such sce-
narios are usually called baseline or reference sce-
narios. In this chapter, results based on the two
illustrative SRES scenarios B1 and A2, a low- and a
high-emissions baseline scenario, are discussed
(Fig. 14.1). The SRES scenarios have been widely
used in the literature and in the IPCC Fourth
Assessment Report. They are internally consistent
scenarios in the sense that each is based on a 'narra-
tive storyline' that describes the relationships
between the forces driving emissions. The 21st cen-
tury emissions of the major anthropogenic green-
house gases [CO
2
, CH
4
, N
2
O, halocarbons, and
sulphur hexal uoride (SF
6
)], aerosols and tropo-
spheric ozone precursors [sulphur dioxide (SO
2
),
carbon monoxide (CO), NO
x
, and volatile organic
compounds (VOCs)] are quantii ed with IAMs. The
extent of the technological improvements contained
in the SRES scenarios is not always appreciated.
The SRES scenarios include already large and
important improvements in energy intensity
(energy used per unit of gross domestic product)
and the deployment of non-carbon-emitting
energy supply technologies compared with the
present (Edmonds
et al.
2004). By the year 2100, the
primary energy demand in the SRES scenarios
ranges from 55% to more than 90% lower than had
no improvement in energy intensity occurred. In
addition, in many of the SRES scenarios the deploy-
ment of non-carbon-emitting energy supply sys-
tems (solar, wind, nuclear, and biomass) exceeds
the size of the global energy system in 1990.
2100
B(a)
B
1800
A2
B
B
1500
B
B(b)
B
1200
5.3
4.5
4.5
4.5
4.5
B1
4.5
900
4.5
4.5
4.0
3.7
3.5
600
2.9
3.2
2.6
300
0
AIM IPAC
IMAGE
MiniCam
EPPA MESSAGE
SRES
Figure 14.1
Cumulative CO
2
emissions in gigatonnes of carbon (Gt C) over the 21st century for a range of baseline (B; red), climate mitigation (blue), and
the SRES A2 and B1 (black) scenarios. The numbers related to the mitigation scenarios indicate the radiative forcing targets in W m
-2
imposed in the IAMs. The
labels below the columns refer to the IAMs used to quantify the scenarios (Weyant et al. 2006) and to the SRES scenarios (Nakic´enovic´ 2000), respectively.
