<s>
Radiative	B-Algorithm
forcing	I-Algorithm
(	O
or	O
climate	O
forcing	O
)	O
is	O
the	O
change	O
in	O
energy	O
flux	O
in	O
the	O
atmosphere	O
caused	O
by	O
natural	O
or	O
anthropogenic	O
factors	O
of	O
climate	O
change	O
as	O
measured	O
by	O
watts	O
/	O
meter²	O
.	O
</s>
<s>
Positive	O
radiative	B-Algorithm
forcing	I-Algorithm
means	O
Earth	O
receives	O
more	O
incoming	O
energy	O
from	O
sunlight	O
than	O
it	O
radiates	O
to	O
space	O
.	O
</s>
<s>
Conversely	O
,	O
negative	O
radiative	B-Algorithm
forcing	I-Algorithm
means	O
that	O
Earth	O
loses	O
more	O
energy	O
to	O
space	O
than	O
it	O
receives	O
from	O
the	O
Sun	O
,	O
which	O
produces	O
cooling	O
.	O
</s>
<s>
A	O
planet	O
in	O
radiative	O
equilibrium	O
with	O
its	O
parent	O
star	O
and	O
the	O
rest	O
of	O
space	O
can	O
be	O
characterized	O
by	O
net	O
zero	O
radiative	B-Algorithm
forcing	I-Algorithm
and	O
by	O
a	O
planetary	O
equilibrium	O
temperature	O
.	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
on	O
Earth	O
is	O
meaningfully	O
evaluated	O
at	O
the	O
tropopause	O
and	O
at	O
the	O
top	O
of	O
the	O
stratosphere	O
.	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
varies	O
with	O
solar	O
insolation	O
,	O
surface	O
albedo	O
,	O
and	O
the	O
atmospheric	O
concentrations	O
of	O
radiatively	O
active	O
gases	O
–	O
commonly	O
known	O
as	O
greenhouse	O
gases	O
–	O
and	O
aerosols	O
.	O
</s>
<s>
Any	O
such	O
alteration	O
is	O
a	O
radiative	B-Algorithm
forcing	I-Algorithm
,	O
which	O
along	O
with	O
its	O
feedbacks	O
,	O
ultimately	O
changes	O
the	O
balance	O
.	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
is	O
defined	O
as	O
:	O
</s>
<s>
"	O
Radiative	B-Algorithm
forcing	I-Algorithm
is	O
a	O
measure	O
of	O
the	O
influence	O
a	O
factor	O
has	O
in	O
altering	O
the	O
balance	O
of	O
incoming	O
and	O
outgoing	O
energy	O
in	O
the	O
Earth-atmosphere	O
system	O
and	O
is	O
an	O
index	O
of	O
the	O
importance	O
of	O
the	O
factor	O
as	O
a	O
potential	O
climate	O
change	O
mechanism	O
.	O
</s>
<s>
In	O
this	O
report	O
radiative	B-Algorithm
forcing	I-Algorithm
values	O
are	O
for	O
changes	O
relative	O
to	O
preindustrial	O
conditions	O
defined	O
at	O
1750	O
and	O
are	O
expressed	O
in	O
Watts	O
 [ sic ] 	O
per	O
square	O
meter	O
(	O
W/m2	O
)	O
.	O
"	O
</s>
<s>
In	O
simple	O
terms	O
,	O
radiative	B-Algorithm
forcing	I-Algorithm
is	O
"	O
the	O
...	O
rate	O
of	O
energy	O
change	O
per	O
unit	O
area	O
of	O
the	O
globe	O
as	O
measured	O
at	O
the	O
top	O
of	O
the	O
atmosphere.	O
"	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
can	O
be	O
evaluated	O
for	O
its	O
dependence	O
on	O
different	O
factors	O
which	O
are	O
external	O
to	O
the	O
climate	O
system	O
.	O
