The food eaten by a typical US household involves the creation of 8.1 tons per year of CO2-equivalent greenhouse gases, according to researchers at Carnegie Mellon University. [Link repaired 1/26/2011.] (Methane and nitrous oxide, which are also GHGs, are more important in the food chain than CO2 itself.) About 83 percent of the food-related GHGs are generated in the growing and harvesting of food, and about half of that is associated with red meat and dairy products. Only 11 percent of the GHGs are generated in transportation of food, with the 6-percent balance presumably associated with processing and packaging. In contrast, a typical automobile driven 12,000 miles per year at 25 MPG emits "only" 4.4 tons of CO2. I doubt the pending cap-and-trade legislation covers cows. Thanks to Ezra Klein's blog for this information. The graphic is from the CMU report.
In New Zealand, ruminants are by far the main contributor to GHGs, according to this LATimes piece.
On a per-pound basis, methane is 23 times more potent as a GHG than is CO2, and nitrous oxide is 310 times more potent. Where did we get the idea that global climate change is essentially a fossil fuels problem?
These gases didn’t pass my smell test. (Sorry about that.) So I’ve done some more research.
This EPA report contains detailed annual estimates of anthropogenic GHG emissions for, and according to the methods of, the United Nations Framework Convention on Climate Change, ratified by the US in 1992. In 2006, total GHG emissions in the US were 7,054 teragrams (“Tg”) of CO2-equivalents. This is 7,054 billion kilograms or 7,054 million metric tonnes. (With 110 million households in the US in 2006, this is 64.1 tonnes per household, somewhat larger than the 60 tonnes stated in the Science News piece about the CMU report, or 71.2 short tons of 2,000 pounds each.) All the following numbers except percentages are in teragrams.
Although methane and nitrous oxide (and a few other gases) are much more potent GHGs than CO2 on a pound-for-pound basis, they are emitted in relatively tiny amounts. So, even after multiplication by their potency factors, they account for only 15.2% of the total of CO2-equivalents. Actual CO2, at 5,983 Tg, is 84.8% of the total, and 94.2% of that (80.0% of the total CO2-equivalent emissions) comes from combustion of fossil fuels. So, at least with respect to the US’s contribution to global climate change, it definitely is essentially a fossil fuels problem, and the food and agriculture issue should be regarded as a distraction.
Farming does produce almost half of the non-CO2 GHGs. Of a total of 923 Tg-equivalents of methane and nitrous oxide emissions, 446 Tg (48.3%) are directly from agriculture, consisting of 265 Tg of nitrous oxide from “soil management” and 181 Tg of methane and nitrous oxide from digestive gases and “manure management.” (Note that more of the farm contribution is from fertilization practices than from ruminants.) Still the total of GHGs emitted directly from all farms is only 6.3% of the total of GHGs. For comparison, GHGs attributed to all highway use of gasoline and diesel fuel is 20.6% of the total (1,456 Tg). Thus, driving is more than 3 times as significant as eating, instead of only half as significant.
The Science News article says food accounts for 11% of total GHGs, but that evidently includes other processes like fertilizer manufacture, tractor fuel, electricity used in agriculture and food processing, etc. For that reason it is no more valid to compare the GHG cost of food with the GHG cost of driving a car than it would be to compare the GHG cost of the healthcare or financial sectors of the economy divided by the number of households with driving a car. I regret that I got mislead by the Science News article, and regret that I may have misled one or both of my readers.
Steven Budiansky makes the following points (and others) in this NYT op ed: Transportation accounts for only 14% of the total energy consumed in the American food system, while household food-related energy consumption (refrigeration, cooking, etc.) accounts for 32% of the total energy used in the food system. Budiansky says the locavore movement leads to counterproductive results if it causes tomatoes to be grown in heated New York greenhouses instead of transported into New York from California. Careful readers will have noticed that Budiansky did his calculations in energy units and that calculations in greenhouse gas emissions might lead to modestly different results. Budiansky presents more data and a graph in his related blog post, Local, Schmocal.