Climate Sensitivity to Solar
Irradiance and Climate Models
„
„
SORCE meeting on Decade
Variations in the Sun and the
Climate. Oct 28,2004.
by David Douglass
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Study 1
Solar Sensitivity
See: Paper by Douglass, Clader and Knox at
http://arxiv.org/physics/papers/0411/ 0411002
„
Sensitivity k
∆I = k ∆T
„
Radiative equilibrium
∆I
∆T
=4
I
T
4I
k0 =
= 0.051
T
2
Measurement of sensitivity
Douglass, Clader, Knox
„
„
from MSU temperatures and satellite irradiances
Gain g
k = 0.10 ± 0.02
k
g = = 2.1
k0
„
Response time
3 months
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Feedback
„
Gain >1 means positive feedback
„
Coupling to El Nino [White]?
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Study 2. The Seasons
(Douglass, Blackman and Knox. Physics Lett. A 325 p315 2004)
Solar Insolation vs Month of Year
Fig 2A
Irradiance
~200W/sqm
Insolation (W/sqm)
„
Solstice
600
400
200
0 to 3 0 N
3 0 S to 0
6 0 S to 3 0 S
3 0 N to 6 0 N
0
Temp
~6 C
0
2
4
6
8
10
12
month of year
Fig 2B
Surface Temperature vs Month of Year
Solstic
305
temperature(K)
„
Solstice
Solstice
295
285
275
60S to 30s
30S to 0
0 to 30N
30N to 60N
265
0
2
4
6
8
10
12
month of year
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Study 2
Sensitivity from seasons
∆T
6C
k=
=
= 0.03C / W / sqm
∆I 200 W / sqm
response time ≈ 2 months
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Study 2
Low sensitivity? Explanation?
„
„
DBK paper
k / k0 = p ⋅ gain
p = dynamic factor
Relaxation time 2 months means that
p~1 and not ~0.2 as had been
assumed.
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Study 2
Negative feedback is required
„
Thus
g ~ 0.5
And Negative feedback is required
„
Mechanism? Lindzen Iris?
„
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Topic 3 General Climate Models
(Douglass, Pearson and Singer. GRL July 2004
DOI: 10.1024/2004GL020103)
„
„
Models “ explain “ surface Temp using
using many parameters
Can not explain many other things
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Altitude Dependence
„
.
Douglass, Pearson
and Singer (GRL July
2004)
Observed Trend is
negative while
models gives
positive trends
Global
400
Tropopause
200
Trend-line (mK/dec)
„
Fig 2A
0
-200
-400
-600
1000
800
600
400
200
100
Pressure [Altitude] (hPA)
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Models. What is wrong?
„
„
Models assume response times ~10s
years. Means that dynamic factor p<1
To explain amplitudes they need
gain>1. This requires positive feedback
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Models. What is wrong?
Positive feedback?
„
„
positive feedback (water vapor) is
postulated and put into the models
There is no observational evidence
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Models. What is wrong?
The response time?
„
„
„
„
„
Observed times are short
Dynamic factor p~1
Gain g not >1
Positive feedback not needed
Observations in fact give negative
feedback
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David Douglass presentation
The End
„ Thank You
„
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