Middlebury, Vt.

Life in the middle of Vermont.

Thursday, January 11, 2007

Cheeseburgers & Global Warming

Cattle are a major source of methane, a greenhouse gas. Producing a burger from a cow also cause emisisons -- all of which caused one blogger at http://www.openthefuture.com to tote it up:

The Footprint of a Cheeseburger
I wondered a couple of days ago what the carbon footprint of a hamburger might be. It's the kind of question we'll be forced to ask more often as we pay greater attention to our individual greenhouse gas emissions. Burgers are common food items for many people; it's said that the average American eats three burgers per week, or about 150 burgers per year. What's the global warming impact of all that? I don't just mean cooking the burger; I mean the gamut of energy costs associated with a hamburger -- including growing the feed for the cattle for beef and cheese, growing the produce, storing and transporting the components, as well as cooking.
The clues provided by my friends Martin Kelly and Kim Allen sent me looking in the right direction, but then I stumbled across an absolute treasure: Energy Use in the Food Sector (PDF), a 2000 report from Stockholm University and the Swiss Federal Institute of Technology, looking at the life cycle energy use associated with... a cheeseburger! This highly-detailed report covers the myriad elements going into the production of the components of a burger, from growing and milling the wheat to make bread, to feeding, slaughtering and freezing the cattle for meat -- even the energy costs of pickling cucumbers. The report is fascinating in its own right, but it also gave me exactly what I needed to make a relatively decent estimation of the carbon footprint of a burger.
Based on a variety of sources, the researchers conclude that the total energy use going into a single cheeseburger amounts to somewhere between about 7 and 20 megajoules -- the range comes from the variety of methods available to the food industry.
The researchers break this down by process, but not by energy type. Here, then, is my first approximation: I split the food production and transportation uses into a diesel category, and the food processing (milling, cooking, storage) uses into an electricity category. Split this way, the totals add up thusly:
Diesel -- 4.7 to 10.8 MJ per burgerElectricity -- 2.6 to 8.4 MJ per burger
With these ranges in hand, I could then convert the energy use into carbon emissions, based on fuel. For electricity, I calculated the footprint using both natural gas and coal; if you're lucky enough to have your local burger joint powered by a wind farm, you can drop that part of the footprint entirely.
Diesel -- 90 to 217 grams of carbon per burgerGas -- 37 to 119 grams of carbon per burgerCoal -- 65 to 209 grams of carbon per burger
...for a combined carbon footprint of a cheeseburger of 127 grams of carbon (at the low end, with gas) to 426 grams of carbon (at the high end, with coal). Adding in the carbon from operating the restaurant (and driving to the burger shop in the first place), we can reasonably call it somewhere between a quarter-kilogram and a half-kilogram of carbon emissions per cheeseburger. (But see below...)
Or, over the course of a year, between 37 and 75 kilograms of carbon emissions from the average American's cheeseburger habit.
If each of the 300 million Americans hit that "average" burger consumption, we're looking at 75,000-150,000 tonnes of atmospheric carbon annually from burger consumption alone -- that's the equivalent of the annual carbon output from 7,500-15,000 SUVs.
[But see below...]
(Update: I was reminded in email (thanks, Geoff!) that this should also include the methane emissions from cattle. So, let's add that.)
A typical beef cow produces approximately 500 lbs of meat for boneless steaks and ground beef. By regulation, a beef cow must be at least 21 months old before going to the slaughterhouse; let's call it two years. A single cow produces 114 kilos of methane per year in eructations and flatulence, so over its likely lifetime, a beef cow produces 228 kilos of methane (not including the methane from its manure). Since a single kilo of methane is the equivalent of 23 kilos of carbon dioxide, a single beef cow produces 5244 CO2-equivalent kilograms of methane over its life. If we assume that the typical burger is a quarter-pound of pre-cooked meat, that's 2,000 burgers per cow. Dividing the methane total by the number of burgers, then, we get about 2.6 CO2-equivalent kilograms of additional greenhouse gas emissions from methane, per burger, or about 5-10 times more greenhouse gas produced from cow burps than from all of the energy used to raise, feed or produce all of the components of a completed cheeseburger!
At 2.85-3.1 kg of CO2 (equiv) per burger, then, that's 428-465 kg of greenhouse gas per year for an average American's burger consumption.
(Second Update: More details on methane output from ruminants like cattle, courtesy of the EPA. The government estimates for methane output from "enteric fermentation" is a bit lower than the number cited in the Telegraph article, but when we add in the methane from manure -- which is about a third of that from cattle gas -- the overall numbers I've used still roughly work out.
And to add the necessary correction: adding in the methane, the overall CO2-equivalent emissions from all the cheeseburgers consumed in the US (assuming the average of 3/person is accurate) roughly equal the greenhouse output of 100,000 SUVs.
Obviously, these are all estimates, and will vary considerably by individual cow, feed type, and other environmental conditions -- but assuming my sources are correct, these methane outputs should be roughly accurate, enough to trigger a good conversation, at least.)