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United States Department of Agriculture

Agricultural Research Service

Title: Strategies and Economics for Greenhouse Gas Mitigation in Agriculture

item Dumanski, Julian - RETIRED SOIL SCIENTIST
item Desjardins, R - AG AND AGRI-FOOD
item DE Freitas, Pedro - EMBRAPA SOILS
item Landers, John - APDC BRAZIL
item Gerber, Pierre - FAO
item Steinfeld, Henning - FAO
item Verchot, Louis - CIFOR
item Schuman, Gerald - RETIRED SOIL SCIENTIST
item Derner, Justin

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: June 9, 2009
Publication Date: July 2, 2010
Citation: Dumanski, J., Desjardins, R.L., Lal, R., De Freitas, P.L., Landers, J.N., Gerber, P., Steinfeld, H., Verchot, L., Schuman, G.E., Derner, J.D. 2010. Strategies and Economics for Greenhouse Gas Mitigation in Agriculture. In: Stigter, K. (ed.), Applied Agrometeorology. Springer, Heidelberg, Germany. pp 1101. Book Chapter.

Technical Abstract: INTRODUCTION Agriculture can make significant contributions to climate change mitigation by a) increasing soil organic carbon sinks, b) reducing GHG emissions, and c) off-setting fossil fuel by promoting biofuels. The latter has the potential to counter-balance fossil-fuel emissions to some degree, but the overall impact is still uncertain compared to emissions of non-CO2 GHGs, which are likely to increase as production systems intensify. Agricultural lands also remove CH4 from the atmosphere by oxidation, though less than forest lands (Tate et al., 2006; Verchot et al., 2000), but this effect is small compared to other GHG fluxes (Smith and Conen, 2004) The main GHGs from agriculture are CO2, CH4, and N2O, and collectively these account for 10- 20 % of the annual increase in radiative forcing, and up to one third when land use change is included (IPCC, 2007). Agriculture accounts for between 59 and 63 % of the world’s non-CO2 GHG emissions, including 84 % of the global N2O emissions and 54 % of the global CH4 emissions (USEPA, 2006). Of these, N2O emissions from soils are the most important, followed by CH4 from enteric fermentation. Methane from rice cultivation is the third largest source. Deforestation is another major source of GHG emissions (about 7.6 Pg CO2 e/ yr). Direct emissions from fossil fuel account for about 10 % from this sector (Verchot, 2007). Non-CO2 GHG emissions from agriculture are expected to increase significantly in the future, with soil emissions of N2O (75 %) and CH4 from enteric fermentation (70 %) being the largest sources. Enteric fermentation and emissions from manure are expected to increase significantly, and become about 50 % greater than in 1990 (USEPA, 2006). These emissions are driven by production pressures, which in turn are driven by global processes such as world population density, globalization, urbanization, increased purchasing power of the middle classes, etc (Dumanski, 2008). Increased consumption of meat products as societies become more affluent is an important driver for emissions from enteric fermentation. All of these are expected to increase in the future, particularly in tropical countries. STRATEGIES FOR MITIGATING GHG EMISSION IN AGRICULTURE Recently, there have been significant improvements in farm management practices with a resulting increase in the carbon efficiency of agricultural production. Notably, while N2O and CH4 emissions have increased because of increasing levels of food production, the GHG emissions per unit of production have decreased. In Canada for example, GHG emissions per kilogram of beef cattle live weight have decreased from 13.9 to 10.4 kg CO2e from 1991 to 2006 (Verge et al., 2008a). During the same period, the GHG emission intensities for pork and poultry have decreased by 29 and 16% respectively (Verge et al 2008 b,c). Mitigation of climate change in agriculture requires adoption of integrated farming systems, since these capture the synergy of multiple practices and have the potential to reverse the decline and actually increase the soil organic carbon pool. Practices such as zero tillage (ZT) have the combined effect of soil carbon sequestration while concurrently reducing fossil fuel use and improving biodiversity. Other mitigation measures include agronomic practices such as improved crop varieties, improved crop rotations, and improved fertilizer management. Better residue and water management in rice can yield significant reductions of CH4 emissions. For livestock, there are a wide range of practices associated with grazing land management, improved feeding, and manure management that can reduce emissions and increase carbon sequestration. The collective impact of these practices is to reduce GHG emissions and sequester carbon in the soil. The IPCC (2000) identified three land use systems with significant global potentials for climate change mitigation, agroforestry, improved grassland management, and restoration of severely degraded lands. Verchot (2007) evaluated these options, and identified agroforestry and grassland management as the best options. Agroforestry involves the integration of trees into farming systems and agricultural landscapes, including the conversion of slash-and-burn to agroforests after deforestation, as well as conversion from low-productivity croplands to sequential agroforestry. Agroforestry has such a high potential because it is the land use category with the second highest carbon density after forests, and because there are large area suitable for such land use systems. Improved grassland management, despite the low carbon densities in this land use system, has a high potential because of the large land areas suitable for these improvements (3.4 billion ha). Improved carbon sequestration in grasslands can be achieved through introduction of more productive grass species and legumes, improved livestock management, proper stocking and improved nutrient management. About 60 % of the grazing lands suitable for improved carbon sequestration are in developing countries (Verchot, 2007). These land use systems are also effective in helping small scale farmers adapt to climate change, because they reduce their vulnerability to inter-annual weather variability and changing climatic conditions. Rehabilitation of degraded land and wetland restoration are very expensive, and globally they have limited potential for climate change mitigation, although they may have significant local benefits. Attention has recently focused on the role of agriculture to supply biomass for the production of ethanol and bio-diesel. These are renewable energy sources with the potential to reduce emissions from fossil fuels, but there are concerns regarding the carbon efficiency of the process as well as possible negative impacts on soil erosion if residues are used for biofuels. ECONOMIES OF GHG MITIGATION IN AGRICULTURE The Stern Review (Stern, 2007) estimates that global mitigation of GHGs emissions can be achieved with as little as 1 % of global GDP if action is taken immediately. This, however, requires strong policy signals, including pricing of carbon (implemented through tax, trading or regulation), support for innovation and low-carbon technologies, and removal of barriers to energy efficiency. Although emphasis has to be on reductions in the power sector and transport, cuts in non-energy emissions, such as those resulting from deforestation and from agricultural and industrial processes, are also essential. While not as large as the potential from the power sector and transportation, the total potential savings from various agricultural and land use change activities are still substantial, and they can be achieved at a competitive cost. Mitigation of GHG in agriculture involves emission reductions, as well as carbon sequestration. Verchot (2007) estimates that some emission reductions can be achieved with no increase of implementation costs. Globally, approximately 7 % of the net emissions from agriculture can be mitigated at a net benefit or at no cost (< $0/t CO2e), including approximately 15 % from croplands, approximately 3 % from rice cultivation, and 6 % from animal production. The mitigation potentials increase somewhat with an increase in the price of carbon. Approximately 20 % of agricultural emissions can be mitigated as carbon prices approach $30/t CO2e (Verchot, 2007). Beyond this point, the returns on investment decrease rapidly, suggesting that there are a few opportunities for greater reductions at higher carbon prices. The greatest potentials for negative and low-cost reductions are in the Russian Federation, non-OECD countries, Australia/New Zealand, and the United States, with only moderate potential in most other countries. Achieving significant carbon mitigation in developing countries will require tapping carbon offsets from agriculture and land use change. With as much as 13 Gt of CO2 per year at prices of US$10–20/t, this repr

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