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Accounting for increasing energy use by the US food system

May 25, 2010

Change in U.S. total and food system energy consumption over two five-year periods (1997-2002 and 2002-2007). Figure from Canning et al., 2010. Click image for report.

Energy used by the US food system accounted for 80% of the increase in American energy use between 1997 and 2002, according to a recent report from the USDA’s Economic Research Service. Other remarkable conclusions of the analysis include:

  • Food system energy use increased by 22.4% while total energy use rose by just 3.3%.
  • On a per capita basis, total energy use actually fell by 1.8%, but food system energy use was still up by 16.4%.
  • Putting food on the plate of the average American required 2.4 million BTU more in 2002 than in 1997. (To put this in context, total per capita energy consumption of 20 nations was less than 2.4 million BTU in 2002.)
  • The period between 2002 to 2007 likely saw another jump in food system energy use that far exceeded the increase observed in the rest of the US economy.

How does the way we eat have such a big effect on the amount of energy we use? According to this report, about half of the change is due to increased use of labor saving devices, with the remainder being split between population growth and changing food choices.  Fewer people are farming, processing, cooking, and cleaning. Machines do the work for us, and consume more energy to do it.

The report cites the following examples:

  • Between 1996 and 2006 farm labor use fell by nearly 30%, while farm equipment use increased by 10%;
  • 16,000 fewer people were employed in food preparation in 2000 than in 1996, but 4,800 more got jobs in food manufacturing;
  • The average time spent cooking and cleaning fell from 65 minutes to 31 minutes between 1965 and 1995.

Household energy use was the biggest slice of the food system energy pie in both 1997 and 2002, followed by wholesale/retail, processing, and farming. Transportation was the smallest segment, followed by packaging and food services. Growth in energy consumption was fastest in the processing and food services sectors. The wholesale/retail segment was distinguished as the only area in which energy use declined.

Where did the energy go? U.S. food system energy use by stage of production in 1997 and 2002 (bars), with percent change over the five year period (diamonds). Figure from Canning et al., 2010. Click image for report.

About a quarter of electricity used in US homes went to food-related services, including refrigeration (14%), cooking (6.5%), freezing (3.5%), and dishwashing (2.5%). This quantity increased as more households chose to buy second refrigerators, self-cleaning ovens, and other energy-demanding labor saving devices. Vehicle trips to the grocery store were counted as a household energy expenditure, rather than a transportation system expenditure.

Where did the extra energy go?

Where did the extra energy go? Changes in food system energy flow per capita, by food category, 1997-2002.

What we eat matters. Non-essential foods — alcoholic beverages, baked goods, snack foods, and pet foods — accounted for the biggest component of the increase observed between 1997 and 2002. The amount of energy used to get fresh fruits and vegetables to our plates also increased as we opted for pre-cut portions and convenience packaging.

The report notes that we can save energy by choosing fish over red meat, but cautions that our fisheries may not be able to sustain a large-scale increase in fish consumption. If aquaculture becomes increasingly necessary to satisfy demand for fish then much of the energy savings associated with wild-caught fish will be lost.

The report calls for food prices to accurately reflect energy consumption throughout the supply chain, to signal consumer choices that reduce energy use as energy prices rise.

8 Comments leave one →
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  3. October 7, 2010 9:12 am

    The September issue of Amber Waves offers a nice summary of the study discussed in this post. The online version features a streamable interview with the study’s lead author, Patrick Canning. See

  4. Lula permalink
    June 1, 2010 10:07 am

    I found this interesting. Having read about another report “Livestock and Climate Change” by Goodland and Anhang (co-authors), in terms of greater energy expenditure and worldwide GHG emissions, it is not clear to me how these two reports and their figures relate. It seemed that they should both be considered. Here is the link to “Livestock and Climate Change” report.

    • June 1, 2010 11:40 am

      This report from USDA’s Economic Research Service looks at the change in energy consumed by the US food system between 1997 and 2002. The “Livestock and Climate Change” report published by the Worldwatch Institute attempts to account for global greenhouse gas emissions from livestock alone. Energy use and greenhouse gas emissions are strongly correlated in most sectors of the economy, but not in agriculture. Greenhouse gas emissions from agriculture are more likely to be associated with methane and nitrous oxide production related to animal and soil management practices than with carbon dioxide production from burning fossil fuels for energy. The USDA analysis is in line with previous research in concluding that agricultural energy use is a small proportion (~2%) of national energy use. It doesn’t attempt to calculate agriculture or food system greenhouse gas emissions, and its scope is limited to the USA, not the planet.

      I read the “Livestock and Climate Change” report soon after it was issued, and was disappointed by several conclusions that appear to be based on flawed assumptions and faulty logic. This surprised me, because I am usually impressed with articles from Worldwatch. “Livestock and Climate Change” is a response to a UN Food and Agriculture Organization (FAO) report called “Livestock’s Long Shadow” which estimates that livestock are responsible for 18% of global greenhouse gas emissions. The FAO didn’t soft-pedal livestock’s impact, concluding that livestock account for about a third of global methane emssions and two-thirds of nitrous oxide emissions.

      The Worldwatch report includes animal respiration as a source of carbon dioxide emissions, but the FAO report does not. I tend to agree with the logic of the FAO that respiration is not a net source of CO2. The Worldwatch report’s claim that “a molecule of CO2 exhaled by livestock is no more natural than one from an auto tailpipe” appears to ignore the fact that livestock eat plants and automobiles consume fossil fuels.

      The Worldwatch report misinterprets a questionable conclusion by British physicist Alan Calverd that 21% of CO2-producing power consumption involves keeping farm animals. This gets turned into a claim that livestock respiration accounts for 21% of human CO2 emissions.

      I think that the Worldwatch report’s argument that the FAO’s analysis of carbon release from land clearing for livestock should include foregone greenhouse gas reductions is equally suspect. When I calculate how much I spend each month should I include all of the money that I didn’t make? An economist might argue that I should, and call the foregone income “opportunity cost,” but that doesn’t help with my budgeting. If we’re making claims about greenhouse gas emissions I think we should stick to actual emissions.

      The most interesting thing about the Worldwatch report is its discussion of methane. Whether we choose to look at the global warming potential of methane over a 20 or 100 year timeframe is a political question with enormous implications. On a 20 year timeframe the apparent potency of methane triples. Livestock are the single biggest contributor to anthropogenic methane, and atmospheric methane is up by 150% since pre-industrial times whereas CO2 is only up 31%. (But atmospheric methane concentration is leveling off while CO2 concentration continues to rise).

      It’s a bit fishy to use the 20 year multiplier for livestock emissions and not for other methane emissions, especially when stating livestock emissions as a proportion of greenhouse gas emissions. Still, the methane issue is worth delving into. I think the World Watch report would have been much stronger if it had stuck with methane and avoided the other arguments, which are too-easily dismissed.

      The World Watch report may be correct in claiming that the FAO underestimated livestock contributions to greenhouse gas emissions, but I think that its own estimate is far less credible than the FAO’s.


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