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

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