Biomass Carbon Neutrality in the Context
of Forest-based Fuels and Products
Al Lucier, NCASI (alucier@ncasi.org)
Reid Miner, NCASI (rminer@ncasi.org)
May 2010
Annual U.S. Production of Renewable Materials
and Biomass Energy Feedstock Circa 2005
Dry Weight
Production Category
in Millions
of Tons
Products & Feedstock from Forests
249
Corn to Ethanol
18
Other
45
Total
322
2
Forest Sector & Climate Mitigation
“In the long term, a sustainable forest
management strategy aimed at maintaining or
increasing forest carbon stocks, while
producing an annual sustained yield of timber,
fiber or energy from the forest, will generate
the largest sustained mitigation benefit.”
IPCC 4th Assessment Report (2007)
The “neutral”
biomass carbon cycle
VS
Carbon transfers from
geological reserves
CO2
Biomass
Carbon
Biogenic carbon is part of a relatively
rapid natural cycle that impacts
atmospheric CO2 only if the cycle is out
of balance
Fossil Fuel
Biogenic CO2
Atmosphere
Non-biogenic CO2
Atmosphere
Fossil fuel combustion transfers geologic
carbon into the atmosphere. It is a oneway process
4
In Real Landscapes, Carbon Uptake & Release
Vary in Time & Space
Implications for Carbon Accounting
• Fossil Fuels: CO2 emissions at point of combustion
are dominant factors in “carbon footprints.”
• Forest Biomass Fuels: Changes in forest carbon stocks
can be dominant factors in “carbon footprints.”
• This is why there are different carbon accounting
methods for fossil fuels and biomass fuels.
7
Biomass Carbon Neutrality (BCN)
• Practical Contexts:
– National Greenhouse Gas Inventory & Reporting
– Cap & Trade Programs
– EPA Regulation of CO2
8
National GHG Inventory & Reporting
• BCN means that a CO2 emission factor of zero is
used for biomass fuels at point of combustion.
– Emissions associated with the production of biomass
fuels are measured where they occur.
• National GHG Inventory has two main components:
(1) Emissions other than biogenic CO2
(2) Changes in carbon stocks
• Biogenic CO2 emissions are captured in (2).
– To avoid double counting, a CO2 emission factor of
zero is used for biomass fuels at point of combustion.
9
Cap & Trade Programs
• BCN is used in cap & trade programs to:
– encourage use of biomass fuels in place of fossil fuels.
– maintain consistency with National GHG Reporting.
• Some stakeholders have expressed concerns
about unintended consequences of incentives
in cap & trade programs to use biomass and
other energy options.
10
EPA Regulation of CO2
• BCN is being discussed in context of EPA’s plan to
regulate CO2 as a pollutant under the Clean Air
Act. Key topics include:
– Legal basis for distinguishing between fossil and
biomass sources of CO2.
– Concerns about excessive use of biomass.
– Concerns that regulating CO2 from biomass would
encourage switching from biomass fuels to fossil
fuels.
11
Why Would Eliminating BCN Encourage Switching
from Forest-Based Biomass Fuels to Fossil Fuels?
• At point of combustion, CO2 emissions per unit
of energy produced are generally higher for
biomass fuels than for fossil fuels.
– This is due primarily to the higher water content of
biomass fuels.
• CO2 emissions at point of combustion could be
reduced by shifting fuel mix away from biomass.
– However, overall CO2 emissions would increase in
most cases.
12
Biomass Carbon Neutrality
• Does not measure reductions in GHG emissions
attributable to using bioenergy instead of fossil
energy.
13
Quantifying GHG Benefits of Bioenergy
• Construct scenarios.
• Estimate cumulative emissions for
each scenario.
14
What if a new biomass production system is gradually
replacing forest that has higher carbon stocks?
Biomass energy
Fossil fuel energy
Cumulative CO2 combustion emissions
Net Cumulative CO2 combustion emissions
Net cumulative emissions for biomass system increase to reflect stock losses , but
stop increasing after all plots have been converted to production forest.
Time
Time
15
Biomass energy
Fossil fuel energy
Cumulative CO2 combustion emissions
Net Cumulative CO2 combustion emissions
This increases the time required for biomass to
show net benefits, but after the “break even
point” the benefits of biomass continue to accrue.
Time
Biomass
lower from
here forward
Time
16
Biomass energy
Fossil fuel energy
Cumulative CO2 combustion emissions
Net Cumulative CO2 combustion emissions
If reductions in land-based carbon are lower, the
time to “break even” is reduced.
Time
Biomass
lower from
here forward
Time
17
Biomass energy
Fossil fuel energy
Cumulative CO2 combustion emissions
Net Cumulative CO2 combustion emissions
Of course, the opposite can happen. Land can be
converted to higher carbon stocks to provide
biomass energy (e.g. afforestation).
Time
Cumulative fossil fuel
carbon emissions continue
to increase indefinitely
Time
Cumulative net biomass emissions
remain below zero
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Net Cumulative biogenic CO2
emissions
So, we have seen that the net cumulative emissions of
biogenic carbon vary depending on whether and how
the overall carbon stocks on the land are changing.
Convert land to much
lower carbon stocks
In the United States, carbon stocks on
wood-producing land are stable or
increasing, so the national situation is
best represented by this line.
Convert land to somewhat
lower carbon stocks
Keep land in same
general forest type
Time
Afforestation or other
increase in carbon density
This means that the forest biomass
carbon placed in the atmosphere is
offset by new forest growth on woodproducing land
19
Timberland Growth/Removal Ratio By Region
5.00
4.50
Rocky Mtn
4.00
3.50
3.00
2.50
North
2.00
1.50
Pacific
Coast
1.70
1.00
1.37
1.22
South
1.05
0.50
1976
1986
North
South
1996
Rocky Mtn
2006
Pacific Coast
• Growth-removal ratio is calculated based on annual growth on timberland divided by annual removal as of reported years. No specific data for
growth and removal in between reported years.
Source: Forest Resources of the United States, 2007 – Table 36
20
120
100
80
60
Combustion
emissions
Precombustion
emissions
40
20
Data sources: IPCC, USDOE USLCI Database, other public life cycle databases
Bark fuel
Wood pellets
from the U.S.
Residual oil
Natural gas
0
Bituminous coal
Life cycle GHG emissions, kg CO2 eq./GJ LHV
delivered
“Life Cycle” Emissions of Greenhouse Gases
Other than Biogenic CO2
21
Summary
• US Forest Sector
– A world leader in biomass energy production & use.
– Part of the solution to greenhouse gas mitigation.
• Biomass Carbon Neutrality (BCN)
– In theory, an attribute of biomass energy systems
where the biogenic carbon cycle is in balance.
– In practice, an accounting convention in national
greenhouse gas inventories.
22
Summary
• In the United States,
– forest carbon stocks are stable or increasing;
– therefore, GHG emissions per unit of energy are much
lower for forest biomass fuels than for fossil fuels.
• EPA is considering whether to eliminate BCN for
purposes of regulating CO2 as a pollutant under the
Clean Air Act.
– EPA deferred decision on BCN in “tailoring rule”
– Eliminating BCN in this context would encourage
replacement of biomass will fossil fuels, resulting in
substantial increases in GHG emissions.
23