Download Decadal variations

Recent changes in Earth’s
albedo and its implications
for climate change
Enric Pallé
Summary
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The importance of the albedo
Earthshine albedo measurements
Albedo changes 1983-2004
Implications and controversy
The application of the eartshine to
extrasolar planets
Conclusions
The Importance of
the Earth’s albedo
T has increased
over the past
150 years by
~0.6 oC
Increase
rate ‘unseen’
before !!
Trend of global annual surface temperature relative to 1951-1980 mean.
Source: NASA GISS
Important scientific and social
questions
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How is the climate changing?
Why is the climate changing?
 Natural
variability of the system?
 Exogenous factors?
 Human activities?
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How accurately can future changes be
predicted?
What can/should be done about climate
changes?
The albedo sets the input to
the climate heat engine
C
Pin  C R (1  A); Pout  4 R  T ; T 
(1  A);
4
2
E
Solar constant
2
E
Albedo
4
GHG
4
A ~ 0.30
The climate is sensitive to A
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The average energy input from the sun is
C(1-A)/4 = 240 W/m2
Changing A by 0.01 changes this by 3.4 W/m2
This is climatologically significant
All anthropogenic greenhouse gases over last 150 years
result in 2.4 W/m2
 Doubling CO2 results in about twice this amount
 I will shown changes of about 6-7 W/m2 in just 15 years
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Linearization of the power balance (absent feedbacks)
gives
dT / dA ~ -1.5K / 0.01
The earth’s albedo is highly
variable
Clear Overcast
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Local albedo depends upon:
 Surface
type
 Meteorology (clouds)
 Solar zenith angle (time of day)
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The global albedo varies with the
seasons
 North/South
land asymmetry
 Snow/ice cover
 Cloud patterns
Land
0.16
0.50
Ocean
0.08
0.44
Desert
0.23
Snow
0.68
Earthshine albedo
measurements
The Earthshine Project: Photometry goals
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The Moon enables us to monitor one aspect of climate change, the
earth’s reflectance
Observe earthshine to determine absolutely calibrated, large-scale,
high-precision measurements of the earth’s reflectance
Look for secular, seasonal and long-term
variations in the albedo (like over a solar
cycle)
Transient phenomena like El Niño or
volcanic eruptions
Simulate the observational results
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Compare with observations
Calibrate treatment of cloud cover
Earthshine measurements of the Earth’s
large-scale reflectance
Waning / morning
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The Earthshine is the ghostly
glow on the dark side of the
Moon
Origin of Earthshine first
explained by Leonardo da Vinci
First measured by Danjon
beginning in 1927-34 and by
Dubois 1940-60.
ES/MS = albedo (+ geometry
and moon properties)
6” ES telescope at the Big
Bear Solar Observatory
Data Analysis and Issues
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Bright side and dark side images with a ‘blocking’
filter
Scattered light (bright side 104 times brighter)
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Optics, atmosphere
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Defining the spots (lunar libration)
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Extrapolation to zero airmass
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Measuring the lunar reflectivity
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Opposition surge
Scattered light correction
Raw
Corrected
Lunar libration complicates
spot definition
Beer’s law (e-az) variation with
airmass
Time
Airmass z ~ sec 
The earthshine can change
hourly
Coverage during one night
15/10/99
Phase = -116
Evening
In the sunlight &
Visible from the Moon
04/09/99
Phase = +110
Morning
Morning Obs. / Waning Moon
Evening Obs / Waxing Moon
Modeling
hourly
variations
Cloudy Asia
North America
Dark Arabian Sea
Dark Atlantic
June Albedo models
Waning observation
run for June 1994-95
and 1999-2001
It is the clouds that
are changing the
albedo and not the
orbital parameters !!
Albedo changes
1983-2004
Changes in the Earth’s albedo over the last
20 years
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Earthshine Observations: December 1998 – present
ISCCP data June 1983 – September 2001 (to be
updated)
International Satellite Cloud Climatology Project
(ISCCP) provides ~100 daily cloud variables on a
(280 km)2 grid
For each observation, calculate double-projected (E-S
and E-M) area average of these variables
Regress observed A* anomaly against the most
significant of these
This allows us to reconstruct the earth’s albedo as
seen from BBSO since 1983
Decadal variation of the
reflectance
Interannual variation: Smooth decline 1983-2000 & recovery 2000-2003
Palle et al., Science, 2006
The proxy implications
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Confidence in our results based on:
94-95 earthshine data agreement
 Positive/negative phases are similar
 Scrambling the data in mock reconstructions time/space
support the trend
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Variation is large
Albedo change is 7 W/m2 ; GHG up to now is 2.4 W/m2
 Equivalent to 2% increase in solar irradiance, a factor 20
more than typical maxima to minima variations
 Reversibility suggests natural variations.
