Geoscience Reference
In-Depth Information
Table 2
Details of CMIP5 climate models simulations employed
Modelling centre
Model
References
(1) Beijing Climate Center
BCC-CSM1-1
Wu et al. (
2012
)
(2) Canadian Centre for Climate Modelling
and Analysis
CanESM2 CanAM4
Arora et al. (
2011
)
(3) National Center for Atmospheric Research, USA
CCSM4
Gent et al. (
2011
)
(4) Centre National de Recherches
Meteorologiques, France
CNRM-CM5
Voldoire et al. (
2012
)
(5) Met Office Hadley Centre, UK
HadGEM2-ES
HadGEM2-A
Collins et al. (
2011
)
(6) Institute for Numerical Mathematics, Russia
INMCM4
Volodin et al. (
2010
)
(7) Institut Pierre Simon Laplace, France
IPSL-CM5A-LR
Hourdin et al. (
2012
)
(8) Max Planck Institute for Meteorology, Germany
MPI-ESM-LR
Raddatz et al. (
2007
)
(9) Meteorological Research Institute, Japan
MRI-CGCM3
Yukimoto et al. (
2012
)
(10) Norwegian Climate Centre
NorESM1-M
Zhang et al. (
2012
)
(11) Model for Interdisciplinary Research on
Climate, Japan
MIROC5
Watanabe et al. (
2010
)
Hadley Centre Global Environment Model version 2 (HadGEM2) model (Collins et al.
2011
) is conducted. A standard Atmospheric Models Intercomparison Project (AMIP5)
control run is used (CTL), in which realistic radiative forcings are prescribed, and compared
with an identical simulation but with greenhouse gases fixed at their 1978 levels (fGHG).
Figure
3
a shows declining CTL minus fGHG global mean clear-sky outgoing longwave
radiation, OLRc (dOLRc/dt =-0.37 W m
-2
/dec, r =-0.79). This is explained by the
rising greenhouse gas concentrations in CTL (e.g., Allan
2006
; Chung and Soden
2010
)
which reduce the longwave radiative cooling of the atmosphere to space. A decreasing
trend in total (all-sky) atmospheric net radiative cooling to space and to the surface
(Fig.
3
b) is less marked (dQ
atm
/dt =-0.13 W m
-2
/dec, r =-0.32) since the presence of
high-altitude cloud masks the enhanced greenhouse effect of rising CO
2
concentrations in
CTL. There are also substantial differences associated with differing internal variability
between experiments; this also explains most of the differences in P between CTL and
fGHG (Fig.
3
c), but a declining trend is also discernible (dP/dt =-0.15 %/dec *-
0.14 W m
-2
/dec, r =-0.25). The clear correlation between DQ
atm
and DP (r = 0.66) is
physically reasonable and primarily explained by internal variability differences between
simulations with only a small, yet detectable, fraction relating to the CO
2
trend.
(
a
)
(b
)
(
c
)
Fig. 3 Global mean differences in a clear-sky outgoing longwave radiation (OLR), b net all-sky
atmospheric radiative cooling and c precipitation for HadGEM2-A AMIP5 simulations with observed
greenhouse gases (CTL) and fixed greenhouse gases (fGHG) with least squares fit trend lines. A 3-month
box-car average is applied to the time series
