220.127.116.11. Carbon Accounting Methods
Various methods have been used to account for GHG mitigation effectiveness
of LULUCF projects. Some of these methods are based on absolute measurements
at a point in time; others take into account the time dimension of carbon sequestration
and storage. These methods are discussed below.
18.104.22.168.1. Stock change method
The method most commonly used to express carbon storage is based on calculating
the difference in carbon stocks between a project and its baseline at a given
point in time. This method is referred to as the stock change method
[previously the flow summation method (Richards and Stokes, 1994)]; measurements
are usually expressed in tons of carbon per hectare. This method is limited,
however, insofar as it provides only a "snapshot" of the carbon fixed: The values
will vary depending on the often arbitrary decision of when to account for the
project's benefits. Furthermore, this method does not differentiate between
projects that earn credits earlier rather than later. For these reasons, this
method does not provide a useful tool for comparison between projects.
For example, Figure 5-2 illustrates a projection of
carbon stored in two hypothetical tree plantation projects with different growth
rates. The arrows illustrate that stock change measurements carried out at time
t1 would provide different results between the two projects, whereas
the same result would be reached if measurements were carried out at time t2.
If measurements were carried out at time t3-after harvesting-an entirely
different result would be reached for both projects in relation to measurements
Figure 5-2: Projection of carbon stored in
two tree plantation projects with different growth rates. For simplicity,
it is assumed that the baseline is zero and that harvesting leads to
an immediate release of all carbon stored. Arrows illustrate the net
carbon storage of the projects at different points in time, calculated
by the stock change method.