 GCM do not show such variations
 What is the climatic impact? Recent warming
acceleration?
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Not so surprising…
Although A does not only
depend on mean cloud
amount….
….ISCCP data show
reduction in cloud amount
1983-2001
Source: ISCCP web site
The ES results are not inconsistent with
other observations: Albedo IS changing
Ground level insolation trends.
Liepert, GRL (2002)
Radiation anomalies within ± 20o
of the Equator. Wielicki et al.,
Science (2002)
Earth’s albedo Anomalies
Palle et al., Science (2004)
Albedo measured from CERES
We have used data from:
•ES (albedo)
•ES proxy (albedo)
•CERES (albedo)
•ERBE (albedo tropics)
•GOME (albedo)
•BSRN (sunlight ground)
•MODEL(sunlight ground)
Palle et al, GRL, 2005
Palle et al, GRL, 2005
Palle et al, GRL, 2005
ISCCP Updated data to Dec 2004
A climate shift at the turn of the
millenia?
High CA goes up
Low CA goes down
Both mean higher
albedo AND warming
Palle et al., EOS, 2006
ES Summary
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ES is a viable way to monitor the climate system
on large scales and over long times
By combining ES and ISCCP data, we have a
20-year record of the earth’s SW reflectance that
 Shows
surprising interannual coherence and a
large decadal variability that is likely natural
(why??)
 Is not reproduced by current models
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We have analysed ES data and found a
geographical and seasonal consistency in this
increasing trend.
Multi-data Summary
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For the period 1983-2000:
 Global
albedo has decreased by a quantity
between 2 and 6 W/m2
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For the period 2000-2004:
Earthshine, GOME and ISCCP indicate an
albedo increase.
 CERES data shown a decrease
 Calibration? Interpretation?
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Earthshine applications to
the search for extrasolar planets:
Finding vegetation in outer
space
Observing strategy
Cyclically:
Representation of today’s moon
2004 Feb 14
1 Solar spectrum
2 Earthshine spectrum
3 Background (sky) spectrum
Apparent diameter: 32.5’
Some results from
Mount Palomar 60’’
Echelle Spectrograph
Moonshine: absorption local
atmosphere + solar spec.
Earthshine: absorption local
atmosphere + twice the global
atmosphere + solar spec.
ES/MS: twice the global
atmosphere (not exactly…)
Ha Solar Line
Spectral Albedo of the Earth 2003/11/19
Rayleigh Scattering
Chappuis Ozone band
B-O2
A-O2
Atmospheric
Water vapor
Montañés Rodriguez et al., ApJ, 2005
Comparison Photometry- Spectroscopy
Montañés-Rodriguez et al. , ApJ, 2005
Vegetation spectral
signature
Leaf reflectance and the global Earth’s
leaf structure
0.7
param
param
param
param
0.6
=
=
=
=
1.0
1.5
2.5
3.0
0.5
0.4
0.3
0.2
0.1
0
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0
500
1000
1500
wavelength (nm)
2000
2500
(Jacquemoud, et.al. 1990)
Leaf reflectance causes the known as “red edge” at 700nm
Has been detected from aircraft albedo measurements.
Also from satellites over spatially resolved green areas.
Can it be detected at global scales? 60% of Earth’s surface
is covered by clouds …
Modeling the Earthshine with
simultaneous cloud data
Global cloud data has
recently been released
and allow us a precise
modeling of the
earthshine-contributing
area during our
observations
Montañés-Rodriguez et al., ApJ, 2006 (submitted)
Comparison data-models
Montañés-Rodriguez et al., ApJ, 2006 (submitted)
Tentative detection of
vegetation on Earth
A 2% change in the red edge slope
Vegetation ‘visibility’
as a function of time
Peak in vegetation
contribution during
certain times/lunar
phases:
An ‘effective’
geographical
resolution
Palle et al., ApJ, 2006 (submitted)
Red Edge simulation for ideal conditions
Palle et al., ApJ, 2006 (submitted)
Analogy Earthshine – Extrasolar planet
28 days
PROBLEMS:
-Few photons
-Angular dist
1 year
Palle et al., ApJ, 2006 (submitted)
ES Future
Earthshine Coverage from
BBSO
Time in the earthshine * lunar cosine
Coverage with simultaneous
observations
Four station simulation
Planned Robotic Network
The End