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If an equivalence factor ton-year approach is used, carbon storage could be credited according to the time frame over which storage takes place. Such a crediting system would reduce the need for long-term guarantees, hence the risks associated with long time frames. If forests storing this carbon pool suffer any damage, the proportion of carbon credits lost could be easily calculated. This method also allows for comparisons between projects. The main disadvantage of this method is that there is still a great deal of uncertainty in relation to the permanence of CO2 in the atmosphere-consequently the values of the equivalence parameters Te and Ef. Depending on the manner in which ton-year accounting is used, there may also be disadvantages in relation to when crediting occurs, discouraging the implementation of LULUCF GHG mitigation projects (particularly in the case of the equivalence factor yearly crediting and equivalence-delayed crediting approaches). Table 5-9 provides a comparison of the GHG benefits of each method. Whichever method is chosen, it would need to be made compatible with UNFCCC reporting requirements (Chapter 6).
| Table 5-9: Comparison of GHG benefits attributed to a sequestration project at different points in time, according to different carbon accounting methodologies (t C ha-1). | |||||
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| Method |
Year 20
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Year 20 after Harvest
|
Year 60
|
Year 60 after Harvest
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Balance
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|
|
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| Stock change |
140
|
-140
|
140
|
-140
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0
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| Average storage, with the end of each rotation as denominator |
84
|
0
|
0
|
0
|
84
|
|
(84)
|
(84)
|
(84)
|
(84)
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| Equivalence-adjusted average storage, with minimum required project duration of 55 years (Te = 55)a |
83
|
0
|
0
|
0
|
83
|
|
(28)
|
(28)
|
(83)
|
(83)
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| Equivalence-adjusted average storage, with minimum required project duration of 100 years (Te = 100) |
45
|
0
|
0
|
0
|
45
|
|
(15)
|
(15)
|
(45)
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(45)
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| Stock change crediting with tonne-year liability (Te = 55) |
140
|
-112
|
140
|
-57
|
110
|
| Stock change crediting with tonne-year liability (Te = 100) |
140
|
-136
|
140
|
-100
|
44
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| Ton-year yearly crediting (Te = 55; Ef = 0.0182)b |
28
|
28
|
83
|
83
|
83
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| Ton-year yearly crediting (Te = 100; Ef = 0.010)b |
3
|
4
|
38
|
40
|
40
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Notes: Positive values denote GHG benefits (crediting between parentheses),
and negative values mean "reversal" of benefits (removal of credits). Calculations
are based on an example of an afforestation project conducted for three rotations
of 18 years each. It is assumed that at the end of each rotation, the carbon
stock in the forest reaches 140 t C ha-1, and that harvesting reduces
carbon stocks to zero. Forests are not replanted after the third rotation. For
simplicity, it also is assumed that the baseline is zero. Figures in parentheses
refer to GHG benefits accumulated until that point in time, in case the project
was terminated at that time. a Minimum project duration values were chosen based on different proposed equivalence time factors (Te, the length of time CO2 must be stored as carbon in biomass or soil for it to prevent the cumulative radiative forcing effect exerted by a similar amount of CO2 during its residence in the atmosphere). Moura-Costa and Wilson (2000) propose a Te = 55 years, and Fearnside et al. (2000) propose a Te = 100 years (see Chapter 2). b In both cases, Ef (the equivalence factor used to determine the GHG mitigation benefit of a tonne-year of storage) is calculated linearly by 1/Te. |
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