b) Climate Sensitivity
Although
in
recent
years
great
progress
has
been
achieved
in
climate
sciences,
explanations
of
the
observed
global
warming
over
the
last
century,
in
particular
the
anthro
po
genic
contribu
-
tions
to
this
warming
are
still
quite
contradictorily
discussed.
So,
calculations
of
the
equilibri
-
um
climate
sensitivity
(ECS)
as
a
key
parameter
and
measure
for
the
Earth's
tem
perature
in
-
crease
at
doubled
CO
2
concentration
in
the
atmosphere
diverge
by
more
than
a
factor
of
20
starting
at
about
0.4°C
and
ending
at
more
than
8°C.
Also
the
actual
assessment
report
AR5
[1]
of
the
IPCC
still
specifies
this
quantity
with
a
relatively
wide
range
of
1.5°C
to
4.5°C.
At
the
same
time
it
classi
fies
the
human
influence
on
our
climate
as
extremely
likely
to
be
the
domi
-
nant cause of the observed warming since the mid-20th century.
Since
the
ECS
is
one
of
the
most
important
measures
for
climate
predictions,
it
is
necessary
to
understand
and
to
discover
the
large
discrepancies
between
different
accounting
schemes
ap
-
plied for this quantity.
Spectral Calculations
Therefore,
it
seemed
appropriate
to
retrace
the
main
steps
of
the
IPCC's
preferred
accounting
scheme
and
to
com
pare
this
with
own
studies,
which
are
based
on
extensive
spectral
calcula
-
tions
for
the
short
wave
(sw)
absorptivity
a
SW
of
the
solar
intensity
I
S
in
the
atmosphere,
the
long
wave
(lw)
absorp
ti
-
vity
a
LW
of
the
terrestrial
in
-
tensity
I
T
and
the
re-emitted
power
P
A
of
the
atmosphere
by
GH-gases
with
a
fraction
f
A
in
downward
and
1-f
A
in
up
-
ward direction [2-5].
These
calculations
were
performed
with
almost
900,000
lines
of
the
GH-gases
CO
2
,
water
va
-
por,
methane
and
oz
one,
this
for
228
sublayers
of
the
atmosphere
accoun
ting
for
the
total
and
partial
pres
sure
changes
of
the
gas
es
and
the
lapse
rate,
this
for
14
differ
ent
CO
2
concen
-
trations, dif
ferent cloud covers and three climate zones.
Radiative Forcing and Absorptivities
The
transmission
spectra
and
the
spectral
absorptivities
for
the
sw
and
lw
radiation
show
strong
saturation
over
the
path
lengths
and
a
significant
overlap
of
the
CO
2
lines
with
water
vapor.
Both
effects
contribute
to
fast
saturation
of
the
absorptivities
with
increasing
CO
2
concentration, which can well be approximated by logarithmic graphs.
From
these
calculations
we
derive
the
radiative
forcing
D
F
2xCO2
as
important
parameter
for
the
ECS-calculation.
It
specifies
the
reduced
upwelling
lw
radiation
at
the
top
of
the
atmos
phere
(TOA)
at
doubled
CO
2
concentration
in
the
atmosphere.
As
the
absorptivities
and
thus
the
ra
-
diative
forcing
are
ascending
logarithmically
with
increasing
CO
2
concentration,
it
makes
no
difference to calculate a CO
2
doubling from 280 to 560 ppm or from 380 to 760 ppm.
Advanced Two-Layer Climate Model
Instead
considering
the
radiative
forcing
at
doubled
CO
2
concentration
an
even
improved
de
-
scription
and
characterization
of
EASy
to
GHG
changes
can
be
derived
from
the
primary
quan
-
tities
a
SW
,
a
LW
and
f
A
,
which
are
used
as
the
key
parameters
in
our
advanced
two-layer
climate
model
[4,
5]
to
de
termine
the
ECS-value
as
temperature
increase
at
doubled
CO
2
.
This
two-
layer
climate
mo
del
is
especially
appropriate
to
simulate
the
influence
of
increasing
CO
2
concen
trations on glo
bal warming as well as the impact of solar variations on the clima
te.
It
describes
the
atmosphere
and
the
ground
as
two
layers
acting
simultaneously
as
absorbers
and
Planck
radiators,
and
it
includes
additional
heat
transfer
between
these
layers
due
to
con
-
vection
and
evaporation.
