Note to Editors: The full report is available at http://www.pewclimate.org/global-warming-in-depth/all_reports/agriculture_s_role_mitigation/index.cfm.
Changes in agricultural practices across the nation could offset up to one-seventh of current greenhouse gas emissions in the United States and has the potential to further reduce emissions by replacing fossil fuels with biofuels made from agricultural crops, according to a Colorado State University researcher’s recent Pew Center on Global Climate Change report.
According to Keith Paustian, professor and senior research scientist at Colorado State’s Natural Resource Ecology Laboratory, and fellow co-authors of the report, "Agriculture’s Role in Greenhouse Gas Mitigation," a combination of carbon sequestration in agricultural soils and a reduction in nitrous oxide and methane emissions from agricultural sources would allow the United States to reduce its current greenhouse gas emissions by 6 percent to 14 percent.
Additionally, as the development of agricultural biofuels is pursued and further developed, another 14 percent to 24 percent of current emissions in the country could be eliminated by substituting biofuels for fossil fuels. Potentially, the agricultural industry in the nation could reduce emissions by 20 percent to 38 percent.
"There are no simple solutions to the global warming problem, but the agricultural community can make a major contribution, which is often overlooked," Paustian said.
Farmers would be encouraged to adopt new management practices to store carbon in agricultural soils and reduce agricultural emissions of methane and nitrous oxide. Financial incentives are needed but also better access to financing, information and education. A variety of technological advancements will also affect farmers’ ability to play a part in climate solutions.
The agriculture industry in the United States contributes only about 8 percent to the nation’s emissions, but the influential role agriculture could play in mitigating greenhouse gas emissions is its ability to remove carbon dioxide from the atmosphere and produce feedstock for biofuels.
As plants take up carbon dioxide through the process of photosynthesis, some of the carbon is stored in organic matter found in soils and plants. With the right management, there is a build up of the carbon stored in soils and plants, termed carbon sequestration, so that carbon dioxide is effectively removed from the atmosphere.
There are several ways that farmers can implement specific management practices to increase carbon sequestration in agricultural soils and reduce the loss of carbon already in the soil. Suggested management practices include farmers using better crop rotations, reducing tillage intensity, putting marginal land into conservation reserves and improving the management of their pastures. By adopting these practices, additional environmental benefits are accrued including improved soil fertility, reduced soil erosion and improved water quality.
While the agriculture industry does not emit a large percentage of the nation’s greenhouse gases, two of the gases it does emit – methane and nitrous oxide – have a more powerful effect pound-for-pound on global warming. The primary way to reduce these emissions is by implementing more efficient use of fertilizers and manure and improving livestock managements. If farmers adopted these management practices, Paustian and his colleagues estimate that nitrous oxide and methane emissions could be reduced by 20 percent to 40 percent.
Another component of Paustian’s study examines the use and production of biofuels in America. Currently, about 5 percent of the United States’ energy supply comes from biomass. This includes ethanol from corn and biodiesel from soybeans and restaurant oil, as well as heat and power from biofuel in homes and industry.
With aggressive improvements in agricultural production and in the technology to convert biomass to energy, Paustian and his fellow researchers estimate that the nation’s agricultural industry could produce enough renewable bioenergy each year to supply one-fifth of the total energy consumed last year in the United States. All of this bioenergy would be produced on 15 percent of prime agricultural land.
Paustian cautions that if biomass is converted to transportation fuels, the greenhouse gas impacts vary depending on the amount and source of energy used to produce the biomass and convert it to fuels. Thus ethanol from corn grain is less effective in reducing overall greenhouse gases compared with biodiesel because of factors involved in growing and harvesting corn. Biodiesel is derived from vegetable oil, or so-called bioethanol, which is derived from crop residues and grasses.
"The big problem with using grain is that you use almost as much energy to produce the grain as you get out of the ethanol value. It’s not very energy efficient," said Paustian. "However, the cost of producing bioethanol from residues and grasses is currently higher than for corn ethanol, and thus more research and development is needed before bioethanol can play a major role as a renewable fuel."
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