If you have not followed issues concerning greenhouse gas (GHG) emissions, it's time to start. The EPA has proposed that atmospheric greenhouse gases endanger the health and welfare of current and future generations.

For agriculture, the top three gases of importance are nitrous oxide, methane and carbon dioxide, accounting for 45%, 38% and 17% of GHG from U.S. agriculture, respectively.

EPA Administrator Lisa Jackson commented that EPA's action will jump start a legislative solution to replace the need for regulation and that these pollutants are clearly impacting humans' lives and the EPA has the authority to intervene.

The recent EPA document, Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act, identifies these six atmospheric gases as the primary causes of global warming, attributable to human activity (in order of importance):

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous oxide (N2O)
  • Hydrofluorocarbons
  • Perfluorocarbons
  • Sulfur hexafluoride

A case is made that many of these GHG concentrations have increased considerably in recent decades. The EPA document ranks the U.S. second behind China in GHG emissions – 18% and 19%, respectively – of the world's total. It was also noted that U.S. net GHG emissions increased by 15% over the period 1990-2006, and that 13% of total U.S. GHG emissions were offset by net sequestration (carbon accumulation in the soil) due to land use, land use change and forestry. Global GHG emissions increased 26% between 1990 and 2005. The document noted that the six gases will be considered by their relative GHG value all in carbon dioxide equivalents; for example, one unit of methane is equivalent to 23 units of carbon dioxide and one unit of nitrous oxide is equivalent to 296 units of carbon dioxide.

The EPA document says that the increased carbon dioxide levels may boost a few crops’ yields in the very short term, but the impact of severe weather, poor moisture distribution and increasing temperature will have a long-run negative impact on yields and agricultural productivity.

Nitrous oxide emissions were attributed to agriculture soil management (72%) and motor vehicles and engines (8%). Emissions from engines and vehicles were noted to have declined due to tighter emissions standards. The report includes many other references to contributors to the top-six GHG and progress, or lack of progress, toward reducing their concentrations over time.

Some areas of agriculture are emitters and others are potential sinks. Nitrogen (N) application practices and manure management systems are GHG emitters. Practices to reduce nitrous oxide and methane emissions are already available to producers, and some incentives are in place to promote their use. The potential to sequester carbon in the soil trough tillage and/or alternative crops represents the other (positive) side of the coin.

The good news is that for the three significant areas just mentioned, we already have technologies online and in the pipeline to reduce GHG and to increase soil carbon. You may already know what is missing: economic incentive. We can point to some fairly soft incentives such as how increased soil carbon can benefit crop yields due to better soil moisture holding capacity and better soil structure. In the long run, increased soil organic matter can even improve the soils’ ability to exchange primary nutrients. Use of N stabilizers can increase N fertilizer and manure use efficiency, thus saving money on fertilizer and increasing yields. Livestock producers can utilize improved manure handling to capture methane and use it for power generation; this solution is most viable for larger producers who can capture their manure. Often times, these are dairy and swine operations. Some of all these practices are already in the field or on the farm, but to move them significantly ahead, we will either need a bigger carrot or a stick. Most of us don't like the stick idea!

While GHG are most often measured in carbon dioxide equivalents, the fact is that U.S. agriculture's contribution typically comes in the form of nitrous oxide and methane. In fact, agriculture's carbon dioxide contribution to total U.S. carbon dioxide emissions (not carbon dioxide equivalents) is about 1%, whereas agriculture accounts for over one-third of total methane emissions and over 70% of total nitrous oxide emissions. Increased corn acreage in recent years has increased GHG from agriculture due to the crops’ need for significant amounts of applied N fertilizer. Nitrogen fertilizer is both energy-intensive to produce and also increases the emissions of nitrous oxide. Livestock manure and stomach gases from cattle account for a large portion of the methane. One thing to keep in mind is that some of the methods to reduce GHG from agriculture can be capital-intensive in that they may require new equipment or significant modifications to existing facilities; such is the case for methane digesters for livestock manure.

IHS Global Insight is an economic research, forecasting and consulting firm headquartered in Lexington, MA.

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