<s>
A	O
general	B-Application
circulation	I-Application
model	I-Application
(	O
GCM	O
)	O
is	O
a	O
type	O
of	O
climate	B-Application
model	I-Application
.	O
</s>
<s>
Atmospheric	O
and	O
oceanic	O
GCMs	O
(	O
AGCM	B-Application
and	O
OGCM	B-Application
)	O
are	O
key	O
components	O
along	O
with	O
sea	O
ice	O
and	O
land-surface	O
components	O
.	O
</s>
<s>
GCMs	O
and	O
global	B-Application
climate	I-Application
models	I-Application
are	O
used	O
for	O
weather	O
forecasting	O
,	O
understanding	O
the	O
climate	O
,	O
and	O
forecasting	O
climate	O
change	O
.	O
</s>
<s>
The	O
acronym	O
GCM	O
originally	O
stood	O
for	O
General	B-Application
Circulation	I-Application
Model	I-Application
.	O
</s>
<s>
Recently	O
,	O
a	O
second	O
meaning	O
came	O
into	O
use	O
,	O
namely	O
Global	B-Application
Climate	I-Application
Model	I-Application
.	O
</s>
<s>
While	O
these	O
do	O
not	O
refer	O
to	O
the	O
same	O
thing	O
,	O
General	B-Application
Circulation	I-Application
Models	I-Application
are	O
typically	O
the	O
tools	O
used	O
for	O
modelling	B-Application
climate	I-Application
,	O
and	O
hence	O
the	O
two	O
terms	O
are	O
sometimes	O
used	O
interchangeably	O
.	O
</s>
<s>
However	O
,	O
the	O
term	O
"	O
global	B-Application
climate	I-Application
model	I-Application
"	O
is	O
ambiguous	O
and	O
may	O
refer	O
to	O
an	O
integrated	O
framework	O
that	O
incorporates	O
multiple	O
components	O
including	O
a	O
general	B-Application
circulation	I-Application
model	I-Application
,	O
or	O
may	O
refer	O
to	O
the	O
general	O
class	O
of	O
climate	B-Application
models	I-Application
that	O
use	O
a	O
variety	O
of	O
means	O
to	O
represent	O
the	O
climate	O
mathematically	O
.	O
</s>
<s>
It	O
became	O
the	O
first	O
successful	O
climate	B-Application
model	I-Application
.	O
</s>
<s>
Later	O
the	O
Hadley	O
Centre	O
for	O
Climate	O
Prediction	O
and	O
Research	O
's	O
HadCM3	B-Application
model	O
coupled	O
ocean-atmosphere	O
elements	O
.	O
</s>
<s>
Atmospheric	O
(	O
AGCMs	B-Application
)	O
and	O
oceanic	O
GCMs	O
(	O
OGCMs	B-Application
)	O
can	O
be	O
coupled	O
to	O
form	O
an	O
atmosphere-ocean	O
coupled	O
general	B-Application
circulation	I-Application
model	I-Application
(	O
CGCM	O
or	O
AOGCM	B-Application
)	O
.	O
</s>
<s>
With	O
the	O
addition	O
of	O
submodels	O
such	O
as	O
a	O
sea	O
ice	O
model	O
or	O
a	O
model	O
for	O
evapotranspiration	O
over	O
land	O
,	O
AOGCMs	B-Application
become	O
the	O
basis	O
for	O
a	O
full	O
climate	B-Application
model	I-Application
.	O
</s>
<s>
A	O
simple	O
general	B-Application
circulation	I-Application
model	I-Application
(	O
SGCM	O
)	O
consists	O
of	O
a	O
dynamic	O
core	O
that	O
relates	O
properties	O
such	O
as	O
temperature	O
to	O
others	O
such	O
as	O
pressure	O
and	O
velocity	O
.	O
</s>
<s>
Atmospheric	O
GCMs	O
(	O
AGCMs	B-Application
)	O
model	O
the	O
atmosphere	O
(	O
and	O
typically	O
contain	O
a	O
land-surface	O
model	O
as	O
well	O
)	O
using	O
imposed	O
sea	O
surface	O
temperatures	O
(	O
SSTs	O
)	O
.	O
</s>
<s>
AGCMs	B-Application
consist	O
of	O
a	O
dynamical	O
core	O
which	O
integrates	O
the	O
equations	O
of	O
fluid	O
motion	O
,	O
typically	O
for	O
:	O
</s>
<s>
parameters	B-Application
for	O
:	O
</s>
<s>
OGCMs	B-Application
model	O
the	O
ocean	O
(	O
with	O
fluxes	O
from	O
the	O
