Page 36 - FAO-IPCC Expert meeting on climate change

Greenhouse gas fluxes from agriculture and land systems: a scoping of mitigation options
3.1 Trends in greenhouse gas emissions from agriculture, forestry and other land uses
There are two types of emission associated with crop and livestock production: those that relate to land clearings
to expand production for new markets; and those that relate to production and management practices. Most deforestation and the conversion of natural ecosystems take place as a result of agriculture expansion. Emissions from such activities amount to between 8.4 to 10.3 gigatonnes of CO2 per annum. Gas emissions that relate to agricultural production are dominated by non-CO2 gases, mostly from agricultural soils, enteric fermentation, manure management and rice cultivation. The AR5 uses four data sources for emissions relating to the agriculture, forestry and other
land use sector,25 and trends across these are consistent. Regional trends show a rise in gas emissions in South Asia, Southeast Asia, Latin America and sub-Saharan Africa, with the largest increase from soils and enteric fermentation. In Eastern Europe, Western Europe and North America, there is evidence of stabilization or a slight decline in agricultural emissions. Various opportunities to reduce net GHG emissions from land use present themselves, notably as a result of agriculture and livestock management, sequestration of organic carbon in pastoral systems and agroforestry.
There are several emissions hotspots in the world, typically tied to livestock (including enteric fermentation and manure management emissions), forests (including emissions from fires, deforestation and wood harvesting), and crops (including paddy rice, cropland soil, and croplands over drained histosols). Emissions are elevated around the Congo Basin (deforestation and livestock), in the Rift Valley (livestock) and in South Asia and Southeast Asia (rice paddies). In the southeastern part of South America and on the Indo-Gangetic Plain, there are crop-related emissions. Emissions intrinsic to soils are found in the Midwestern United States, Western Europe, parts of South Asia and part of East
Asia, where fertilizer and manure applications are significant as a consequence of the rapid growth in meat and dairy consumption during the last four decades. While all types of meat consumption are increasing, monogastrics such as pork and poultry show the strongest rise. Unlike ruminants, emissions associated with monogastrics depend primarily on manure management.
There are also significant mitigation hotspots linked to cropping systems that may be geographically localised but nevertheless significant. One such example is the burning of cereal residues in Indo-Gangetic Plains where ca.90
million tonnes of surplus cereal residues are burned on-farm annually.26 On a global scale, total crop residues burned are quite significant with implications not only for GHG emissions but also public health concerns. In India’s Punjab province, according to one study, about 20 million tonnes of rice and wheat residues out of a total of 37 million tonnes are burned in situ annually, leading to a loss of about 8 million tonnes of carbon equivalent to a CO2 load of about
29 million tonnes per year and a loss of about 1×105 tonnes of nitrogen, in addition to the loss of sulphur and the destruction of beneficial microflora in the soil27 with major implications for soil quality and nutrient use efficiency.28
A number of new findings in land use and agriculture are evident. For example, a recent study29 shows a high loss of soil carbon, especially at northern latitudes. The research also indicates that the soil carbon content in some tropical soils may be increasing, although the dataset applied in the model relates to the temperate zone. There is also evidence that the rate of carbon emissions differs depending on the period required to stabilize organic matter levels under the 1oC warming scenario.30
Organic soils, including peatlands, are known to have high CO2 emissions. Approximately 25 million ha of peatland have been drained across the globe, 60 percent in boreal and cool temperate regions, 5 percent in warm temperate regions and 34 percent in the tropics, mostly in Southeast Asia. These soils contribute nearly a billion tonnes of CO2 equivalent emissions (85 percent as CO2). In addition, fire fertilization of these soils creates further emissions.
25 Two data sets are from the United States Environmental Protection Agency, Edgar and the FAO database.
26 This paragraph is based on a communication from Clare Stirling of CIMMYT, one of the external reviewers.
27 Singh and Sidhu. 2014.
28 Jat et al. (2014).
29 Crowther et al. 2016; ibid.
30 If carbon stabilizes immediately, it is in the order of 30−50 petagrams compared with 200 petagrams if the flow takes more than 30 years to stabilize
FAO-IPCC Expert meeting on climate change, land use and food security