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The Impact of Albedo Change on Carbon Sequestration Strategies

Maithilee KundaGregg Marland Lorenza Canella

Bernhard SchlamadingerNeil Bird

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What is albedo?

albedo = reflected radiation incident radiation

albedo = 0.5 albedo = 1.0albedo = 0.0

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Land albedo is a function of...

Vegetation Snow cover Soil color Elevation and slope Time of day Time of year Latitude ... ?

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Albedos of Different Land Covers

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Why do we care?

land cover change causes albedo change, which effects the surface energy balance

in particular, field to forest causes a BIG change, especially in snowy conditions

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Global effects of albedo change

Bonan, Pollard, & Thompson. (1992) “Effects of boreal forest vegetation on global climate.” Nature: 359.

– boreal deforestation has a cooling effect– cooling perpetuated by thermal reservoir of

oceans and by ice-albedo positive feedback Betts (2000). “Offset of the potential carbon sink from boreal

forestation by decreases in surface albedo.” Nature: 408.

– albedo warming effect is significant in magnitude compared to cooling effect of carbon sequestration

– warming may offset cooling in boreal regions

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Studying albedo change locally

1 hectare = 10,000 m2

reforestation of fields– deciduous or coniferous

varying latitudes– more snow cover at higher latitudes:

more albedo effect– less incoming radiation at higher latitudes:

less albedo effect

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A simple beginning

Albedo as a function of– land cover– month– snow cover

Simple radiation model using NREL data of average monthly solar insolation– no variable for cloud cover– no hydrologic cycle or latent heat fluxes

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Example: Caribou, Maine

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Example: Caribou, Maine

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The basic logic

A change in local carbon stocks Creates a local change in surface albedo Creates a local change in the mean annual

radiative flux Causes a global mean annual radiative

forcing Which can be equated with a change in

atmospheric carbon burden Which we compare to the initial change in

local carbon stocks

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Albedo change to carbon change

Mean annual radiative forcing F

Atmospheric CO2 equivalence:F = 5.35 ln (1 + C / C)

Terrestrial carbon equivalence T:T = (Mc / Ma) m C

adapted from Betts, 2000

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GORCAM

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The time-scale issue

Change in land surface generates a permanent change in surface albedo

A pulse of CO2 to (or from) atmosphere will decay with time as atmosphere equilibrates with the rest of the global carbon cycle

Therefore, we treat all flows of carbon as annual pulses and let them decay with time.– CO2(t) = CO2(initial) {a0 + ∑aie-t/zi} for i = 1 to 4;

from Maier-Reimer and Hasselman, 1987

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CO2 decay function

CO2 decay function

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 50 100 150

Year

Remainder

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Preliminary results:carbon stock changes - Worcester, MA

Deciduous reforestation

-50

0

50

100

150

200

250

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Year

Net

Seq

ues

trat

ion

[tC

/ha] AGB

Fine root litter

Woody root litter

Foliage litter

Woody litter

Roots

Soil

total

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Preliminary results:carbon stock changes – Caribou, ME

Coniferous reforestation

-20

0

20

40

60

80

100

120

140

160

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

Year

Net

Seq

ues

trat

ion

[tC

/ha] AGB

FR litter

WR litter

Foliage litter

Woody litter

Roots

Soil

total

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Preliminary results:radiative impacts – Worcester, MA

90% Canopy closure

Deciduous reforestation

-35

-30

-25

-20

-15

-10

-5

0

5

10

15

20

0 50 100 150

Year

An

nu

al F

orc

ing

[W

/m2]

Total

Albedo

Sequestration

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Coniferous reforestation

-30

-20

-10

0

10

20

30

40

0 50 100 150

Year

An

nu

al F

orc

ing

[W

/m2]

Total

Albedo

Sequestration

Preliminary results:radiative impacts – Caribou, ME

90% Canopy closure

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Further albedo investigations

better albedo representation– vegetation type, growth rates– snow cover, climate-vegetation feedbacks

GORCAM model– alternate scenarios involving forest

products and bioenergy production ways to think about clouds and latent heat

– might temper albedo effect

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Conclusions

Complex system This study only estimates relative

magnitudes of albedo effect and sequestration effect, which seem to be comparable

Carbon balance is not the whole story Surface energy balances appear to be

important and need systematic consideration

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Acknowledgements

DOE Global Change Education Program (GCEP)

DOE Office of Science, Biological and Environmental Research (BER)