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