IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group III: Mitigation of Climate Change

8.3 Emission trends (global and regional)

With an estimated global emission of non-CO2 GHGs from agriculture of between 5120 MtCO2-eq/yr (Denman et al., 2007) and
6116 MtCO2-eq/yr (US-EPA, 2006a) in 2005, agriculture accounts for 10-12 % of total global anthropogenic emissions of GHGs.
Agriculture contributes about 47% and 58% of total anthropogenic emissions of CH4 and N2O, respectively, with a wide range of uncertainty in the estimates of both the agricultural contribution and the anthropogenic total. N2O emissions from soils and CH4 from enteric fermentation constitute the largest sources, 38% and 32% of total non-CO2 emissions from agriculture in 2005, respectively (US-EPA, 2006a). Biomass burning (12%), rice production (11%), and manure management (7%) account for the rest. CO2 emissions from agricultural soils are not normally estimated separately, but are included in the land use, land use change and forestry sector (e.g., in national GHG inventories). So there are few comparable estimates of emissions of this gas in agriculture. Agricultural lands generate very large CO2 fluxes both to and from the atmosphere (IPCC, 2001a), but the net flux is small. US-EPA, 2006b) estimated a net CO2 emission of 40 MtCO2-eq from agricultural soils in 2000, less than 1% of global anthropogenic CO2 emissions.

Both the magnitude of the emissions and the relative importance of the different sources vary widely among world regions (Figure 8.2). In 2005, the group of five regions mostly consisting of non-Annex I countries was responsible for 74% of total agricultural emissions.

In seven of the ten regions, N2O from soils was the main source of GHGs in the agricultural sector in 2005, mainly associated with N fertilizers and manure applied to soils. In the other three regions - Latin America and The Caribbean, the countries of Eastern Europe, the Caucasus and Central Asia, and OECD Pacific - CH4 from enteric fermentation was the dominant source (US-EPA, 2006a). This is due to the large livestock population in these three regions which, in 2004, had a combined stock of cattle and sheep equivalent to 36% and 24% of world totals, respectively (FAO, 2003).

Emissions from rice production and burning of biomass were heavily concentrated in the group of developing countries, with 97% and 92% of world totals, respectively. While CH4 emissions from rice occurred mostly in South and East Asia, where it is a dominant food source (82% of total emissions), those from biomass burning originated in Sub-Saharan Africa and Latin America and the Caribbean (74% of total). Manure management was the only source for which emissions where higher in the group of developed regions (52%) than in developing regions (48%; US-EPA, 2006a).

The balance between the large fluxes of CO2 emissions and removals in agricultural land is uncertain. A study by US-EPA (2006b) showed that some countries and regions have net emissions, while others have net removals of CO2. Except for the countries of Eastern Europe, the Caucasus and Central Asia, which had an annual emission of 26 MtCO2/yr in 2000, all other countries showed very low emissions or removals.