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.

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