</s>
<s>
Average	O
annual	O
TSI	O
varies	O
between	O
about	O
1360Wm−2	O
and	O
1362Wm−2	O
( ±	O
0.05	O
%	O
)	O
over	O
the	O
course	O
of	O
a	O
typical	O
11-year	O
sunspot	B-Application
activity	O
cycle	O
.	O
</s>
<s>
Sunspot	B-Application
observations	O
have	O
been	O
recorded	O
since	O
about	O
year	O
1600	O
and	O
show	O
evidence	O
of	O
lengthier	O
oscillations	O
(	O
Gleissberg	O
cycle	O
,	O
Devries/Seuss	O
cycle	O
,	O
etc	O
.	O
)	O
</s>
<s>
TSI	O
variations	O
associated	O
with	O
sunspots	B-Application
contribute	O
a	O
small	O
but	O
non-zero	O
net	O
forcing	O
in	O
the	O
context	O
of	O
decadal	O
climate	O
changes	O
.	O
</s>
<s>
Since	O
the	O
late	O
20th	O
century	O
,	O
average	O
TSI	O
has	O
trended	O
slightly	O
lower	O
along	O
with	O
a	O
downward	O
trend	O
in	O
sunspot	B-Application
activity	O
.	O
</s>
<s>
Multiple	O
satellite-based	O
instruments	O
including	O
MODIS	B-Application
,	O
VIIRs	B-Algorithm
,	O
and	O
CERES	O
have	O
continuously	O
monitored	O
Earth	O
's	O
albedo	O
since	O
1998	O
.	O
</s>
<s>
Similar	O
to	O
TSI	O
,	O
the	O
radiative	B-Algorithm
forcing	I-Algorithm
due	O
to	O
a	O
fractional	O
change	O
in	O
planetary	O
albedo	O
( Δα	O
)	O
is	O
:	O
</s>
<s>
The	O
relationship	O
between	O
and	O
radiative	B-Algorithm
forcing	I-Algorithm
is	O
logarithmic	O
at	O
concentrations	O
up	O
to	O
around	O
eight	O
times	O
the	O
current	O
value	O
.	O
</s>
<s>
Thus	O
over	O
long	O
time	O
scales	O
,	O
water	O
vapor	O
behaves	O
as	O
a	O
system	O
feedback	O
that	O
amplifies	O
the	O
radiative	B-Algorithm
forcing	I-Algorithm
driven	O
by	O
the	O
growth	O
of	O
carbon	O
dioxide	O
and	O
other	O
trace	O
gases	O
.	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
can	O
be	O
a	O
useful	O
way	O
to	O
compare	O
the	O
growing	O
warming	O
influence	O
of	O
different	O
anthropogenic	O
greenhouse	O
gases	O
over	O
time	O
.	O
</s>
<s>
The	O
table	O
and	O
figures	O
below	O
(	O
derived	O
by	O
researchers	O
at	O
NOAA	O
from	O
atmospheric	O
radiative	O
transfer	O
models	O
)	O
show	O
changes	O
since	O
year	O
1979	O
in	O
the	O
radiative	B-Algorithm
forcing	I-Algorithm
of	O
the	O
long-lived	O
and	O
well-mixed	O
greenhouse	O
gases	O
that	O
have	O
been	O
increasing	O
in	O
earth	O
's	O
atmosphere	O
since	O
the	O
industrial	O
revolution	O
.	O
</s>
<s>
The	O
five	O
major	O
greenhouse	O
gases	O
account	O
for	O
about	O
96%	O
of	O
the	O
direct	O
radiative	B-Algorithm
forcing	I-Algorithm
by	O
long-lived	O
greenhouse	O
gas	O
increases	O
since	O
1750	O
.	O
</s>
<s>
The	O
table	O
also	O
includes	O
an	O
"	O
Annual	O
Greenhouse	O
Gas	O
Index	O
"	O
(	O
AGGI	O
)	O
,	O
which	O
is	O
defined	O
as	O
the	O
ratio	O
of	O
the	O
total	O
direct	O
radiative	B-Algorithm
