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Figure 2.4 is a so-called “ladder plot” that compares a time series of observed,
monthly values of ΔT (top rung) from CRU (black) to the output of the model (red).
For the simulation in Fig. 2.4, the AMV, PDO, and IOD terms have been neglected.
The model provides a reasonably good description of the observed global temperature
anomaly. The red curve on the top panel is the sum of the orange curve on the second
panel (total effect of human activity), the blue and purple curves on the third panel
(volcanic and solar terms), and the cardinal curve on the fourth panel (ENSO), plus the
Fig. 2.4 Observed and EM-GC simulated global warming, 1860–2015. Ladder plot showing CRU
observed global, monthly mean ΔT from CRU (black) and as simulated by the EM-GC (red), both
relative to pre-industrial baseline (top rung); the contribution to ΔT from humans (orange) (second
rung), and contributions from natural sources of climate variability due to fluctuations in the output
of the sun and major volcanic eruptions (third rung), and ENSO (fourth rung). The final rung com-
pares modeled and measured ocean heat content (OHC), where the data show the average (used in
the model) and standard deviation of OHC from six data sets. See Methods for further information
2 Forecasting Global Warming