Transcript The Impact of Albedo Change on Carbon Sequestration Strategies

The Impact of Albedo Change on
Carbon Sequestration Strategies
Maithilee Kunda
Gregg Marland
Lorenza Canella
Bernhard Schlamadinger
Neil Bird
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What is albedo?
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albedo = reflected radiation
incident radiation
albedo = 0.0
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albedo = 0.5
albedo = 1.0
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Land albedo is a function of...
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Vegetation
Snow cover
Soil color
Elevation and slope
Time of day
Time of year
Latitude
... ?
Albedos of Different Land Covers
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Why do we care?
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land cover change causes albedo change,
which effects the surface energy balance
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in particular, field to forest causes a BIG
change, especially in snowy conditions
Global effects of albedo change
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Bonan, Pollard, & Thompson. (1992) “Effects of boreal forest
vegetation on global climate.” Nature: 359.
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Betts (2000). “Offset of the potential carbon sink from boreal
forestation by decreases in surface albedo.” Nature: 408.
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boreal deforestation has a cooling effect
cooling perpetuated by thermal reservoir of
oceans and by ice-albedo positive feedback
albedo warming effect is significant in
magnitude compared to cooling effect of
carbon sequestration
warming may offset cooling in boreal
regions
Studying albedo change locally
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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
A simple beginning
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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
Example: Caribou, Maine
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Example: Caribou, Maine
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The basic logic
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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
Albedo change to carbon change
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Mean annual radiative forcing F
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Atmospheric CO2 equivalence:
F = 5.35 ln (1 + C / C)
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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
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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.
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CO2(t) = CO2(initial) {a0 + ∑aie-t/zi} for i = 1 to 4;
from Maier-Reimer and Hasselman, 1987
CO2 decay function
CO2 decay function
1.0
0.9
0.8
0.7
0.6
Remainder
0.5
0.4
0.3
0.2
0.1
0.0
0
50
100
Year
16
150
Preliminary results:
carbon stock changes - Worcester, MA
Deciduous reforestation
250
Net Sequestration [tC/ha]
200
AGB
Fine root litter
Woody root litter
Foliage litter
Woody litter
Roots
Soil
total
150
100
50
0
0
10
20
30
40
50
60
70
80
-50
Year
17
90
100
110
120
130
140
150
Preliminary results:
carbon stock changes – Caribou, ME
Coniferous reforestation
160
140
Net Sequestration [tC/ha]
120
AGB
FR litter
WR litter
Foliage litter
Woody litter
Roots
Soil
total
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
-20
Year
18
90
100
110
120
130
140
150
Preliminary results:
radiative impacts – Worcester, MA
Deciduous reforestation
20
15
Annual Forcing [W/m2]
10
5
90% Canopy closure
0
0
50
100
-5
-10
-15
-20
-25
-30
-35
Year
19
150
Total
Albedo
Sequestration
Preliminary results:
radiative impacts – Caribou, ME
Coniferous reforestation
40
Annual Forcing [W/m2]
30
90% Canopy closure
20
10
Total
Albedo
Sequestration
0
0
50
100
-10
-20
-30
Year
20
150
Further albedo investigations
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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
Conclusions
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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
Acknowledgements
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DOE Global Change Education Program
(GCEP)
DOE Office of Science, Biological and
Environmental Research (BER)