The
model
also
considers
sw
and
lw
scattering
processes
at
the
at
-
mosphere
and
at
clouds
as
well
as
all
common
feedback
pro
cesses
like
water
vapor,
lapse
rate
and
albedo
feedback,
but
additionally
takes
into
account
temperature
dependent
sensible
and
latent heat fluxes as well as a temperature induced and solar induced cloud cover feedback.
This
model
is
implemented
on
a
Visual-Pascal-Platform
(PhysCal)
which
runs
under
Win
-
dows
(see
screen
shot).
It
solves
the
energy-
and
radiation-balance
at
the
Earth’s
surface
and
at
TOA
and
from
this
calculates
and
plots
the
Earth’s
surface
temperature
T
E
(red
graph)
and
the
lower
tropospheric
temperature
T
A
(blue
graph)
as
a
function
of
the
CO
2
concentration.
The
difference of T
E
(
760 ppm
) - T
E
(
380 ppm
) gives directly the ECS, in this case 0.7°C (left display).
Feedbacks
Such
simulations
reproduce
the
basic
ECS-value
(without
feedback
processes),
as
specified
by
the
IPCC,
within
a
few
%.
Significant
differences,
however,
are
observed
with
the
different
feedback
effects
included.
While
the
lapse
rate
and
albedo
influence
were
adopted
from
literature,
the
water
vapor
feedback
is
derived
from
the
sw
and
lw
absorptivity
calculations
performed
for
three
climate
zones
with
different
surface
temperatures
and
humidity.
These
calculations
give
a
positive
feedback
of
not
more
than
14
%
[5],
whereas
the
IPCC
emanates
from an amplification of 100% [1], which after all is 7x larger than our result.
Since
our
calculations
indicate
that
with
increasing
CO
2
concentration
the
air
temperature
is
less
rapidly
increasing
than
the
surface
temperature,
the
sensible
heat
flux
at
the
bound
of
both
layers
rises
with
the
concentration.
As
a
consequence
more
thermal
energy
is
transferred
from
the
surface
to
the
atmosphere.
Similarly,
with
increasing
surface
temperature
also
eva
-
poration
and
precipitation
are
increasing
with
the
ground
temperature.
Both
these
effects
con
-
tribute
to
negative
feedback
and
are
additionally
included
in
the
simulations.
While
the
respec
-
tive
contribution
due
to
sensible
heat
rapidly
declines
with
increasing
cloudiness,
evapo
ration
feedback
with
an
attenuation
of
44
%
is
the
primary
stabilizer
of
the
whole
climate
system.
All
the more it is surprising, that the IPCC obviously did not consider this important effect in AR5.
Clouds
A
special
situation
is
found
for
the
influ
ence
of
clouds
on
the
radiation
and
energy
budget.
From
global
cloud
observations
within
the
International
Satellite
Cloud
Cli
matology
Project
(ISCCP)
over
a
period
of
27
years
it
is
de
-
duced
that
the
global
mean
temperature
is
increasing with decreasing cloud cover.
However,
it
is
not
clear,
if
a
lower
cloud
cover
is
the
consequence
of
the
increasing
temperature,
or
if
the
cloud
cover
is
in
-
fluenced
and
at
least
to
some
degree
con
-
trolled
by
some
other
mechanism,
particu
-
larly
solar
activities.
In
the
first
case
a
strong
amplifying
Temperature
Induced
Cloud
Feedback
(TICF)
had
to
be
considered,
this
for
the
climate
sensitivity
ECS
as
well
as
for
a
respective
solar
sensitivity
SS
(surface
temperature
response
to
a
solar
anomaly
of
0.1
%),
whereas
in
the
other
case
TICF
would
not
exist
for
both
sensitivities
and
only
a
Solar
Induced
Cloud
Feedback
(SICF)
had to be included.
Model Simulations for CO
2
- and Solar Influence
A
deliberate
approach
which
mechanism
really
controls
the
cloud
cover,
is
derived
from
model
simulations,
which
additionally
include
the
solar
effect
and
compare
this
with
the
measured
temperature
increase
over
the
last
century.
These
simulations
show
that
the
observed
global
warming
can
best
be
explained,
when
a
temperature
feedback
on
clouds
only
has
a
minor
influence
(less
than
10
%).
Otherwise
the
calculated
warming
would
be
larger
than
observed,
or TICF would have been overestimated.
Results
With
a
solar
anomaly
of
0.26
%
over
the
last
century
and
dominating
SICF
we
deduce
a
CO
2
climate
sensitivity
of
ECS
=
0.7°C
and
a
solar
sensitivity
of
ESS
=
0.17°C
.
