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Recent changes in Earths albedo and its implications for climate change

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Title: Recent changes in Earths albedo and its implications for climate change


1
Recent changes in Earths albedo and its
implications for climate change
  • Enric Pallé

2
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

3
The Importance of the Earths albedo
4
  • 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
5
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?

6
The albedo sets the input to the climate heat
engine
7
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

8
The earths albedo is highly variable
  • Local albedo depends upon
  • Surface type
  • Meteorology (clouds)
  • Solar zenith angle (time of day)
  • The global albedo varies with the seasons
  • North/South land asymmetry
  • Snow/ice cover
  • Cloud patterns

9
Earthshine albedo measurements
10
The Earthshine Project Photometry goals
  • The Moon enables us to monitor one aspect of
    climate change, the earths reflectance
  • Observe earthshine to determine absolutely
    calibrated, large-scale, high-precision
    measurements of the earths 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

11
Earthshine measurements of the Earths
large-scale reflectance
Waning / morning
  • 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)

12
6 ES telescope at the Big Bear Solar Observatory
13
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

14
Scattered light correction
15
Lunar libration complicates spot definition
16
Beers law (e-az) variation with airmass
17
The earthshine can change hourly
18
Coverage during one night
15/10/99 Phase -116 Evening
In the sunlight Visible from the Moon
04/09/99 Phase 110 Morning
19
Morning Obs. / Waning Moon
Evening Obs / Waxing Moon
20
Modeling hourly variations
21
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 !!
22
Albedo changes 1983-2004
23
Changes in the Earths albedo over the last 20
years
  • 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 earths albedo
    as seen from BBSO since 1983

24
Decadal variation of the reflectance
Interannual variation Smooth decline 1983-2000
recovery 2000-2003
Palle et al., Science, 2006
25
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?

26
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
27
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)
Earths albedo Anomalies Palle et al., Science
(2004)
28
Albedo measured from CERES
29
  • 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
30
Palle et al, GRL, 2005
31
Palle et al, GRL, 2005
32
ISCCP Updated data to Dec 2004
33
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
34
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 earths SW reflectance that
  • Shows 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.

35
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 decrease
  • Calibration? Interpretation?

36
Earthshine applications to the search for
extrasolar planets Finding vegetation in outer
space
37
Observing strategy
Representation of todays moon
  • Cyclically
  • 1 Solar spectrum
  • 2 Earthshine spectrum
  • 3 Background (sky) spectrum

2004 Feb 14
Apparent diameter 32.5
38
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…)

H? Solar Line
39
Spectral Albedo of the Earth 2003/11/19
Montañés Rodriguez et al., ApJ, 2005
40
Comparison Photometry- Spectroscopy
Montañés-Rodriguez et al. , ApJ, 2005
41
Vegetation spectral signature
42
Leaf reflectance and the global Earths
(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
    Earths surface is covered by clouds …

43
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)
44
Comparison data-models
Montañés-Rodriguez et al., ApJ, 2006 (submitted)
45
Tentative detection of vegetation on Earth
A 2 change in the red edge slope
46
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)
47
Red Edge simulation for ideal conditions
Palle et al., ApJ, 2006 (submitted)
48
Analogy Earthshine Extrasolar planet
28 days
PROBLEMS -Few photons -Angular dist
1 year
Palle et al., ApJ, 2006 (submitted)
49
ES Future
50
Earthshine Coverage from BBSO
Time in the earthshine lunar cosine
51
Coverage with simultaneous observations
Four station simulation
52
Planned Robotic Network
53
The End
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