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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).

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slide1

Climate Effects of Woody Biomass SystemsLeif GustavssonLinnaeus UniversitySwedenBioenergy 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
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
Primary energy use in IEA “New Policies” scenario

EJ/yr

Source: International Energy Agency, 2011.

World Energy Outlook 2011.

forest residues slash substitute different fossil fuels in stationary plants at different locations
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) largeend-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
slide6
Reduced fossil CO2 emission if slash substitutes fossil fuels in stationary plants at different locations

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
Example: Forest residues substitute fossil fuels

Fossil system

Fossil fuels are used for energy

Forest residues are left in forest and gradually decay

Bioenergy system

Fossil fuels are used for biomass harvest and logistics

Forest residues are used for energy

We consider annual GHG emissions including biogenic carbon emissions

slide8

Anthropogenic climate change:

Chain of events

Human activities

  • GHG emissions
  • Albedo change
  • Aerosols
  • Ozone

Radiative forcing

(IPCC 2007)

Mean temperature change

Emissions time profile influence

the climate impact

Physical,

ecological,

and social

disturbances

slide9

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

  • Integrated over time, cumulative radiative forcing (CRF) isW-s/m2, i.e. trappedenergy 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)

Greenhouse gases

Shortwave radiation

(e.g. light)

Figure not to scale!

slide10

Atmospheric decay of unit pulses of GHGs

N2O

CO2

CH4

(IPCC 1997, 2001, 2007)

Years

slide11

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

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)

slide12

Changed cumulative radiative forcingper 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
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.

slide14
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.

slide15

Comparison of biomass and fossil systems

Woody Biomass System

Reference Fossil System

Woody biomass is used for heat and power production, wood frame in building construction

Forest strategy:

carbon storage

Fossil coal is used for heat and power production, concrete frame in building construction

Forest strategy: harvestbiomass

Forest land

Forest land

1) Conventional management with 109-year rotation

2) Fertilized management with 69-year rotation

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
Forest biomass replace concrete constructions – An apartment building example

Case-study building:

Wood frame

Reference building:

Reinforced-concrete frame

4 stories, 16 apartments, 1190 usable m2

Hypothetical building with identical size and function

Built in Växjö, Sweden

slide17

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
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:
  • Clear-cut harvest followed by continuation of conventional management with 109-year rotation period
  • Clear-cut harvest followed by fertilised management with 69-year rotation period
  • Stand is left unharvested and unmanaged with carbon stock stabilizing at

(a) 20% below or (b) 20% above conventional harvest level

(rough assumption)

slide19

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

slide20

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).

.

slide21

Stand level CRF for conventional and fertilized forest management

Conventional management

Fertilized 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).

.

slide22

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

Conventional management

Fertilized management

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).

.

slide23

Primary energy use in Sweden 2010

Source: Energy in Sweden 2012, Swedish Energy Agency

slide24

Annual Swedish bioenergy use

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

slide25

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

Source: Skogsstyrelsen, Skogliga konsekvensanalyser

och virkesbalanser 2008

conclusions discussion
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 discussion1
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