REPORTS - SPECIAL REPORTS

Emissions Scenarios


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3.5. Agriculture and Land-Use Emissions

3.5.1. Introduction

The most important categories of land-use emissions are CO2 from net deforestation, CH4 from rice cultivation, CH4 from enteric fermentation of cattle, and N2O from fertilizer application. These sources account for nearly all the land-use emissions of CO2 (Schimel et al., 1995), about 53% of the land-use emissions of CH4 (Prather, et al., 1995), and about 80% of land-use emissions of N2O (Prather, et al., 1995). These estimates, however, have a high uncertainty. Measurements and analyses of other sources of CH4 and N2O (notably biomass burning, landfills, animal waste, and sewage) are relatively rare, but increasing (Bogner et al., 1997, in the literature. Of the scenarios reviewed for this report (see Table 3.7), about 20 address emissions from agriculture and land-use change (Lashof and Tirpak, 1990; Houghton, 1991; Leggett et al., 1992; Matsuoka and Morita, 1994; Alcamo et al., 1998; Alcamo and Kreileman, 1996; Leemans et al., 1996).

Current assessments of GHG emissions indicate that land use or land cover activities make an important contribution to the concentration of GHGs in the atmosphere3; these are referred to as "land-use emissions" in this report4. Of the three most important GHGs, the contribution of land-use emissions to total global CO2 is relatively small (23%), but it is very large for CH4 (74%) and N2O. Furthermore, although land-use emissions make up only a small percentage of global CO2 emissions, they comprise a large part (45%) of CO2 emissions from developing countries, and an even larger percentage of their total CH4 (78%) and N2O (76%) emissions (Pepper et al.,1992). Hence, from a variety of perspectives, the contribution of land-use emissions to total emissions of GHGs is important, and consequently their future trends are relevant to the estimation of climate change and its mitigation.


Table 3-7: Overview of scenarios presented in Section 3.5.

Scenario
Number
Scenario Identification Type(*) Reference

1-1 IS92a IPCC 1992 G R Leggett et al. (1992)
1-2 IS92b IPCC 1992 G R Leggett et al. (1992)
1-3 IS92c IPCC 1992 G R Leggett et al. (1992)
1-4 IS92d IPCC 1992 G R Leggett et al. (1992)
1-5 IS92e IPCC 1992 G R Leggett et al. (1992)
1-6 IS92f IPCC 1992 G R Leggett et al. (1992)
1-7 IS92 S1 : IPCC 1992 Sensitivity 1
(High Deforestation, High Biomass)
G R Leggett et al. (1992)
1-8 IS92 S4 : IPCC 1992 Sensitivity 4
(Halt Deforestation, High Plantation)
G R Leggett et al. (1992)
2-1 Baseline A IMAGE 2.1 G R Alcamo, et al. (1996)
2-2 Baseline B IMAGE 2.1 G R Alcamo, et al. (1996)
2-3 Baseline C IMAGE 2.1 G R Alcamo, et al. (1996)
2-4 Less B1 Changed Trade G R Leemans, et al. (1996)
2-5 Less B1 No Biofuels G R Alcamo and Kreileman (1996)
2-6 Stab 350 All G R Alcamo and Kreileman (1996)
3-1 AIM, Asian Pacific Integrated Model
Land use emission scenario
G R Matsuoka and Morita (1994)
7-1 EPA-SCW EPA (Slowly Changing World) G R Lashof and Tirpak (1990)
7-2 EPA-RCW EPA (Rapidly Changing World) G R Lashof and Tirpak (1990)
7-3 EPA-High Reforestation EPA
(Halt Deforestation, High Reforestation)
G R Lashof and Tirpak (1990)
8-1 H1 Houghton-Population G Houghton (1991)
8-2 H2 Houghton-Exponential Extrapolation G Houghton (1991)

* G = global, R = regional.



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