atmosphere	O
imposed	O
)	O
and	O
may	O
contain	O
a	O
sea	O
ice	O
model	O
.	O
</s>
<s>
AOGCMs	B-Application
(	O
e.g.	O
</s>
<s>
HadCM3	B-Application
,	O
GFDL	B-Application
CM2.X	I-Application
)	O
combine	O
the	O
two	O
submodels	O
.	O
</s>
<s>
AOGCMs	B-Application
internalise	O
as	O
many	O
processes	O
as	O
possible	O
.	O
</s>
<s>
While	O
the	O
simpler	O
models	O
are	O
generally	O
susceptible	O
to	O
analysis	O
and	O
their	O
results	O
are	O
easier	O
to	O
understand	O
,	O
AOGCMs	B-Application
may	O
be	O
nearly	O
as	O
hard	O
to	O
analyse	O
as	O
the	O
climate	O
itself	O
.	O
</s>
<s>
The	O
fluid	O
equations	O
for	O
AGCMs	B-Application
are	O
made	O
discrete	O
using	O
either	O
the	O
finite	B-Algorithm
difference	I-Algorithm
method	I-Algorithm
or	O
the	O
spectral	B-Algorithm
method	I-Algorithm
.	O
</s>
<s>
Typical	O
AGCM	B-Application
resolutions	O
are	O
between	O
1	O
and	O
5	O
degrees	O
in	O
latitude	O
or	O
longitude	O
:	O
HadCM3	B-Application
,	O
for	O
example	O
,	O
uses	O
3.75	O
in	O
longitude	O
and	O
2.5	O
degrees	O
in	O
latitude	O
,	O
giving	O
a	O
grid	O
of	O
96	O
by	O
73	O
points	O
(	O
96	O
x	O
72	O
for	O
some	O
variables	O
)	O
;	O
and	O
has	O
19	O
vertical	O
levels	O
.	O
</s>
<s>
Ocean	O
resolutions	O
tend	O
to	O
be	O
higher	O
,	O
for	O
example	O
HadCM3	B-Application
has	O
6	O
ocean	O
grid	O
points	O
per	O
atmospheric	O
grid	O
point	O
in	O
the	O
horizontal	O
.	O
</s>
<s>
This	O
would	O
lead	O
to	O
computational	O
instabilities	O
(	O
see	O
CFL	B-Algorithm
condition	I-Algorithm
)	O
and	O
so	O
the	O
model	O
variables	O
must	O
be	O
filtered	O
along	O
lines	O
of	O
latitude	O
close	O
to	O
the	O
poles	O
.	O
</s>
<s>
Some	O
experiments	O
use	O
geodesic	B-Application
grids	I-Application
and	O
icosahedral	O
grids	O
,	O
which	O
(	O
being	O
more	O
uniform	O
)	O
do	O
not	O
have	O
pole-problems	O
.	O
</s>
<s>
Another	O
approach	O
to	O
solving	O
the	O
grid	O
spacing	O
problem	O
is	O
to	O
deform	O
a	O
Cartesian	O
cube	B-Application
such	O
that	O
it	O
covers	O
the	O
surface	O
of	O
a	O
sphere	O
.	O
</s>
<s>
Some	O
early	O
versions	O
of	O
AOGCMs	B-Application
required	O
an	O
ad	O
hoc	O
process	O
of	O
"	O
flux	O
correction	O
"	O
to	O
achieve	O
a	O
stable	O
climate	O
.	O
</s>
<s>
Convection	O
occurs	O
on	O
too	O
small	O
a	O
scale	O
to	O
be	O
resolved	O
by	O
climate	B-Application
models	I-Application
,	O
and	O
hence	O
it	O
must	O
be	O
handled	O
via	O
parameters	B-Application
.	O
</s>
<s>
Coupled	O
AOGCMs	B-Application
use	O
transient	B-Application
climate	I-Application
simulations	I-Application
to	O
project/predict	O
climate	O
changes	O
under	O
various	O
scenarios	O
.	O
</s>
<s>
For	O
the	O
7	O
climate	B-Application
models	I-Application
shown	O
there	O
,	O
the	O
temperature	O
change	O
to	O
2100	O
varies	O
from	O
2	O
to	O
4.5	O
°C	O
with	O
a	O
median	O
of	O
about	O
3°C	O
.	O
</s>
<s>
AOGCMs	B-Application
internalise	O
as	O
many	O
processes	O
as	O
are	O
sufficiently	O
understood	O
.	O
</s>
<s>
A	O
debate	O
over	O
how	O
to	O
reconcile	O
climate	B-Application
model	I-Application
predictions	O
that	O
upper	O
air	O
(	O
tropospheric	O
)	O
warming	O
should	O
be	O
greater	O
than	O
observed	O
surface	O
warming	O
,	O
some	O
of	O
which	O
appeared	O
to	O
show	O
otherwise	O
,	O
was	O
resolved	O
in	O
