Agriculture’s role in greenhouse gas mitigation

Sep 2006

Since the 1940s, the emergence of modern agriculture has dramatically altered the relative sources and amounts of agricultural GHG fluxes. Increasing productivity, improved cropping practices, erosion control measures, and reduced tillage intensity (see Chapter II) have stabilized and begun to rebuild the organic carbon stocks of many agricultural soils. As a result, on a net basis, the US croplands currently remove more CO2 from the atmosphere than they release to it; and they now act as a net sink for CO2. Reforestation of marginal agricultural lands, particularly in the East, has also contributed to the present carbon sink attributed to US. forestland (USEPA 2006). On the other hand, the development and growing use of industrial fertilizers over the past 50 years has greatly increased the input of nitrogen to soils, resulting in nitrogen losses to the environment in various forms, as among which nitrous oxide emissions. Growth in livestock numbers, particularly within large, confined operations, has increased emissions of methane from livestock and manure over the same period.
Crop yields increases, along with continued adoption of conservation tillage and maintenance of conservation set-aside programs, are likely to support further increases in soil carbon stocks. Higher crop yields also increase the potential for shifting some land from food production to energy crop production.
As detailed in the following chapters, the current technical potential to mitigate GHGs through improved agricultural practices over the next 10 to 30 years is substantial, estimated at approximately 102 to 270 MMT carbon-equivalent per year. This estimate derives from a combination of carbon sequestration, nitrous oxide reductions, and methane reductions. In addition, energy produced from agricultural biomass sources, if substituted for fossil fuels, represents a mitigation potential of 510 to 1,710 MMT CO2-equivalent per year or 7 to 24 percent of total 2004 U.S. GHG emissions (see chapter IV). However, the mitigation levels that can be achieved economically are likely to be substantially lower than these technical potentials.
As discussed in chapter III, a variety of economic and social factors will influence the adoption of alternative practices and production systems, although studies to date suggest that a significant portion of agricultural mitigation practices can be characterized as low-cost options (i.e., relative to many mitigation options in energy, industry, transportation, etc). Further, chapter IV points out that significant research efforts to reduce biofuel conversion costs and increase energy crop yields would be needed for biofuels to reach their full mitigation potential. Finally, changes in land use and management to achieve GHG mitigation can contribute to overall environmental improvements. Hence, a broader consideration of the costs and benefits of improved agricultural practices, beyond the realm of climate change concerns, is merited.
The practices that could be implemented to stimulate GHG mitigation, the resulting economic opportunities, a review of biofuel options, and the policy implications of these opportunities are discussed in the following chapters.

By: K. Paustian, J. M. Antle, J. Sheehan, E. A. Paul (Pew Center)

 
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