Greenhouse Emissions of Agriculture
In the last blog there was a comment by peregrinepickle on the emissions from agriculture. It started:
“It sounds like they may be putting the cart before the workhorse with this study. A 2010 survey of the literature found that too few studies on GHG emissions and the impact of various alternative farming practices have been done in US agricultural regions, including the Great plains Ironically, more research is being done in this vein in China. So it seems premature to appeal to US farmers re: willingness to adopt certain practices before knowing exactly where you are going with it.
Agriculture, compared to other sources, is not a huge contributor to GHGs, relative to the contributions by industry, transportation, and utilities. In the US farming is responsible for 6% of the overall emissions of the six major GHGs. However, farming does contribute about 25% of all CH4 emissions in the US, which is major, as this gas is 21-33 times more potent in warming potential than CO2.”
Back in April and May I wrote two entries on the emissions from agriculture (first entry
, second entry
). These two entries highlighted both the complexity of calculating the greenhouse emissions related to agriculture as well as suggested some of the controversy associated with the calculation. The controversy is especially high in the calculation associated with livestock.
The amount of direct fossil fuel emissions from use of fuels in machinery and pumps for agriculture is modest, as stated in peregrinepickle’s comment. Those numbers are based on a 2010 inventory by the Environmental Protection Agency
. Here is a link to the chapter that details the agricultural inventory
. The greenhouse gas emissions compiled in the chapter on agriculture are for greenhouse gases other than carbon dioxide, especially methane and nitrous oxide. For the EPA inventory, the carbon dioxide associated with agriculture is accounted for in the energy inventory
. Additional emissions and removal of greenhouse gasses are calculated with land use, land change and forestry
. The national forests
are part of the Department of Agriculture
The accounting with soils and forests influences, greatly, the budget of emissions associated with agriculture. Based on soil management agriculture can remove and store substantial amounts of greenhouse gases. In the U.S. agriculture is a mature and extensive enterprise, and we are not aggressively converting forest to agricultural land. In fact, the amount of forest is increasing and, therefore, can be accounted as an agricultural removal of carbon dioxide. This fact of increasing forest land is not the case in much of the world. World-wide, deforestation as forest is converted to agricultural use, especially rangeland, accounts for much of the carbon footprint
of agriculture. Phil Robertson
in an article to appear in the Encyclopedia of Agriculture estimates the total greenhouse gas footprint of agriculture is between 26 and 36 percent (thank you Professor Robertson). This range seems soundly based in the synthesis of research, and the number I would quote based on the current state of knowledge.
As detailed in Livestock’s Long Shadow
and stated in the entirety of peregrinepickle’s comment, the impact of agriculture reaches far beyond the relevance to climate change. Notably there are impacts on water quality and land quality, and, in my opinion, the impact of nitrogen (fertilizer) pollution is one of the most under appreciated sources of environmental degradation. Management of this whole portfolio of environmental impacts is one of the special challenges of the agricultural sector of human activities.
The mix of greenhouse gas emissions, the details of the practice of land use, the role of biological processes, and the potential to remove greenhouse gases from the atmosphere and store them in soil and biomass characterize the climate impact of agriculture. Agriculture is also vulnerable to climate change. Since agriculture is a highly competitive, market-dependent undertaking, market response to weather and climate can amplify weather-related impacts. Agriculture becomes more entangled with the climate problem, when we consider the possibility of biofuels to replace some of our fossil fuels. This complexity complicates the accounting of climate impacts, but also offers some of our best opportunities to improve our management of the environment. Agriculture is no doubt an important player in our management of climate change, and notably absent in President Obama recent speech on climate change
A primary source of agricultural information is Food and Agriculture Organization of the United Nations
. An often cited document is the 2006 documentLivestock’s Long Shadow
. There has been much criticism of this report, especially in its calculation of the emissions of the transportation sector. The original authors did modify their specific statements about transportation
. As noted in an earlier blog in this series
, there is substantial controversy about the impact of agriculture. Therefore, I end here with a set of reference materials that I have used.EPA National Greenhouse Gas Emissions DataPDF of Agriculture Chapter of EPA Inventory of EmissionsAgriculture’s Role in Greenhouse Gas EmissionsFood and Agriculture Organization of the United NationsChapter 8: Working Group 3: IPCC 2007Energy Efficiency of Conventional, Organic and Alternative Cropping …Livestock and Climate Change
and to appear
Soil Greenhouse Gas Emissions and their Mitigation, G. Philip Robertson, W.K. Kellogg Biological Station and the Department of Plant, Soil and Microbial Sciences, Michigan State University, Hickory Corners, MI 49060