Recent changes in Earth’s albedo and its implications for climate change
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Transcript of Recent changes in Earth’s albedo and its implications for climate change
Recent changes in Earth’s albedo and its implications
for climate change
Enric Pallé
Summary
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
Trend of global annual surface temperature relative to 1951-1980 mean. Source: NASA GISS
T has increased over the past 150 years by ~0.6 oC
Increase rate ‘unseen’ before !!
Important scientific and social questions
How is the climate changing? Why is the climate changing?
Natural variability of the system?Exogenous factors?Human activities?
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
30.0~);1(4
;4);1( 4422 AAC
TTRPARCP EoutEin
Solar constant Albedo GHG
The climate is sensitive to A
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
Linearization of the power balance (absent feedbacks) gives dT / dA ~ -1.5K / 0.01
The earth’s albedo is highly variable
Local albedo depends upon:Surface typeMeteorology (clouds)Solar zenith angle (time of day)
Clear Overcast
Land 0.16 0.50
Ocean 0.08 0.44
Desert 0.23
Snow 0.68
The global albedo varies with the seasonsNorth/South land asymmetrySnow/ice coverCloud patterns
Earthshine albedo measurements
The Earthshine Project: Photometry goals
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
Compare with observations Calibrate treatment of cloud cover
Earthshine measurements of the Earth’s large-scale reflectance
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)
Waning / morning
6” ES telescope at the Big Bear Solar Observatory
Data Analysis and Issues
Bright side and dark side images with a ‘blocking’
filter
Scattered light (bright side 104 times brighter) Optics, atmosphere
Defining the spots (lunar libration)
Extrapolation to zero airmass
Measuring the lunar reflectivity Opposition surge
Scattered light correction
Raw Corrected
Lunar libration complicates spot definition
Beer’s law (e-z) variation with airmass
Time Airmass z ~ sec
The earthshine can change hourly
15/10/99Phase = -116
Evening
04/09/99Phase = +110
Morning
Coverage during one night
In the sunlight & Visible from the Moon
Morning Obs. / Waning Moon Evening Obs / Waxing Moon
Modeling hourly
variations
Cloudy Asia
Dark Arabian Sea Dark Atlantic
North America
It is the clouds that are changing the albedo and not the orbital parameters !!
June Albedo models
Waning observation run for June 1994-95 and 1999-2001
Albedo changes 1983-2004
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
Changes in the Earth’s albedo over the last 20 years
Decadal variation of the reflectance
Interannual variation: Smooth decline 1983-2000 & recovery 2000-2003
Palle et al., Science, 2006
The proxy implications
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
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?
Not so surprising…
….ISCCP data show reduction in cloud amount
1983-2001
Although A does not only depend on mean cloud amount….
Source: ISCCP web site
The ES results are not inconsistent with
other observations: Albedo IS changing
Radiation anomalies within ± 20o
of the Equator. Wielicki et al., Science (2002)
Earth’s albedo AnomaliesPalle et al., Science (2004)
Ground level insolation trends. Liepert, GRL (2002)
Albedo measured from CERES
Palle et al, GRL, 2005
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
ISCCP Updated data to Dec 2004
A climate shift at the turn of the millenia?
High CA goes upLow CA goes down
Both mean higher albedo AND warming
Palle et al., EOS, 2006
ES Summary
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 thatShows surprising interannual coherence and a
large decadal variability that is likely natural (why??)
Is not reproduced by current models We have analysed ES data and found a
geographical and seasonal consistency in this increasing trend.
Multi-data Summary
For the period 1983-2000:Global albedo has decreased by a quantity
between 2 and 6 W/m2
For the period 2000-2004: Earthshine, GOME and ISCCP indicate an
albedo increase.CERES data shown a decreaseCalibration? Interpretation?
Earthshine applications tothe search for extrasolar planets:
Finding vegetation in outer space
Observing strategy
Cyclically:
1 Solar spectrum
2 Earthshine spectrum
3 Background (sky) spectrum
Representation of today’s moon
Apparent diameter: 32.5’
2004 Feb 14
Some results from Mount Palomar 60’’ Echelle Spectrograph
H Solar Line
Moonshine: absorption local atmosphere + solar spec.
Earthshine: absorption local atmosphere + twice the global atmosphere + solar spec.
ES/MS: twice the global atmosphere (not exactly…)
Spectral Albedo of the Earth 2003/11/19
Chappuis Ozone band
B-O2 A-O2
Atmospheric
Water vapor
Rayleigh Scattering
Montañés Rodriguez et al., ApJ, 2005
Comparison Photometry- Spectroscopy
Montañés-Rodriguez et al. , ApJ, 2005
Vegetation spectral Vegetation spectral signaturesignature
Leaf reflectance and the global Earth’s Leaf reflectance and the global Earth’s
0 500 1000 1500 2000 25000
0.1
0.2
0.3
0.4
0.5
0.6
0.7
wavelength (nm)
leaf structure
param = 1.0param = 1.5param = 2.5param = 3.0
Leaf reflectance causes the known as “red edge” at 700nmLeaf reflectance causes the known as “red edge” at 700nm Has been detected from aircraft albedo measurements.Has been detected from aircraft albedo measurements. Also from satellites over spatially resolved green areas.Also from satellites over spatially resolved green areas. Can it be detected at global scales? 60% of Earth’s surface Can it be detected at global scales? 60% of Earth’s surface
is covered by clouds …is covered by clouds …
(Jacquemoud, et.al. 1990)
Montañés-Rodriguez et al., ApJ, 2006 (submitted)
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
Tentative detection of vegetation on Earth
A 2% change in the red edge slope
Palle et al., ApJ, 2006 (submitted)
Peak in vegetation contribution during certain times/lunar phases:
An ‘effective’ geographical resolution
Vegetation ‘visibility’ as a function of time
Palle et al., ApJ, 2006 (submitted)
Red Edge simulation for ideal conditions
Palle et al., ApJ, 2006 (submitted)
Analogy Earthshine – Extrasolar planet
28 days
1 year
PROBLEMS:-Few photons-Angular dist
ES Future
Earthshine Coverage from BBSO
Time in the earthshine * lunar cosine
Coverage with simultaneous observations
Four station simulation
Planned Robotic Network
The End