forcing	I-Algorithm
due	O
to	O
long-lived	O
greenhouse	O
gases	O
for	O
any	O
year	O
for	O
which	O
adequate	O
global	O
measurements	O
exist	O
to	O
that	O
which	O
was	O
present	O
in	O
1990	O
.	O
</s>
<s>
For	O
2013	O
,	O
the	O
AGGI	O
was	O
1.34	O
(	O
representing	O
an	O
increase	O
in	O
total	O
direct	O
radiative	B-Algorithm
forcing	I-Algorithm
of	O
34%	O
since	O
1990	O
)	O
.	O
</s>
<s>
The	O
decline	O
in	O
CFCs	O
considerably	O
tempered	O
the	O
increase	O
in	O
net	O
radiative	B-Algorithm
forcing	I-Algorithm
.	O
</s>
<s>
An	O
alternative	O
table	O
prepared	O
for	O
use	O
in	O
climate	B-Application
model	I-Application
intercomparisons	O
conducted	O
under	O
the	O
auspices	O
of	O
IPCC	O
and	O
including	O
all	O
forcings	O
,	O
not	O
just	O
those	O
of	O
greenhouse	O
gases	O
.	O
</s>
<s>
Consequently	O
,	O
the	O
planet	O
's	O
'	O
instantaneous	O
radiative	B-Algorithm
forcing	I-Algorithm
 '	O
(	O
IRF	O
)	O
is	O
also	O
dynamic	O
and	O
naturally	O
fluctuates	O
between	O
states	O
of	O
overall	O
warming	O
and	O
cooling	O
.	O
</s>
<s>
The	O
data	O
analysis	O
has	O
also	O
been	O
done	O
in	O
a	O
way	O
that	O
is	O
computationally	O
efficient	O
and	O
independent	O
of	O
most	O
related	O
modelling	B-Application
methods	O
and	O
results	O
.	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
was	O
thus	O
directly	O
observed	O
to	O
have	O
risen	O
by	O
+	O
0.53Wm	O
−2( ±	O
0.11Wm	O
−2	O
)	O
from	O
years	O
2003	O
to	O
2018	O
.	O
</s>
<s>
Radiative	B-Algorithm
forcing	I-Algorithm
can	O
be	O
used	O
to	O
estimate	O
a	O
subsequent	O
change	O
in	O
steady-state	O
(	O
often	O
denoted	O
"	O
equilibrium	O
"	O
)	O
surface	O
temperature	O
( ΔTs	O
)	O
arising	O
from	O
that	O
forcing	O
via	O
the	O
equation	O
:	O
</s>
<s>
where	O
λ	O
is	O
commonly	O
denoted	O
the	O
climate	O
sensitivity	O
parameter	O
,	O
usually	O
with	O
units	O
K/	O
(	O
W/m2	O
)	O
,	O
and	O
ΔF	O
is	O
the	O
radiative	B-Algorithm
forcing	I-Algorithm
in	O
W/m2	O
.	O
</s>
<s>
Historically	O
,	O
radiative	B-Algorithm
forcing	I-Algorithm
displays	O
the	O
best	O
predictive	O
capacity	O
for	O
specific	O
types	O
of	O
forcing	O
such	O
as	O
greenhouse	O
gases	O
.	O
</s>
<s>
It	O
is	O
less	O
effective	O
for	O
other	O
anthropogenic	O
influences	O
like	O
soot	B-Language
.	O
</s>
<s>
A	O
new	O
framework	O
called	O
"	O
effective	O
radiative	B-Algorithm
forcing	I-Algorithm
"	O
or	O
ERF	O
removes	O
the	O
effect	O
of	O
rapid	O
adjustments	O
within	O
the	O
atmosphere	O
that	O
are	O
unrelated	O
to	O
longer	O
term	O
surface	O
temperature	O
responses	O
.	O
</s>
<s>
Other	O
metrics	O
can	O
be	O
constructed	O
for	O
the	O
same	O
purpose	O
as	O
radiative	B-Algorithm
forcing	I-Algorithm
.	O
</s>
<s>
