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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 Pall é. 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.

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Recent changes in Earth’s albedo and its implications for climate change

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  1. Recent changes in Earth’s 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 Earth’s 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. Solar constant Albedo GHG 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 earth’s 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 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

  11. Earthshine measurements of the Earth’s 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. Corrected Raw Scattered light correction

  15. Lunar libration complicates spot definition

  16. Airmass z ~ sec  Time Beer’s 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. Cloudy Asia North America Dark Arabian Sea Dark Atlantic 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 Earth’s 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 earth’s 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) Earth’s 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 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 • 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 tothe search for extrasolar planets: Finding vegetation in outer space

  37. Observing strategy Representation of today’s moon Cyclically: 1 Solar spectrum 2 Earthshine spectrum 3Background (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. Rayleigh Scattering Chappuis Ozone band B-O2 A-O2 Atmospheric Water vapor 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 Earth’s (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 …

  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

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