The
increase
in
the
Total
Solar
Irradiance
(TSI)
over
100
years
together
with
the
dominating
SICF
then
contributes
to
a
warming
of
0.47°C
(64
%)
and
the
100
ppm
increase
of
CO
2
over
this
period
causes
addi
-
tional 0.27°C (36 %) in good agreement with the measured warming and cloud cover.
Altogether,
we
find
that
the
positive
feedbacks,
originating
from
clouds,
water
vapor
and
albe
-
do
are
even
overcompensated
by
lapse
rate
and
evaporation
feedback.
Particularly
clouds
have
two
stronger
opposing
effects
on
the
energy
balance,
which
can
neutralize
each
other
or
even
have
an
overall
attenuating
impact
on
the
ECS,
dependent
on
the
mechanisms
respon
-
sible for cloud changes.
From
these
studies
we
conclude,
that
all
constraints
can
best
be
ex
plained
by
a
cloud
feedback
mechanism,
which
is
dominated
by
the
solar
influence,
while
ther
mally
induced
contributions
only
should
have
minor
influence.
But
even
for
the
worst
case
assuming
maximum
TICF
and
a
larger global warming over the last century than observed, the ECS would not exceed 1.2°C.
References and Publications
1.
Fifth Assessment Report (AR5): T. F. Stocker, D. Qin, G.-K. Plattner et al., Eds., Climate Change 2013:
The Physical Science Basis, Cambridge University Press, New York, NY, 2014.
2.
H. Harde, Was trägt CO
2
wirklich zur globalen Erwärmung bei? Spektroskopische Untersuchungen und
Modellrechnungen zum Einfluss von H
2
O, CO
2
, CH
4
und O
3
auf unser Klima, Books on Demand,
Norderstedt 2011, ISBN: 9 783842 371576.
3.
H. Harde, Radiation and Heat Transfer in the Atmosphere: A Comprehensive Approach on a Molecular
Basis, International Journal of Atmospheric Sciences (Open Access), vol. 2013,
http://dx.doi.org/10.1155/2013/503727
4.
H. Harde, Advanced two-layer climate model for the assessment of global warming by CO
2
, Open Journal of
Atmospheric and Climate Change, vol. 1, no. 3, pp. 1–50, 2014, ISSN (Print): 2374-3794,
ISSN (Online): 2374-3808
http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.909.4771&rep=rep1&type=pdf
5.
H. Harde, Radiation Transfer Calculations and Assessment of Global Warming by CO
2
, International
Journal of Atmospheric Sciences, Volume 2017, Article ID 9251034, pp. 1-30 (2017),
https://doi.org/10.1155/2017/9251034
6.
H. Harde, Wie schädlich ist CO
2
wirklich für unser Klima? Contribution on EIKE-Blog, 15. Februar 2019
https://www.eike-klima-energie.eu/2019/02/15/wie-schaedlich-ist-co2-wirklich-fuer-unser-klima/
Download as PDF-File, in German
Conferences
1.
H. Harde, How much CO
2
really contributes to global warming? Spectroscopic studies and modelling of the
influence of H
2
O, CO
2
and CH
4
on our climate, Geophysical Research Abstracts, Vol. 13, EGU2011-4505-1,
2011 , EGU General Assembly 2011.
2.
H. Harde, Was trägt CO
2
wirklich zur globalen Erwärmung bei? Talk on Symposium "Energie und Klima -
Ein Blick in die Zukunft", University Erlangen-Nürnberg together with VDI/VDE, November 2012.
Download contributions under: https://opus4.kobv.de/opus4-fau/frontdoor/index/index/docId/3718.
3.
H. Harde, How much CO
2
and also the Sun contribute to global warming, Conference on 'Basic Science of
a Changing Climate', 7.- 8. September 2018, Porto, Portugal.
4.
H. Harde, Was tragen CO
2
und die Sonne zur globalen Erwärmung bei? 12th International EIKE Klima- und
Energiekonferenz, and 13th International Conference on Climate Change (ICCC-13), Munich,
23. a. 24. November, 2018,
Videos:
https://www.youtube.com/watch?v=ldrG4mn_KCs&feature=youtu.be
12. IKEK am 23. und 24.11.18 Hermann Harde – Wieviel tragen CO2 und die Sonne zur globalen
Erwärmung bei?
Physics & Climate