This post is because of this report. It summarizes a study on on the environmental impacts of conversion of mangroves for agricultural uses - raising cattle and shrimp farms. It quotes ""On a personal scale, this means a typical steak and shrimp cocktail dinner produced through mangrove conversion would burden the atmosphere with 1,795 pounds of carbon dioxide," said J. Boone Kauffman, an ecologist at Oregon State University who led the study. ... This is approximately the same amount of greenhouse gases produced by driving a fuel-efficient automobile from Los Angeles to New York City." "
There is a neat paper co-authored by the late Dr. Lee Schipper, who made great contributions to transportation sustainability. And some of the most telling number from his study is the picture below
As someone whose single biggest impact comes from air travel, I felt better that the airline industry has made great strides in reducing the GHG intensity. If you read the paper, this is attributed to fuel economy, and regulatory changes and higher occupancy per flight. Also rail travel is getting better but in terms of the passenger miles traveled in the US it's absolute impacts are likely smaller relative to road and air travel.
Now, let us crunch some numbers to compare the effectiveness of reducing meat vis a vis reducing vehicle miles traveled from a greenhouse gas perspective. I am using the assumptions below for protein, which come from this study. Emissions per mile of auto use are based on EPA reported fuel economy (harmonic mean of 50% city and 50% highway miles)
A few additional assumptions about the base line relative to which some adjustments will be compared:
Daily protein requirement for adult: 60 grams (gm)/day
Baseline protein mix: 45 gm of beef protein + 15 gm of chicken/milk protein + 0 gm legumes
Average annual vehicle miles (U.S.) - 12000 miles/year
Automobile for the base case - Ford F150
Below is the effectiveness of four different adjustments relative to the baseline
Reducing beef protein intake by 10% is as effective as driving 5% less miles using a F150. Switching to a Camry is four times as effective as each of the other adjustments shown. It is for oneself to decide which of these adjustments is easier. Of course bigger adjustments, combining more than one type of adjustments or different baseline assumptions will all affect the calculations.
Bottomline: There are any number of calculators to estimate your energy, water, CO2 footprint etc. But I have not come across a calculator that combines our various activities and various types of burdens and gives information about the effectiveness (say, on a % emissions basis) of adjustments along different fronts (food, travel, housing, etc.) and in terms of changing the equipment (or capital stock) vs usage and let the consumer make better informed decisions.