Mitigation technologies, practices, options, potentials and costs

Considering all gases, the economic potentials for agricultural mitigation by 2030 are estimated to be about 1600, 2700 and 4300 MtCO₂-eq/yr at carbon prices of up to 20, 50 and 100 US$/tCO₂-eq, respectively for a SRES B2 baseline (see Table TS.11) (medium agreement, limited evidence) [8.4.3].

Improved agricultural management can reduce net GHG emissions, often affecting more than one GHG. The effectiveness of these practices depends on factors such as climate, soil type and farming system (high agreement, much evidence).

About 90% of the total mitigation arises from sink enhancement (soil C sequestration) and about 10% from emission reduction (medium agreement, medium evidence). The most prominent mitigation options in agriculture (with potentials shown in Mt CO₂eq/yr for carbon prices up to 100 US$/tCO₂-eq by 2030) are (see also Figure TS.20):

• restoration of cultivated organic soils (1260)
• improved cropland management (including agronomy, nutrient management, tillage/residue management and water management (including irrigation and drainage) and set-aside / agro-forestry (1110)
• improved grazing land management (including grazing intensity, increased productivity, nutrient management, fire management and species introduction (810)
• restoration of degraded lands (using erosion control, organic amendments and nutrient amendments (690).

Figure TS.20: Potential for GHG agricultural mitigation in 2030 at a range of carbon prices for a SRES B2 baseline [Figure 8.9].

Note: B2 scenario shown, though the pattern is similar for all SRES scenarios. Energy-efficiency measures (770 MtCO₂-eq) are included in the mitigation potential of the buildings and energy sector.

Lower, but still substantial mitigation potential is provided by:

• rice management (210)
• livestock management (including improved feeding practices, dietary additives, breeding and other structural changes, and improved manure management (improved storage and handling and anaerobic digestion) (260) (medium agreement, limited evidence).

In addition, 770 MtCO₂-eq/yr could be provided by 2030 by improved energy efficiency in agriculture. This amount is, however, for a large part included in the mitigation potential of buildings and transport [8.1; 8.4].

At lower carbon prices, low cost measures most similar to current practice are favoured (e.g., cropland management options), but at higher carbon prices, more expensive measures with higher mitigation potentials per unit area are favoured (e.g., restoration of cultivated organic / peaty soils; Figure TS.20) (medium agreement, limited evidence) [8.4.3].

GHG emissions could also be reduced by substitution of fossil fuels by energy production from agricultural feedstocks (e.g., crop residues, dung, energy crops), which are counted in energy end-use sectors (particularly energy supply and transport). There are no accurate estimates of future agricultural biomass supply, with figures ranging from 22 EJ/yr in 2025 to more than 400 EJ/yr in 2050. The actual contribution of agriculture to the mitigation potential by using bioenergy depends, however, on the relative prices of fuels and the balance of demand and supply. Top-down assessments that include assumptions on such a balance estimate the economic mitigation potential of biomass energy supplied from agriculture to be 70–1260 MtCO₂-eq/yr at up to 20 US$/tCO₂-eq, and 560–2320 MtCO₂-eq/yr at up to 50 US$/tCO₂-eq. There are no estimates for the additional potential from top-down models at carbon prices up to 100 US$/tCO₂-eq, but the estimate for prices above 100 US$/tCO₂-eq is 2720 MtCO₂-eq/yr. These potentials represent mitigation of 5–80%, and 20–90% of all other agricultural mitigation measures combined, at carbon prices of up to 20, and up to 50 US$/tCO₂-eq, respectively. Above the level where agricultural products and residues form the sole feedstock, bioenergy competes with other land-uses for available land, water and other resources The mitigation potentials of bioenergy and improved energy efficiency are not included in Table TS.11 or Figure TS.20, as the potential is counted in the user sectors, mainly transport and buildings, respectively (medium agreement, medium evidence) [8.4.4].

The estimates of mitigation potential in the agricultural sector are towards the lower end of the ranges indicated in the Second Assessment Report (SAR) and TAR. This is due mainly to the different time scales considered (2030 here versus 2050 in TAR). In the medium term, much of the mitigation potential is derived from removal of CO₂ from the atmosphere and its conversion to soil carbon, but the magnitude of this process will diminish as soil carbon approaches maximum levels, and long-term mitigation will rely increasingly on reducing emissions of N₂O, CH₄, and CO₂ from energy use, the benefits of which persist indefinitely (high agreement, much evidence) [8.4.3].