Climate Effects of Woody Biomass Systems
Leif Gustavsson
Linnaeus University
Sweden
Bioenergy Australia 2013
Building the future - Biomass for the Environment, Economy and Society
25 - 26 November, 2013
Crowne Plaza Hunter Valle, Australia
Global primary energy use in 2010
(≈500 Exajoule)
•
•
•
•
•
•
•
•
Oil
Coal
Gas
Total fossil
Bioenergy
Nuclear
Total fuel
Other
32.4%
27.3%
21.4%
81.1%
10.0%
5.7%
96.8%
3.2%
Exa = 1018
Source: International Energy Agency, 2012. Key World Energy Statistics
EJ/yr
Primary energy use in IEA “New Policies” scenario
Source: International Energy Agency, 2011.
World Energy Outlook 2011.
Example: Forest residues substitute fossil fuels
Legend
69° N
69° N
Jämtland and Västernorrland
Legend
Sweden
Europe
66° N
66° N
63° N
63° N
60° N
60° N
57° N
57° N
0
125
250
Kilometers
500
0
375
750
Kilometers
1,500
Forest residues (slash) substitute different fossil fuels
in stationary plants at different locations
• A system analysis from forest
area to local (80km), national
(600km) and international
(1100km) large end-users
• Functional unit is 1 MWh of
delivered wood chips at the
local, national and international
large end-users
• Data on forest residues based
on experience in central Sweden
• Fuel cycle fossil emissions are
considered
Reduced fossil CO2 emission if slash substitutes fossil
fuels in stationary plants at different locations
CO2-balance (tonne C/ha)
12
10
8
Local
6
National
4
International
Primary energy
2
0
-2
Natural
gas
Oil
Coal
Source: Gustavsson L, Eriksson L, Sathre R. 2011. Costs and CO2
benefits of recovering, refining and transporting logging residues for fossil
fuel replacement. Applied Energy 88(1): 192-197.
Example: Forest residues substitute fossil fuels
Bioenergy system
Fossil system
1. Fossil fuels are used for biomass
harvest and logistics
2. Forest residues are used for energy
1. Fossil fuels are used for energy
2. Forest residues are left in forest
and gradually decay
We consider annual GHG emissions including biogenic carbon emissions
Human
activities
Anthropogenic climate change:
Chain of events
•GHG
emissions
•Albedo
change
•Aerosols
•Ozone
Radiative
forcing
Emissions time profile influence
the climate impact
Mean
temperature
change
(IPCC 2007)
Physical,
ecological,
and social
disturbances
Greenhouse gases cause an imbalance between incoming and
outgoing radiation - “radiative forcing” heat is trapped
• Integrated over time, cumulative radiative forcing (CRF) is W-s/m2, i.e.
trapped energy per area – a proxy for temperature increase
• The longer a GHG is in the atmosphere the more energy is trapped and the
more climate change occurs
Longwave radiation
(e.g. heat)
Shortwave radiation
(e.g. light)
Figure not to scale!
Greenhouse gases
Atmospheric decay of unit pulses of GHGs
(CO2 )t  0.217 0.259e
( N 2O)t  e
(CH 4 )t  e
t
114
t
172.9
 0.338e
t
18.51
 0.186e
t
1.186
1
0.9
t
12
0.8
N2O
0.7
0.6
CO2
0.5
0.4
0.3
CH4
0.2
0.1
0
0
25
50
75
Years
(IPCC 1997, 2001, 2007)
100
125
150
Radiative forcing (W/m2) due to GHG concentration
change
FCO2

3.7
CO2


 ln 1 
ln(2)

 CO2 ref
FN 2O  0.12 

FCH 4  0.036 





N 2 O  N 2 Oref 


N 2 Oref  f ( M , N )

