Saturday, August 20, 2011

Meat vs Gas Guzzlers

A sea change in the consumption of beef may be in store for Americans, according to a story by Mark Bittman in the New York Times in 2008 ( Such a change would impact the subject of two public policy discussions and political debates: energy consumption and carbon dioxide emissions. Bittman makes two claims about the energy use and emissions from beef relative to that of driving that are of particular interest.

Citing the National Institute of Livestock and Grassland Science in Japan, one of the Bittman's claims is that the emissions from the production of 2.2 pounds of beef is equivalent to the emissions from driving the average European car 155 miles. Let's see.

Information we have indicates that the average European car emits 140 grams CO2 per kilometer, that there are 453.59 grams of CO2 per pound, that there are .621 miles per kilometer, that the average US auto is driven 10,000 miles per year, has an average miles per gallon of 20, and emits 10,211 pounds CO2 per year (this figure, based on our estimated miles per year and miles per gallon, is lower than the 12,500 pounds CO2 figure provided by EPA).

Using these inputs, we find that driving a European auto 70.5 miles emits as much CO2 as one pound of beef. European autos emit CO2 at a rate of 0.309 pounds per kilometer, 0.497 pounds per mile, and 35.0 pounds per 70.5 miles. US Beef consumption per capita is 87.3 pounds, which results in 3,055 pounds of CO2, which according to this claim is the amount generated by driving a European vehicle 6,150 miles. US vehicles emit over twice as much CO2 per mile as do European vehicles, which means that driving 2,992 miles in a US vehicle generates this same amount of CO2.

We have no reason to doubt this claim. However, as for the impact on climate change of beef consumption versus driving, an important conclusion from these calculations is that total emissions from beef consumption are less than thirty percent of the total emissions from US average vehicle miles traveled (VMT). (This doesn't consider substitute effects, i.e., that people who give up beef will eat something else that generates emissions at some unknown lower rate, and that a reduction in VMT may result in an increased use of an alternate form of transit that likewise generates emissions at some unknown lower rate.)

Citing Gidon Eshel, a geophysicist at the Bard Center, and Pamela A. Martin, an assistant professor of geophysics at the University of Chicago, another of Bittman's claims is that the emissions reduction from a twenty percent reduction in beef consumption is equivalent to the emissions reduction that would be realized from switching from a standard sedan to the ultra-efficient Prius.

Using the estimate calculated above of 3,055 pounds CO2 per capita per year from beef consumption, a twenty percent reduction in beef consumption would reduce emissions by 611 pounds. A Prius gets 48 MPG and emits 4,807 pounds CO2 per year, compared to an Accord which gets 21 MPG (slightly higher than the average) and emits 9,217 pounds CO2 per year, which means switching from an Accord to a Prius would reduce CO2 emissions by 4,410 pounds. Therefore, we think this claim is wrong—one could eliminate all beef consumption and not come anywhere close to reducing the amount of CO2 that would be reduced by switching from a standard to an ultra-efficient vehicle.

Looking at the big picture, how much do we need to reduce our emissions? According to the UN and the World Bank, in 2006 the total US emissions per capita were approximately 42,460 pounds, of which "household" emissions (which includes vehicle emissions) were 20,680 pounds. US emissions were more than four times the global emissions per capita of 9,460 pounds. According to the 2007 report from the Intergovernmental Panel on Climate Change (IPCC), global CO2 emissions need to be reduced from the 2000 level by between 50% and 85% by 2050 in order to keep the average global temperature change at what is considered an acceptable level of between 2.0 and 2.4 degrees Celsius. This means the global per capita figure must fall to one eighth or less the US per capita figure. The US, a carbon intensive nation, would have to reduce its emissions by an astonishing 37,000 pounds or more to reach the global target, though no one expects nor is the US being asked to achieve that level of reduction.

Climate change can't be stopped by just changing our eating habits, by just changing our transportation habits, or by just changing any one other thing—we need to make meaningful changes across the board.
Claim #1: emissions from 2.2 # beef equivalent to 155 Mi Euro driving
Euro Mi155NYT
Beef #2.2NYT
Euro gr CO2 / km140.0Wiki
gr / #453.6Wiki
Mi / km0.621Google
Population 2009 (M)307Census
Beef M # 200926,800USDA
Avg Vehicle Mi / yr10,000
Avg MPG20
Avg CO2 / Vehicle / yr10,211US EPA 10,000 Mi 20 mpg
Avg CO2 / Vehicle / yr12,500US EPA
Euro Mi / Beef #70.5
Euro # CO2 / km0.309
Euro # CO2 / mi0.497
# CO2 / # Beef35.0
Beef / Capita 200987.3
# CO2 Beef / Capita 20093,055
CO2 Euro Vehicle / Beef6,150
US # CO2 / mi1.021
CO2 US Vehicle / Beef2,992
Claim #2: 20% beef reduction equivalent to switch from standard to ultra-efficient vehicles
Beef Reduction0.2
Accord (21 MPG) CO2 / yr9,217
Civic (25 MPG) CO2 / yr7,894
Prius (48 MPG) CO2 / yr4,807
Reduced # CO2 at 20% less beef611
# CO2 Accord - Prius4410
# CO2 Civic - Prius3087

- Stuart M. Whitaker

Sunday, August 7, 2011

Transportation Requirements: Reliability

One requirement of any transportation system is that it be reliable--absent reliability, people on inflexible schedules who have a choice of transportation mode won't choose public transit. In order to test the reliability of public transit in northern Virginia, we used an Apple iPhone with GPS enabled to capture (see photos below) the arrival times on four randomly selected stops served by the Fairfax Connector.

How reliable is public transport in Northern Virginia? In our sample, the best arrival was one minute late, the worst was 11 minutes late, with a seven minute average. When routing passengers with connections, the local transit Route Planner builds in five minutes between arrival of one segment and departure of the next segment, which means with this seven minute average delay, most connections would be missed. While this sample size is too small to give any confidence in the level of system reliability, a seven minute delay is a cautionary indicator that calls for closer examination.

Date.time (yymmdd.hhmm)LatLongStopScheduledRouteLate?
110805.113338.9165, -77.220667Tysons Corner Shopping Center11:32FC4021
38.895667, -77.225
Gallows Rd & Elm Pl20:54FC4018
38.916333, -77.221333
Tysons Corner Shopping Center20:59FC4018
110806.223338.914333, -77.221667Tysons Corner Shopping Center20:22FC40211

- Stuart M. Whitaker