Paris Climate Agreement Beacon of Hope

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RCP 8.5. The colors represent the probability of a particular future value of ΔT
being achieved, for projections computed in the EM-GC framework weighted by 1/
χ^2. Essentially, the red (warm), white (mid-point), and blue (cool) colors represent
the visualization of a succession of histograms like those shown in Figs. 2.17 and
2.18. The GCM CMIP5 projections of ΔT (minimum, maximum, and multi-model
mean) for RCP 4.5 and RCP 8.5 are shown by the three grey lines. These lines,
identical to those shown in Fig. 2.3a (RCP 4.5) and Fig. 2.3b (RCP 8.5), are based
on our analysis of GCM output preserved on the CMIP5 archive. The green trape-
zoid, which originates from Fig. 11.25b of IPCC ( 2013 ), makes a final and rather

Table 2.1 Cumulative probability the rise in ΔT remains below a specific value, 2060 and 2100

2060 2100

1.5 °C 2.0 °C 1.5 °C 2.0 °C

CMIP5 GCMs RCP 4.5 0.027 0.270 0.0 0.206

CMIP5 GCMs RCP 8.5 0.0 0.026 0.0 0.0

EM-GC, RCP 4.5 0.787 0.995 0.751 0.989

EM-GC, RCP 8.5 0.215 0.816 0.0 0.098

Fig. 2.19 Global warming projections, RCP 4.5. Simulations of the GMST anomaly relative to
pre-industrial baseline (ΔT), found using the EM-GC (red, white, and blue colors) and from the
CMIP5 GCMs (grey lines). Observed ΔT from CRU is also shown (orange). All simulations
extend back to 1860; the figure shows ΔT from 1945 to 2100 so that the projections can be better
visualized. The green trapezoid shows the indicative likely range of annual average ΔT for 2016
to 2035 (roof and base of trapezoid are upper and lower limits) and the green bar indicates the
likely range of the mean value of ΔT over 2006 to 2035, both given in Chap. 11 of IPCC ( 2013 ).
The Paris Climate Agreement target and upper limit of 1.5 and 2.0 °C warming are denoted at the
end of the century. The three CMIP5 lines represent the minimum, maximum, and multi-model
mean of ΔT from the 41 GCMs that submitted projections for RCP 4.5 to the CMIP5 archive. The
EM-GC projections represent the probability that future value of ΔT will rise to the indicated level.
As for Fig. 2.17, EM-GC projections consider only acceptable fits to the climate record, are based
on the average of OHC from six data records, and have been weighted by 1/χ^2 prior to calculation
of the probabilities. The white patch of the red, white, and blue projection is the most probable
future value of ΔT found using this approach

2.5 Future Temperature Projections

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