say	O
"	O
...	O
recent	O
experiments	O
indicate	O
that	O
for	O
changes	O
in	O
absorbing	O
aerosols	O
and	O
ozone	O
,	O
the	O
predictive	O
ability	O
of	O
radiative	B-Algorithm
forcing	I-Algorithm
is	O
much	O
worse	O
...	O
we	O
propose	O
an	O
alternative	O
,	O
the	O
'	O
adjusted	O
troposphere	O
and	O
stratosphere	O
forcing	O
 '	O
.	O
</s>
<s>
We	O
present	O
GCM	B-Application
calculations	O
showing	O
that	O
it	O
is	O
a	O
significantly	O
more	O
reliable	O
predictor	O
of	O
this	O
GCM	B-Application
's	O
surface	O
temperature	O
change	O
than	O
radiative	B-Algorithm
forcing	I-Algorithm
.	O
</s>
<s>
It	O
is	O
a	O
candidate	O
to	O
supplement	O
radiative	B-Algorithm
forcing	I-Algorithm
as	O
a	O
metric	O
for	O
comparing	O
different	O
mechanisms	O
...	O
"	O
.	O
</s>
<s>
In	O
this	O
quote	O
,	O
GCM	B-Application
stands	O
for	O
"	O
global	B-Application
circulation	I-Application
model	I-Application
"	O
,	O
and	O
the	O
word	O
"	O
predictive	O
"	O
does	O
not	O
refer	O
to	O
the	O
ability	O
of	O
GCMs	O
to	O
forecast	O
climate	O
change	O
.	O
</s>
<s>
Therefore	O
,	O
the	O
concept	O
of	O
radiative	B-Algorithm
forcing	I-Algorithm
has	O
been	O
evolving	O
from	O
the	O
initial	O
proposal	O
,	O
named	O
nowadays	O
instantaneous	O
radiative	B-Algorithm
forcing	I-Algorithm
(	O
IRF	O
)	O
,	O
to	O
other	O
proposals	O
that	O
aims	O
to	O
relate	O
better	O
the	O
radiative	O
imbalance	O
with	O
global	O
warming	O
(	O
global	O
surface	O
mean	O
temperature	O
)	O
.	O
</s>
<s>
In	O
this	O
sense	O
the	O
adjusted	O
radiative	B-Algorithm
forcing	I-Algorithm
,	O
in	O
its	O
different	O
calculation	O
methodologies	O
,	O
estimates	O
the	O
imbalance	O
once	O
the	O
stratosphere	O
temperatures	O
has	O
been	O
modified	O
to	O
achieve	O
a	O
radiative	O
equilibrium	O
in	O
the	O
stratosphere	O
(	O
in	O
the	O
sense	O
of	O
zero	O
radiative	O
heating	O
rates	O
)	O
.	O
</s>
<s>
This	O
new	O
methodology	O
is	O
not	O
estimating	O
any	O
adjustment	O
or	O
feedback	O
that	O
could	O
be	O
produced	O
on	O
the	O
troposphere	O
(	O
in	O
addition	O
to	O
stratospheric	O
temperature	O
adjustments	O
)	O
,	O
for	O
that	O
goal	O
another	O
definition	O
,	O
named	O
effective	O
radiative	B-Algorithm
forcing	I-Algorithm
has	O
been	O
introduced	O
.	O
</s>
<s>
In	O
general	O
the	O
ERF	O
is	O
the	O
recommendation	O
of	O
the	O
CMIP6	O
radiative	B-Algorithm
forcing	I-Algorithm
analysis	O
although	O
the	O
stratospherically	O
adjusted	O
methodologies	O
are	O
still	O
being	O
applied	O
in	O
those	O
cases	O
where	O
the	O
adjustments	O
and	O
feedbacks	O
on	O
the	O
troposphere	O
are	O
considered	O
not	O
critical	O
,	O
like	O
in	O
the	O
well	O
mixed	O
greenhouse	O
gases	O
and	O
ozone	O
.	O
</s>
