Supporting Information
1. Estimating C emissions from wood energy use
The description in this section pertains to estimates presented in Table 3 in the article.
The volume of wood used for energy (m3) was converted into dry weight (kg) using a factor to
convert m3 to kg (Table S1). 50% of dry weight wood was assumed to be carbon (C) mass.
Table S1 Conversion factors to convert volume of wood (m3) to dry weight (kg) and to C mass
(kg).
Wood volume
dry weight
carbon mass
1 cubic meter
488.55 Kg
50% of dry weight
Example: If 1,000 m3 of wood were used for energy, C emitted from this amount of wood was
estimated as follows: 1000 m3 * 488.55 kg * 0.5 = 240,275 kg or 240.275 tons of C.
2. Estimating C emissions from logging slash left to decay on forest sites
The description in this section pertains to estimates presented in Table 4 in the article.
The volume of logging residue left to decay on forest site (m3) projected from the
USFPM/GFPM timber market model was first converted into dry weight (kg) using conversion
factors from Table S1. Various decay rates (Table S2) were then applied to estimate cumulative
logging residue C stock after accumulation and decay, beginning from year (2010) up through
2060 using the following equation:
𝐿𝑆𝐴𝑡 = 𝐿𝑆𝐴0 ∗ 𝑒 𝑘∗𝑡
S1
Where 𝐿𝑆𝐴𝑡 is logging residue C after decay to the end of time period t. 𝐿𝑆𝐴0 is the
logging residue at the time of harvest, and k is the decay rate (Table S2). The half-life (HL) for
decay is the year t when 𝑒 𝑘∗𝑡 = 0.5 or when 𝑡𝐻𝐿 =
1
ln(2)
𝑘
.
Table S2 Decay rates used in the study in estimating logging residue C accumulated after decay.
Variable
Value
Decay rate (k)
0.99
0.14
0.04 0.02
0.00
Corresponding half-life* (years)
0.7
5
16.5 32
>500
* Average life span after which logging slash left in initial period becomes decayed.
3. Estimating carbon neutrality (CNt) factors
The description in this section pertains to estimates presented in Table 5 in the article.
Carbon neutrality (CNt) factors were estimated using the following steps:
Step 1: Estimate cumulative emissions due to wood energy use (Table 3), and C stocks
(Table 4) for high wood energy (A1B) and low wood energy (A1BHFW) scenarios. This was
done in 10-year steps, starting at 2010 through 2060.
Step 2: Take the difference in cumulative emissions (Table 3) and C stocks (Table 4)
between scenarios at each time step.
Step 3. Use Equation (4) to estimate CNt factors (Table 5) for each time step.
Note: These estimates of CNt factors implicitly assume that CO2 emissions per unit of
energy for both wood and fossil fuel systems are the same (i.e., wood is as efficient as fossil fuel
systems in terms of CO2 emissions per unit of energy).
4. Estimating cumulative radiative forcing neutrality (CRFNt) factors
The description in this section pertains to estimates presented in Table 5 in the article.
Cumulative radiative forcing (CRFNt) factors were estimated using the following steps:
Step 1: Estimate the radiative forcing (index) of initial emissions (2010 emissions) and
the radiative forcing of emissions added subsequently thereafter up through 2060 using CO2
response function provided by IPCC (2007, page 213, footnote a). According to this CO2
response function, the decay of a pulse of CO2 with time t is given by
2
𝑎0 + ∑3𝑖=1 𝑎𝑖 ∗ 𝑒 −𝑡/𝜏𝑖
S2
Where 𝑎0 =0.217, 𝑎1 =0.259, 𝑎2 =0.338, 𝑎3 =0.186, 𝜏1 =172.9 years, 𝜏2 =18.51 years,
and 𝜏3 =1.186 years. Values of t ranges from 0 (2010) to 50 (2060) years for this study.
Step 2: Estimate the radiative forcing (index) of initial C stock (2010 stock) and radiative
forcing of C stocks added subsequently thereafter up through 2060 using CO2 response function
(Equation S2)
Step 3: Obtain cumulative radiative forcing values for emissions (step 1) and C stocks
(step 2) by summing respective yearly radiative forcing values up through a period. This was
done at 10-year step, starting at 2010 through 2060.
