Climate Effects of Woody Biomass Systems

Leif GustavssonLinnaeus 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 32.4%

• Coal 27.3%

• Gas 21.4%

• Total fossil 81.1%

• Bioenergy 10.0%

• Nuclear 5.7%

• Total fuel 96.8%

• Other 3.2%

Exa = 1018

Source: International Energy Agency, 2012. Key World Energy Statistics

Primary energy use in IEA “New Policies” scenario

Source: International Energy Agency, 2011. World Energy Outlook 2011.

EJ/

yr

Legend

Sweden

Europe

0 750 1,500375

Kilometers

69° N69° N

66° N66° N

63° N63° N

60° N60° N

57° N57° N

Legend

Jämtland and Västernorrland

0 250 500125

Kilometers

Example: Forest residues substitute fossil fuels

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

-2

0

2

4

6

8

10

12

Naturalgas

Oil Coal

CO

2-b

alan

ce (

ton

ne

C/h

a)

Local

National

International

Primary energy

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

Fossil system1. Fossil fuels are used for energy

2. Forest residues are left in forest and gradually decay

Bioenergy system1. Fossil fuels are used for biomass harvest and logistics

2. Forest residues are used for energy

We consider annual GHG emissions including biogenic carbon emissions

Physical,ecological,and social

disturbances

Anthropogenic climate change:Chain of events

Mean temperature

change

Radiative forcing

•GHG emissions

•Albedo change

•Aerosols•Ozone

Human activities

(IPCC 2007)

Emissions time profile influence the climate impact

Greenhouse gasesLongwave radiation

(e.g. heat)

Shortwave radiation(e.g. light)

• 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

Greenhouse gases cause an imbalance between incoming and outgoing radiation - “radiative forcing” heat is trapped

Figure not to scale!

Atmospheric decay of unit pulses of GHGs

186.151.189.1722 186.0338.0259.0217.0)(

ttt

t eeeCO

1142 )(

t

t eON

124 )(

t

t eCH

N2O

CO2

CH4

Years

(IPCC 1997, 2001, 2007)

Radiative forcing (W/m2) due to GHG concentration change

ref

CO CO

COF

2

21ln)2ln(

7.32

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)

),(12.0 2222NMfONONONF refrefON

),(036.0 4444NMfCHCHCHF refrefCH

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

The same energy and housing service from both of the systemsCRF is calculated based on difference in annual GHG emissions between systems

Forest strategy: harvest biomass

Woody Biomass System Reference Fossil System

Forest land

Forest strategy:carbon storage

Forest land

3) Unmanaged and non-harvested management with 20 % increase (3a) and with 20 % decrease (3b)

Fossil coal is used for heat and power

production, concrete frame in

building construction

Woody biomass is used for heat and power production,

wood frame in building

construction

1) Conventional management with 109-year rotation2) Fertilized management with 69-year rotation

Forest biomass replace concrete constructions – An apartment building example

4 stories, 16 apartments, 1190 usable m2

Built in Växjö, Sweden

Case-study building:Wood frame

Reference building:Reinforced-concrete frame

Hypothetical building with identical size and function

• 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

CO2 balance of building production and of end-life

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 (Næsset 1999)

-0.046 for stumps and coarse roots (Melin et al. 2009)

-0.074 for branches and tops (Palviainen et al. 2004)

-0.129 for fine roots (Palviainen et al. 2004)

-0.170 for needles (Palviainen et al. 2004)

Several uncertainties

0

50

100

150

200

250

300

350

0 20 40 60 80 100 120 140 160 180 200 220 240

Livi

ng tr

ee b

iom

ass

(tC/

ha)

Time (Years)

ConventionalFertilizedUnmanaged (low)Unmanaged (high)

Stand level living tree biomass stock for the different forest management regimes

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

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)..

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

0 20 40 60 80 100 120 140 160 180 200 220 240

CRF

(W s

/m2

per h

a)

Conventional management

Fertilized management

Stand level CRF for conventional and fertilized forest management – The black line with excluded forest land-use in reference system

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)..

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

0 20 40 60 80 100 120 140 160 180 200 220 240

CRF

(W s

/m2

per h

a)

Conventional management

Fertilized management

Primary energy use in Sweden 2010

166

68

135

26

190Oil and oil products

Narural gas (18)Coal and coke

Biofuel, peat, etc.

Hydro power

Nuclear power

Wind power (4)

Pumped heat (5)

Heat plants

Electricity production*

Other sectors

Pulp and paper industry

Residential, service, etc.

35%

12%

37%

13%

TWh

*in both industry and district heating sectors

Source: Energy in Sweden 2012, Swedish Energy Agency

Annual Swedish bioenergy use

Source: Swedish Energy Agency: Energy in Sweden 2009, and Kortsiktsprognos 2010

Standing stem volume on Swedish productive forest land and scenarios for 2010 - 2110

0

1000

2000

3000

4000

5000

1950 1970 1990 2010 2030 2050 2070 2090 2110Year

Mill

ion

m3

ste

m v

olu

me

ove

r b

ark

Environmental scenario

Production scenario

Reference scenario

Historic data

Source: Skogsstyrelsen, Skogliga konsekvensanalyser och virkesbalanser 2008

• 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

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