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

Emission trends

For 2005, agriculture accounted for an estimated emission of 5.1 to 6.1 GtCO2-eq (10–12% of total global anthropogenic emissions of GHGs). CH4 contributed 3.3 GtCO2-eq and N2O 2.8 GtCO2-eq. Of global anthropogenic emissions Errata in 2005, agriculture accounted for about 60% of N2O and about 50% of CH4 (medium agreement, medium evidence). Despite large annual exchanges of CO2 between the atmosphere and agricultural lands, the net flux is estimated to be approximately balanced, with net CO2 emissions of only around 0.04 GtCO2/yr (emissions from electricity and fuel use in agriculture are covered in the buildings and transport sector respectively) (low agreement, limited evidence) [8.3].

Trends in GHG emissions in agriculture are responsive to global changes: increases are expected as diets change and population growth increases food demand. Future climate change may eventually release more soil carbon (though the effect is uncertain as climate change may also increase soil carbon inputs through high production). Emerging technologies may permit reductions of emissions per unit of food produced, but absolute emissions are likely to grow (medium agreement, medium evidence).

Without additional policies, agricultural N2O and CH4 emissions are projected to increase by 35–60% and ~60%, respectively, to 2030, thus increasing more rapidly than the 14% increase of non-CO2 GHG observed from 1990 to 2005 (medium agreement, limited evidence) [8.3.2].

Both the magnitude of the emissions and the relative importance of the different sources vary widely among world regions (Figure TS.19). In 2005, the group of five regions consisting mostly of non-Annex I countries were responsible for 74% of total agricultural emissions [8.3].

Figure TS.19

Figure TS.19: Historic and projected N2O and CH4 emissions (MtCO2-eq.) in the agricultural sector of ten world regions, 1990–2020 [Figure 8.2].

Note: EECCA=Countries of Eastern Europe, the Caucasus and Central Asia.