CH 4  CH 4 ref  CH 4 ref  f ( M , N )
where CO2ref = 383ppmv, N2Oref = 319ppbv, CH4ref = 1774ppbv
• Assumes relatively minor marginal changes in GHG concentrations
• Spectral overlap between N2O and CH4 is accounted for
• Radiative forcing not related to GHGs (e.g. albedo change) is not considered
(IPCC 1997, 2001, 2007)
Changed cumulative radiative forcing per ton of dry biomass
when slash substitute fossil fuels
Adapted from: Sathre R. and Gustavsson L. 2011. Time-dependent
climate benefits of using forest residues to substitute fossil fuels. Biomass
and Bioenergy 35(7): 2506-2516.
Changed cumulative radiative forcing per ton of dry biomass
when slash substitute fossil fuels
Adapted from: Sathre R. and Gustavsson L. 2011. Time-dependent
climate benefits of using forest residues to substitute fossil fuels. Biomass
and Bioenergy 35(7): 2506-2516.
Changed cumulative radiative forcing when slash substitute
fossil coal – sensitivity analysis of energy input for harvest and
transport
Adapted from: Sathre R. and Gustavsson L. 2011. Time-dependent
climate benefits of using forest residues to substitute fossil fuels. Biomass
and Bioenergy 35(7): 2506-2516.
Comparison of biomass and fossil systems
Woody Biomass System
Woody biomass is
used for heat and
power production,
wood frame in
building
construction
Reference Fossil System
Forest strategy:
harvest biomass
Forest strategy:
carbon storage
Forest land
Forest land
1) Conventional management with 109-year
rotation
2) Fertilized management with 69-year rotation
Fossil coal is used
for heat and power
production,
concrete frame in
building
construction
3) Unmanaged and non-harvested management
with 20 % increase (3a) and with 20 % decrease
(3b)
The same energy and housing service from both of the systems
CRF is calculated based on difference in annual GHG emissions between systems
Forest biomass replace concrete constructions –
An apartment building example
Case-study building:
Wood frame
Built in Växjö, Sweden
Reference building:
Reinforced-concrete frame
Hypothetical building with identical
size and function
4 stories, 16 apartments, 1190 usable m2
CO2 balance of building production and of end-life
•
Fossil CO2 emission from primary energy use for production
and distribution of building materials and for assembly and
demolition of buildings
•
CO2 balance of cement reactions (calcination and
carbonation)
•
Use of biomass by-products from forestry and wood
processing
•
Carbon storage in wood products
•
Carbon stocks and flows in forest
•
End-of-life management
Forest management and growth
•Starting point:
•A mature Norway spruce stand located in northern Sweden
conventionally managed with a 109-year rotation period
•Three forest management alternatives:
1.Clear-cut harvest followed by continuation of conventional
management with 109-year rotation period
2.Clear-cut harvest followed by fertilised management with 69-year
rotation period
3.Stand is left unharvested and unmanaged with carbon stock
stabilizing at
(a) 20% below or (b) 20% above conventional harvest level
(rough assumption)
Decay of biomass left in forest
• We assume decay into CO2 at a negative exponential rate
• Decay constants of:
-0.033 for small-diameter logs
-0.046 for stumps and coarse roots
-0.074 for branches and tops
-0.129 for fine roots
-0.170 for needles
Several uncertainties
(Næsset 1999)
(Melin et al. 2009)
(Palviainen et al. 2004)
(Palviainen et al. 2004)
(Palviainen et al. 2004)
Stand level living tree biomass stock for the different forest
management regimes
350
Conventional
Fertilized
Unmanaged (low)
Unmanaged (high)
Living tree biomass (tC/ha)
300
250
200
150
100
50
0
0
20
40
60
80
100
120
140
Time (Years)
160
180
200
220
Source: Haus, S., Gustavsson, L., Sathre, R. (2013). Climate Mitigation
Comparison of Woody Biomass Systems with the Inclusion of Land-use in
the Reference Fossil System (Journal manuscript).
.
240
Stand level CRF for conventional and fertilized forest
management
0
Conventional management
-2
CRF (W s/m2 per ha)
-4
-6
-8
-10
-12
-14
Fertilized management
-16
-18
-20
-22
0
20
40
60
80
100
120
140
160
180
200
220
240
Based on the difference in GHG between the fossil and the biomass system
with varied forest carbon stock in fossil system
Source: Haus, S., Gustavsson, L., Sathre, R. (2013). Climate Mitigation
Comparison of Woody Biomass Systems with the Inclusion of Land-use in
the Reference Fossil System (Journal manuscript).
Stand level CRF for conventional and fertilized forest management
– The black line with excluded forest land-use in reference system
0
Conventional management
-2
CRF (W s/m2 per ha)
-4
-6
-8
-10
-12
-14
Fertilized management
-16
-18
-20
-22
0
20
40
60
80
100
120
140
160
180
200
220
240
Based on the difference in GHG between the fossil and the biomass system
Source: Haus, S., Gustavsson, L., Sathre, R. (2013). Climate Mitigation
Comparison of Woody Biomass Systems with the Inclusion of Land-use in
the Reference Fossil System (Journal manuscript).
Primary energy use in Sweden 2010
TWh
Oil and oil products
190
Narural gas (18)
Coal and coke
26
Biofuel, peat, etc.
135
Pumped heat (5)
Hydro power
Nuclear power
Wind power (4)
35%
Heat plants
12%
Electricity production*
Other sectors
37%
Pulp and paper industry
13%
Residential, service, etc.
68
166
*in both industry and district heating sectors
Source: Energy in Sweden 2012, Swedish Energy Agency
Annual Swedish bioenergy use
160
140
120
Twh
100
80
60
40
20
0
1980
1985
1990
1995
Year
2000
2005
Source: Swedish Energy Agency: Energy in Sweden 2009, and Kortsiktsprognos 2010
2010
Standing stem volume on Swedish productive
forest land and scenarios for 2010 - 2110
Million m3 stem volume over bark
5000
4000
3000
Environmental scenario
2000
Production scenario
Reference scenario
1000
0
1950
Historic data
1970
1990
2010
2030
Year
2050
2070
2090
2110
Source: Skogsstyrelsen, Skogliga konsekvensanalyser
och virkesbalanser 2008
Conclusions/discussion
• Climate benefits of forest residue use depends strongly on the
fossil energy system that is substituted
• Substituting coal in stationary plants consistently results in
large climate benefits
• Substituting transportation fuels results in initial climate
impacts, followed by modest long-term climate benefits
• Long-distance transport of forest residues has a minor impact
on climate benefits
Conclusions/discussion
• The radiative forcing from forest management emissions
is very low
• The material and energy substitution effects dominate the
climate benefits
• Forest fertilization can significantly increase biomass
production
• Climate benefits from material and energy substitution
significantly increase when forest fertilization is use