Reducing animal product consumption may be a fairly direct route to reducing one’s greenhouse gas footprint and offers collateral health and environmental benefits. Eating locally grown food may additionally save a modest amount of greenhouse gas emissions, by eliminating long distance transportation.
Overall, it appears that agriculture accounts for a little under 10% of greenhouse gas emissions (GHG’s) in the United States. Animal products account for a disportionate share — perhaps as much as 2/3, in other words for more climate change than all of the carbon dioxide from home heating in the United States, which only accounts for 6% of carbon dioxide production in the United States.
Two professors at the University of Chicago recently sought to answer the question of how much carbon a vegan diet could save. Their paper does a sophisticated analysis and concludes that, for an individual American, the average American diet — including, fish, meat, poultry and diary in average quantities — results in about 1.5 more tons of carbon dioxide equivalent emissions per year than an entirely vegan diet.
1.5 tons of carbon dioxide per year is roughly the amount saved by trading in a car that averages 25 miles per gallon and buying a car that averages 38 miles per gallon (if one drives 12,000 miles per year).
For a family of four, of course, the decision to choose a fully vegan diet would save proportionally more — roughly 6 tons (4 x 1.5) — an amount likely to approach the entire carbon cost of heating their home in the Northeast (consistent with national figures) and with the post on personal carbon budgeting.
The sophisticated Chicago analysis aggregates upwards from data about the carbon footprint of individual food categories. One gains some comfort about that complex analysis by working downwards from the macro quantities developed on the total carbon emissions of the livestock sector of American agriculture. If one just divides the estimated livestock related emissions by the U.S. population, one gets 1.2 to 1.5 tons per person. Translating this total into an estimate of the consequences of eating animal products requires adjusting for (a) the export shares of animal (under 10%) and non-animal (roughly 25%) of agricultural products exported; (b) the necessary increased consumption of non-animal foods (to make up from the roughly 25% of total dietary caloriescurrently consumed as animal products). These adjustments result in an estimate of 1.1 to 1.3 tons of carbon dioxide savings for an average American converting to a vegan diet — just a little below the Chicago estimates.
The carbon dioxide consequences of dietary change are hard to estimate with precision, but we can have some confidence that they are in the ball park suggested above. The Chicago study finds (at page 9) that even though some plant food diets are more efficient than others, these differences are much smaller than the differences between plant foods and animal foods.
Of course, there is no need to make “all or nothing” choices or sudden changes in diet — incremental reductions in animal product consumption have proportionate incremental benefits.
One way to approach the choice is to reduce consumption of animal products while favoring local livestock producers that use sustainable and humane production approaches — often more costly than conventional approaches.
There many good reasons to purchase products from trusted local farmers — loyalty to start and another reason being that one can more readily confirm the quality of their food and their adherence to sustainable agriculture practices.
However, savings of greenhouse gases associated with transportation are likely to be only a modest additional reason to buy locally. First, transportation carbon costs appear to be a relatively small portion of total food carbon costs. Second, long haul bulk transportation is quite efficient. A fully loaded trailer truck travelling straight from California to an East Coast produce market, although it travels much further, may burn relatively little fuel per pound per mile as compared to local lorries travelling partially loaded among farmers markets; and rail transportation is an order of magnitude even more efficient (compare freight ton-mile statistics by mode with fuel consumption statistics by mode). Third, the personal market-to-home costs of shopping in a multitude of locations are considerable if one drives rather than walking or cycling — over all, food shopping trips may account for almost 29% of carbon consumption associated with food transportation, according to the Michigan study of the food sector (see Appendix B and figure 5). For another, well-balanced, discussion of transportation issues in food see the National Sustainable Agriculture Information Service.