Big Facts on Climate Change, Agriculture and Food Security

• Agricultural practices that reduce greenhouse gas emissions and increase carbon storage could reduce carbon emissions by 1,500–1,600 million tonnes of CO₂ equivalents per year at a carbon price of USD 20 per tonne of CO₂ equivalent (Smith et al. 2008). Improved crop management will be key to mitigating emissions in the agricultural sector. This includes the optimization of nutrient use, the incorporation of nitrogen-fixing legumes in crop rotations and a number of other climate-smart practices.
• About 70% of the mitigation potential is in low- and middle-income countries (Smith et al. 2007).
• The greatest potential source of climate change mitigation in agriculture is carbon sequestered in the soils of cropland, grazing land and rangeland. These soils can store 1,500-4,500 million tonnes of CO₂ equivalents per year (Smith et al. 2007).
• Measuring carbon sequestration is problematic because of high natural variability in soil carbon, difficulties in establishing reliable baselines, problems detecting changes over short time periods or across small spatial extents and a lack of consistency in units and measurement techniques. However, much progress is currently being made in establishing global norms for measurement (Smith et al. 2012).
• Supply-side changes in agricultural and forestry practices, such as changes in land management, could reduce emissions by 1,500 4,300 million tonnes of CO₂ equivalents at carbon prices of between USD 20 and USD 100 per tonne of CO₂ equivalent (Smith et al. 2013).
• Increasing the yield of edible output per unit of emissions generated would contribute to mitigation of agriculture’s contribution to climate change (Garnett et al. 2013).
• However, changes in patterns of consumption in terms of the amounts and the types of foods eaten and discarded (link to supply chain) have a greater potential to reduce emissions than do changes in production (Vermeulen et al. 2012).
• The price of carbon determines the global economic potential for agricultural mitigation—the higher the price, the higher the potential (Smith et al. 2008):
• Up to USD 20 per tonne of CO₂ equivalent: 1500-1600 million tonnes of CO₂ equivalents per year (~3.0% of total global emissions)
• Up to USD 50 per tonne of CO₂ equivalent: 2500–2700 million tonnes of CO₂ equivalents per year (~4.5% of total global emissions)
• Up to USD 100 per tonne of CO₂ equivalent: 4000–4300 million tonnes of CO₂ equivalents per year (~7.5% of total global emissions)
• At low carbon prices, the main mitigation strategies will be based on modification of existing production practices (e.g. changes in tillage, fertilizer application, feed formulation and manure management), while higher prices would stimulate more radical changes in land use, such as forestation and biofuels, allow the use of costly animal-feed-based mitigation options (Smith et al. 2008).
• Tools for comprehensively quantifying greenhouse gas emissions and removals on smallholder farms have multiple uses. Not only can they more accurately measure mitigation benefits from the adoption of sustainable agriculture and land management practices; they also help to compare combinations of practices and evaluate which mitigation options are likely to benefit or undermine farmers’ livelihoods and food security (Seebauer, 2014).
• The mitigation potential in the livestock sector may account for as much as 50% of the total mitigation potential in the agriculture, forestry and land-use sector. (Herrero et al. 2016). This potential can be realised by sustainably intensifying livestock production, promoting carbon sequestration in rangelands, reducing emissions from manures, and through reducing demand for livestock products (Herrero et al. 2016).
• Moderate mitigation policies targeting livestock production systems and land use change associated to livestock could reduce emissions by as much as 2 million tonnes CO2 equivalents per year at a carbon price of USD 10 per tonne of CO2 equivalent, with land-use change accounting for most of this reduction (Havlík et al. 2014).
• Globally, shifts to mixed crop-livestock production systems offer potential to reduce up to 76 million hectares of deforestation (Weindl et al. 2015).
• In low and middle income countries, improved animal feed can achieve a mitigation potential of 0.68 GtCO2eq per year in reduced enteric methane emissions by ruminants , while also improving animal health and productivity (Herrero et al. (2016).
• Reduced global consumption of animal products would reduce emissions. Global adoption of healthy eating guidelines would reduce emissions by 4.3 GtCO2eq per year and universal vegan diets would achieve reductions of 7.8 GtCO2eq per year (Stehfest et al. 2009).
• Reduction of livestock consumption may be an acceptable form of mitigation in high-income countries where consumption is above recommended levels. However, in low and middle income countries, animal sourced food offers valuable protein and micronutrients helping address malnutrition and support families during periods of food insecurity (Rivera-Ferre et al. 2016).

Mitigation options

Cropland management	Mitigation practices include: (i) agronomy; (ii) nutrient management; (iii) tillage/residue management; (iv) water management; (v) rice management; (vi) agroforestry; and (vii) land-cover (use) change.
Grazing-land management and pasture improvement	Practices that reduce greenhouse gas emissions and enhance carbon uptake in grazing land include: (i) changes in grazing intensity; (ii) increased productivity (including use of fertilizer); (iii) improved nutrient management; (iv) fire management; and (v) species introduction.
Management of organic soils	Emissions on drained organic soils can be reduced to some extent by practices that include: (i) avoiding row crops and tubers; (ii) avoiding deep ploughing; and (iii) maintaining a shallower water table. The most important mitigation practice, however, will be not to drain these soils in the first place, or re-establishing a high water table where greenhouse gas emissions are still high.
Restoration of degraded lands	Storage of carbon in degraded soil can partly be restored by practices that improve productivity. These include: (i) revegetation; (ii) improving soil fertility by nutrient amendments; (iii) applying organic substrates; (iv) reducing tillage and retaining crop residues; and (v) conserving water.
Livestock management	Practices for reducing methane (CH4) emissions from livestock fall into three general categories: (i) improved feeding practices; (ii) use of specific agents or dietary additives; and (iii) longer-term management changes and animal breeding.
Manure management	Some options to mitigate the emission of nitrous oxide (N2O) and methane (CH4) during storage of manure include: (i) cooling or covering the stored manure; (ii) anaerobic digestion of manure to maximize retrieval of methane (CH4) as an energy source; (iii) storing and handling the manure in solid form; and (iv) altering livestock feeding practices.
Bioenergy	Agricultural crops and residues can be used as sources of energy and can replace fossil fuels. These products can be burned directly or can be further processed to generate liquid fuels such as ethanol or biodiesel. There will, however, be trade-offs with other land uses, such as food production, biodiversity, conservation and carbon sequestration. These have not been adequately studied.
Source: Smith et al. (2008).