Emissions Scenarios - IPCC

Scenario Driving Forces 143
(a)
(b)
2000 2050 2100 2000 2050 2100
2000 2050 2100 2000 2050 2100
Figure 3-14: Emissions of carbon dioxide from deforestation: (a) global, (b) Asia, (c) Africa, (d) Latin America. Scenarios
numbers are given m Table 3-7.
deforestation range from zero to 30% of their base-year
estimates.
As emissions from deforestation are more significant in
developing regions than industrial regions, few scenarios of
COj from deforestation are available for industrial regions, so
the focus here is on developing regions only. For Asia,
emissions in all but one scenario (EPA-SCW, 7-1 in Table 3-7)
steadily decline after the base year, and reach 25% or less of
their 1990 value in 2100 (Figuie 3-14b). For Africa, emissions
first increase before eventually decreasing in 2100 to a small
fraction of their 1990 value (Figure 3-14c). In this scenario,
deforestation rates decline in Asia and Africa because of the
depletion of their forests. For Latin America, the wide range of
scenarios reflects the wide range of views about its future rates
of deforestation (Figure 3-14d).
One of the main factors that affects estimates of COj from
deforestation is the assumed deforestation rate, which is
estimated by a wide variety of methods. For example, the
IS92a-IS92f scenarios assume that deforested area is
proportional to population, with a time lag of 25 years, and that
deforestation continues until 25 years after the population
stabilizes or until forests ai-e exhausted (Leggett et al., 1992).
The IMAGE 2.1 emission estimates are based on computed
changes in global land cover, which take into account changing
demand for agricultural commodities. Trexler and Haugen
(1995) compute the rate of tropical deforestation on a countryby-country
basis, and include information from questionnaires.
Jepma (1995) uses a combination of three models (a socioeconomic
model, a wood demand-supply model, and a landuse
model), while Palo et al. (1997) correlate deforestation
rates with income levels. To further confound this situation, the
factors that affect deforestation vary greatly from place to
place, and therefore need to be defined as locally as possible.
Figure 3-15 presents population assumptions of various
deforestation scenarios, together with the assumed or implied
deforestation rates on a per capita basis. The shape of the
emission curves (Fig. 3-14) follows the shape of the
deforestation rate curves, rather than that of the population
assumptions. However, the range of emissions is much larger