favour	O
of	O
the	O
models	O
,	O
following	O
data	O
revisions	O
.	O
</s>
<s>
Cloud	O
effects	O
are	O
a	O
significant	O
area	O
of	O
uncertainty	O
in	O
climate	B-Application
models	I-Application
.	O
</s>
<s>
Climate	O
researchers	O
around	O
the	O
world	O
use	O
climate	B-Application
models	I-Application
to	O
understand	O
the	O
climate	O
system	O
.	O
</s>
<s>
The	O
precise	O
magnitude	O
of	O
future	O
changes	O
in	O
climate	O
is	O
still	O
uncertain	O
;	O
for	O
the	O
end	O
of	O
the	O
21st	O
century	O
(	O
2071	O
to	O
2100	O
)	O
,	O
for	O
SRES	O
scenario	O
A2	O
,	O
the	O
change	O
of	O
global	O
average	O
SAT	O
change	O
from	O
AOGCMs	B-Application
compared	O
with	O
1961	O
to	O
1990	O
is	O
+	O
3.0	O
°C	O
(	O
5.4	O
°F	O
)	O
and	O
the	O
range	O
is	O
+	O
1.3	O
to	O
+	O
4.5	O
°C	O
( +	O
2.3	O
to	O
8.1	O
°F	O
)	O
.	O
</s>
<s>
However	O
,	O
the	O
report	O
also	O
observed	O
that	O
the	O
rate	O
of	O
warming	O
over	O
the	O
period	O
1998	O
–	O
2012	O
was	O
lower	O
than	O
that	O
predicted	O
by	O
111	O
out	O
of	O
114	O
Coupled	B-Application
Model	I-Application
Intercomparison	I-Application
Project	I-Application
climate	B-Application
models	I-Application
.	O
</s>
<s>
The	O
global	B-Application
climate	I-Application
models	I-Application
used	O
for	O
climate	O
projections	O
are	O
similar	O
in	O
structure	O
to	O
(	O
and	O
often	O
share	O
computer	O
code	O
with	O
)	O
numerical	B-General_Concept
models	I-General_Concept
for	I-General_Concept
weather	I-General_Concept
prediction	I-General_Concept
,	O
but	O
are	O
nonetheless	O
logically	O
distinct	O
.	O
</s>
<s>
Currently	O
the	O
ECMWF	O
runs	O
at	O
resolution	O
as	O
opposed	O
to	O
the	O
scale	O
used	O
by	O
typical	O
climate	B-Application
model	I-Application
runs	O
.	O
</s>
<s>
Like	O
most	O
global	O
numerical	B-General_Concept
weather	I-General_Concept
prediction	I-General_Concept
models	O
such	O
as	O
the	O
GFS	O
,	O
global	B-Application
climate	I-Application
models	I-Application
are	O
often	O
spectral	O
models	O
instead	O
of	O
grid	O
models	O
.	O
</s>
<s>
Climate	B-Application
models	I-Application
use	O
quantitative	O
methods	O
to	O
simulate	O
the	O
interactions	O
of	O
the	O
atmosphere	O
,	O
oceans	O
,	O
land	O
surface	O
and	O
ice	O
.	O
</s>
<s>
All	O
climate	B-Application
models	I-Application
take	O
account	O
of	O
incoming	O
energy	O
as	O
short	O
wave	O
electromagnetic	O
radiation	O
,	O
chiefly	O
visible	O
and	O
short-wave	O
(	O
near	O
)	O
infrared	O
,	O
as	O
well	O
as	O
outgoing	O
energy	O
as	O
long	O
wave	O
(	O
far	O
)	O
infrared	O
electromagnetic	O
radiation	O
from	O
the	O
earth	O
.	O
</s>
<s>
Atmospheric	O
GCMs	O
(	O
AGCMs	B-Application
)	O
model	O
the	O
atmosphere	O
and	O
impose	O
sea	O
surface	O
temperatures	O
as	O
boundary	O
conditions	O
.	O
</s>
<s>
Coupled	O
atmosphere-ocean	O
GCMs	O
(	O
AOGCMs	B-Application
,	O
e.g.	O
</s>
<s>
HadCM3	B-Application
,	O
EdGCM	O
,	O
GFDL	B-Application
CM2.X	I-Application
,	O
ARPEGE-Climat	O
)	O
combine	O
the	O
two	O
models	O
.	O
</s>
<s>
Finally	O
,	O
(	O
coupled	O
)	O
atmosphere	O
–	O
ocean	O
–	O
sea	O
ice	O
global	B-Application
climate	I-Application
models	I-Application
discretise	O
and	O
solve	O
the	O
full	O
equations	O
for	O
mass	O
and	O
energy	O
transfer	O
and	O
radiant	O
exchange	O
.	O
</s>
