Geoscience Reference
In-Depth Information
P
2080−2100
− P
1985−2005
12
11
GPCP v2.2
Historical
RCP 4.5
RCP 8.5
RCP 4.5 − Historical
RCP 8.5 − Historical
10
7
10
9
8
8
9
2
7
6
5
3
6
4
1
7
10
8
4
5
5
9
2
4
4
2
6
10
1
3
3
8
0
2
6
1
−2
(a)
(b)
0
0
1
2
3
4
5
6
1950
2000
2050
2100
Year
Global mean T difference (K)
Fig. 2 a Changes in global mean precipitation (relative to 1988-2005) for CMIP5 climate simulations
(RCP4.5 and RCP8.5 future projections relative to the parent simulation from the historical simulations,
models 1-10 in Table
2
). Observationally based GPCP precipitation anomalies are plotted for comparison.
Twenty-four month running means are applied. b 2080-2100 minus 1985-2005 global mean precipitation
change plotted relative to changes in global mean surface temperature for RCP4.5-historical and RCP8.5-
historical simulations. Model numbers in Table
2
are displayed, and a line of best fit to these values is shown
in black
and therefore increase P through the slow response term in (
2
). However, the relationship
between DT and DP is not robust, particularly for the RCP8.5 scenario; this may be
explained by the fact that the RCP8.5 scenario is far from equilibrium by 2100 (e.g.,
McInerney and Moyer
2012
), while the model simulations in the RCP4.5 scenario are
showing signs of a levelling off in DP (as DF
!
4
:
5Wm
2
after *2060). The INMCM4
model simulates a muted DP
=
DT response relative to other models, while the IPSL-
CM5A-LR and MRI-CGCM3 models simulate a slightly larger DP
=
DT response relative to
the other models (see Table
2
for definition of climate models). As noted, the actual DP is
also related to the direct influence of the radiative forcings upon atmospheric radiative
cooling (Andrews et al.
2010
) while the timescale for change in DT is lengthened for
models with weaker ocean heat uptake and more positive feedback (e.g., Hansen et al.
2011
). The contribution of natural variability, model diversity and scenario uncertainty to
precipitation projections is discussed further, in the context of the older CMIP3 model
simulations, by Hawkins and Sutton (
2011
)
To investigate the direct influence of radiative forcing on transient climate change, a
present-day AMIP5 simulation (observed sea surface temperature, SST, and sea ice distri-
bution are prescribed over the period 1979-2008) of the atmospheric component of the
