55most recent IPCC report (Rogelj et al. 2016 ), below we show these GCMs likely
over-estimate the actual warming that will occur in the coming decades.
Figure 2.3 shows projections of ΔT from the CMIP5 GCMs found using RCP 4.5
and RCP 8.5. Observations of ΔT from CRU, NCEI, and GISS up to year 2012, as
well as the CRU estimate of the uncertainty on ΔT, are shown. The green hatched
trapezoid in Fig. 2.3 is the “indicative likely range for annual mean ΔT” provided
by Chap. 11 of IPCC ( 2013 ).^7 Section 11.3.6.3 of this report states:
some CMIP5 models have a higher transient response to GHGs and a larger response to other
anthropogenic forcings (dominated by the effects of aerosols) than the real world (medium
confidence). These models may warm too rapidly as GHGs increase and aerosols decline(^7) The trapezoid also appears in Fig. TS.14, p. 87, of the IPCC ( 2013 ) Technical Summary.
CRU, GISS, & NCEI w/ unc
CMIP5 (41 models)
IPCC likely range
CRU, GISS, & NCEI w/ unc
CMIP5 (38 models)
IPCC likely range
RCP 4.5
RCP 8.5
Fig. 2.3 Observed and GCM simulated global warming. (a) Time series of global, annually aver-
aged ΔT relative to pre-industrial baseline from 41 GCMs that submitted output to the CMIP5
archive covering both historical and future time periods, using RCP4.5 (light blue). The maximum
and minimum values of CMIP5 ΔT are indicated by the dark blue dashed lines, while the multi-
model- mean is denoted by the dark blue solid line. Also shown are global, annually averaged
observed ΔT from CRU, GISS, and NCEI (black) along with error bars (grey) that represent the
uncertainty on the CRU time series. The green trapezoid represents the indicative likely range for
annual average ΔT for 2016–2035 (i.e., top and bottom of trapezoid are upper and lower limits,
respectively) and the green bar represents the likely range for the mean value of ΔT over 2006 to
2035, both given in Chap. 11 of IPCC ( 2013 ); (b) same as (a), expect for 38 GCMs that submitted
output to the CMIP5 archive covering both historical and future time periods using RCP8.5 (red).
After Fig. 11.25a and 11.25b of (IPCC 2013 ). See Methods for further information
2.1 Introduction