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important appearance on these figures. Also, the Paris target (1.5 °C) and upper
limit (2 °C) are marked on the right vertical axis of both figures.
There are resounding policy implications inherent in Figs. 2.17, 2.18, 2.19, and
2.20. First, most importantly, and beyond debate of any reasonable quantitative analy-
sis of climate, if GHG emissions follow anything close to RCP 8.5, there is no chance
of achieving either the goal or upper limit of the Paris climate agreement (Fig. 2.20).
Even though there is a small amount of overlap between the Paris targets and our
EM-GC projections for year 2100 in Fig. 2.20, this is a false hope. In the highly
unlikely event this realization were to actually happen, it would just be a matter of
time before ΔT broke through the 2 °C barrier, with all of the attendant negative con-
sequences (Lynas 2008 ). Plus, of course, 1.5–2.0 °C warming (i.e., the lead up to
breaking the 2 °C barrier) could have rather severe consequences. This outcome is all
but guaranteed if GHG abundances follow that of RCP 8.5.
The second policy implication is that projections of ΔT found using the EM-GC
framework indicate that, if emissions of GHGs can be limited to those of RCP 4.5,
then by end-century there is:
(a) a 75 % probability the Paris target of 1.5 °C warming above pre-industrial will
be achieved
(b) a greater than 95 % probability the Paris upper limit of 2 °C warming will be
achieved
As will be shown in Chap. 3 , the cumulative effect of the commitments from nations
to restrict future emissions of GHGs, upon which the Paris Climate Agreement is
based, have the world on course to achieve GHG emissions that fall just below those
of RCP 4.5, provided: (1) both conditional and unconditional commitments are fol-
lowed; (2) reductions in GHG emissions needed to achieve the Paris agreement,
which generally terminate in 2030, are continually improved out to at least 2060.
Fig. 2.20 Global warming projections, RCP 8.5. Same as Fig. 2.19, except for the 38 GCMs that
submitted projections using RCP 8.5 to the CMIP5 archive. Note how the most probable evolution
of ΔT found using the EM-GC framework passes through the middle of the IPCC ( 2013 ) trape-
zoid, and is matched only by the lowest projection warmings of the CMIP5 GCMs
2 Forecasting Global Warming