3.5.4.3. What Net Changes in Carbon Stocks from ARD Can Be Expected in the
Future?
To estimate global potential carbon stock changes induced by ARD activities
during the commitment period, Yamagata and Alexandrov (1999) used the land-use
change scenarios obtained from the IMAGE 2.1 model (Alcamo et al., 1998).
The model gives a total carbon stock at maturity of 216 t C ha-1, 142 t C ha-1,
and 90 t C ha-1 for the low-, mid-, and high-latitude regions respectively (Yamagata
and Alexandrov, 1999). These estimates are similar to those made by Dixon et
al. (1994) for low- and mid-latitude (tropical and temperate forests) but
very small compared to the high-latitude (boreal forests) carbon estimates of
Dixon et al. (1994). The Yamagata and Alexandrov (1999) simulations lack the
large soil carbon pools that have accumulated at high latitudes during the past
8,000 to 10,000 years. The simulations yield an emission rate of 1.8 Gt C yr-1
during the commitment period if the scenario of land-use changes suggested by
Leemans et al. (1998) took place.
These estimates for global ARD fluxes would be significantly reduced, however,
if the actual tree canopy cover (<<100 percent) of the ARD lands in each region
is used. In general, higher thresholds (e.g., 40 percent) capture not only clearing
but also forest degradation as a deforestation activity. Higher thresholds also
credit more afforestation and reforestation activities on land already covered
by trees. On the other hand, higher thresholds are not sensitive to conversions
of open forests, giving no credit for establishing open forests and no debit
for clearing them.
To illustrate how thresholds change the ARD potential, we simulated the global
carbon fluxes from ARD activities during the first commitment period. We combined
remotely sensed canopy cover data (Nemani and Running, 1997) with the carbon
stock change model of Yamagata and Alexandrov (1999) and the land-use change
model of Leemans et al. (1998). Each value is predicted assuming the Land Use
definitional scenario, with a different canopy cover threshold (Table
3-18).
|
Table 3-18: Total estimates of carbon fluxes
for Annex I countries during the first commitment period that would be induced
by land-use change based ARD activities since 1990, in Gt C yr-1. Estimates for
non-Annex I countries are given in parentheses to illustrate the carbon potentials
for projects between Annex I and non-Annex I countries. Removals are shown as
positive and emissions as negative numbers.
|
|
| |
Tree Cover Threshold
in Forest Definition
|
All Forests
|
| |
10% Canopy
Cover
|
40% Canopy
Cover
|
Regardless
of Canopy Cover
|
|
| Removals |
0.078
|
0.170
|
0.228
|
| (Gt C yr-1) |
(0.041)
|
(0.174)
|
(0.206)
|
| Emission |
-0.017
|
-0.012
|
-0.017
|
| (Gt C yr-1) |
(-0.586)
|
(-0.478)
|
(-0.591)
|
| Net flux |
0.061
|
0.158
|
0.211
|
| (Gt C yr-1) |
(-0.545)
|
(-0.304)
|
(-0.385)
|
|
The result demonstrates several implications for the Annex I countries. First,
global carbon removals from ARD activities are as high as 0.2 Gt C yr-1. Second,
a lower canopy cover threshold significantly reduces potential carbon removals
from afforestation and reforestation activities and increases potential emissions
from deforestation activities. Third, net carbon removals from ARD activities
decline from 0.16 (40 percent cover threshold) to 0.06 Gt C yr-1 (10 percent
cover threshold).
|