Step 4: Take the difference in cumulative radiative forcing of emissions and cumulative
radiative forcing of C stocks between scenarios at each time step.
Step 5. Use Equation (5) to estimate CRFNt factors (Table 5) for each time step.
Note: these estimated CRFNt factors implicitly assume that CO2 emissions per unit of
energy for both wood and fossil fuel systems are the same (i.e., wood is as efficient as fossil fuel
systems in terms of CO2 emissions per unit of energy).
5. Estimates of CNt and CRFNt factors for the alternative assumptions about the relative
efficiency of wood energy systems over fossil fuel systems in terms of CO2 emissions per
unit of energy
The description in this section pertains to estimates presented in Table 7 in the article.
Alternative estimates of CNt and CRFNt factors are provided for two assumed cases where CO2
emissions per unit of energy from wood system is higher than CO2 emissions per unit of energy
from fossil fuel systems. These two cases include: 1) wood energy system replaces natural gas
generated electricity system that emits 40% of CO2 relative to CO2 emissions per unit of wood
energy systems, and 2) wood energy system replaces coal generated electricity system that emits
75% of CO2 relative to CO2 emissions per unit of wood energy systems. These two cases were
assumed based on study by Manomet Center for Conservation Sciences (2010, page 21, Exhibit
3
2-1). The following steps were taken to estimate the relative efficiency of wood energy system
over fossil fuel systems.
Step 1: Determine CO2 emissions per unit of energy (Kg/MWH) for coal, natural gas and
wood energy systems when generating electricity (Table S3). Table S3 was derived from
Manomet Center for Conservation Sciences (2010, Exhibit 2-1)
Table S3 CO2 emissions (kg/MWH) for wood and fossil fuel system when generating electricity.
Electricity generation pathway
CO2 emissions (kg/MWH)
Coal
992.91
Modern woody biomass plant
1335.83
Natural gas
549.30
Step 2. Determine the relative efficiency of wood energy system (Table S4) in term of
CO2 emissions per unit of energy when wood energy system (e.g., modern woody biomass plant)
replaces coal generated electricity or natural gas generated electricity using Table S3.
Table S4 Relative efficiency of wood energy system in terms of CO2 emissions when wood
energy system substitutes either coal or natural gas systems.
Substituted fossil
Relative CO2 emission efficiency of wood energy system
fuel system
(%)
CO2 emission (kg/MWH) from natural gas/CO2 emission (kg/MWH)
Natural gas
Coal
from modern woody biomass plant = 549.30/1335.83*100 = ≈40%
CO2 emission (kg/MWH) from coal/CO2 emission (kg/MWH) from
modern woody biomass plant = 992.91/1335.83*100 = ≈75%
4
Step 3. Re-estimate CNt and CRFNt for the assumed case 1) when wood energy system
replaces natural gas system (wood is 40% efficient compared to natural gas in terms of CO2
emissions), and case 2) when wood energy system replaces coal system (wood is 75% efficient
compared to coal in terms of CO2 emissions) using the following equations:
𝛥 𝐶 𝑆𝑡𝑜𝑐𝑘𝑠
𝑡
𝐶𝑁𝑡 (𝐸𝐹𝐹) = 1 + 𝛥 𝐶𝑢𝑚𝑚𝑢𝑙𝑎𝑡𝑖𝑣𝑒 𝐸𝑡
/𝐸𝐹𝐹
𝐶𝑅𝐹𝑁𝑡 (𝐸𝐹𝐹) = 1 +
S3
𝐶𝑅𝐹 ( ̅̅̅̅̅̅̅̅̅̅̅̅̅̅
∆𝐶 𝑆𝑡𝑜𝑐𝑘𝑠𝑡 )
̅̅̅̅̅̅
𝐶𝑅𝐹 (∆
𝐸𝑡 ) /𝐸𝐹𝐹
S4
Where EFF is the emissions of the fossil fuel power system per unit energy as a fraction of the
emissions of the wood energy power system per unit energy (ie 0.40 or 0.75).
5