88
century if the emissions of GHGs, particularly CO 2 , follow those used to drive RCP
8.5.^32 The book Six Degrees: Our Future on a Hotter Planet (Lynas 2008 ) provides
an accessible discourse of the consequences of global warming, organized into 1 °C
increments of future ΔT.
In the rest of this chapter, policy relevant projections of ΔT are shown, both from
the EM-GC framework and CMIP5 GCMs. Figures 2.17 shows the statistical distri-
bution of ΔT 2060 from our EM-GC calculations. The EM-GC based projections are
weighted by 1/χ^2 (i.e., the better the fit to the climate record, the more heavily a
particular projection is weighted). The height of each histogram represents the prob-
ability that a particular range of ΔT 2060 , defined by the width of each line segment,
(^32) As shown in Fig. 2.1, CO 2 and CH 4 reach alarmingly high levels at end of century in the RCP 8.5
scenario.
a
b
RCP 4.5
RCP 8.5
F
eedback
Pa
rameter
(W
m
-2
oC
-1
)
AerRF 2011 (Wm–2)
Fig. 2.16 Projected rise in GMST, year 2100, as a function of climate feedback and aerosol radia-
tive forcing. Same as Fig. 2.15, except for EM-GC projections out to year 2100. The same color
bar is used for both panels to accentuate the end of century difference between RCP 4.5 and RCP
8.5. The minimum and maximum values of ΔT 2100 are recorded on each panel
2 Forecasting Global Warming