The local food movement, with the goal of consuming food produced and grown within a close geographic region, has been gaining traction in recent years as a way of eating fresh and high quality foods and reducing one’s environmental impact. However, public messaging about the outcomes of this movement is divided and often leads to confusion and misunderstanding among consumers. This short article will attempt to break down some of the nuances of how a food’s carbon footprint relates to the distance it travels from farm to plate (commonly referred to as food miles).

So, do food miles really matter? Yes and no. 

For most American diets, the carbon cost of transportation is slight compared to the carbon costs of production (running the tractors, producing chemical fertilizer, pumping irrigation…). Therefore, the most effective way for most Americans to reduce their diet’s carbon footprint is not by buying local, but rather eliminating or reducing their consumption of animal products.

the most effective way for most Americans to reduce their diet’s carbon footprint is not by buying local, but rather eliminating or reducing their consumption of animal products. 

Cartoon by Harvard staff member, Mitra Farmand. www.mitrafarmand.com.Cartoon by Harvard staff member, Mitra Farmand. www.mitrafarmand.com.

For a vegan, food miles contribute to a larger portion of their food’s carbon footprint. Plant-based foods have lower production footprints, so transportation is comparatively more significant. Even then, the raw mileage is hardly informative for determining carbon footprints; the mode of transportation is the key variable. Cargo ships are the most efficient, followed by trains, then trucks, and lastly planes. 

That means a product flown from Chicago to Boston has a significantly larger carbon footprint than one shipped 11,000 miles from Asia to California.

Although exact numbers vary across analyses, flying one ton of food is close to 70 times more carbon intensive than transporting that same weight via a large cargo ship (source). That means a product flown from Chicago to Boston has a significantly larger carbon footprint than one shipped 11,000 miles from Asia to California. As a result, locality is more important for perishable foods that are often flown like raw fish, asparagus, and berries. Foods such as tomatoes, bananas, pears, and apples can all be harvested before ripening, stored for long periods of time, then inoculated with ethylene gas (the naturally occurring hormone produced by fruits that causes the change in color and flavor profile associated with ripening) before entering a supermarket. In many cases, these shelf-stable foods have lower carbon footprints when produced internationally because the carbon cost of production far outweighs that of transportation.

Another frequently cited comparison is that of lamb produced in England verses lamb produced in New Zealand. For a consumer in England, the New Zealand lamb actually has a lower carbon footprint. Our intuition failed us. Why? Sheep in New Zealand are generally raised on farms run by hydroelectric power. This energy saving is so immense that it overrides the fuel output of the 11,000 mile cruise to England (source).

A similar story unfolds here in Boston. Local meat production could be more carbon intensive because the animals must be housed in heated facilities during the cold winter months. For a large portion of the year, we are better off shipping in a tomato from South America than growing one in a local greenhouse.   

A similar story unfolds here in Boston. Local meat production could be more carbon intensive because the animals must be housed in heated facilities during the cold winter months.   

Looking exclusively at carbon footprints neglects other important issues like water usage and farmer rights but it is none the less a valuable metric. Purchasing local food has many social benefits like boosting local economies, and increasing community cohesion and self-reliance. In conclusion, local food is not ‘good’ or ‘bad’, but it is important for consumers to define the values they hope to support through their purchasing decisions and think critically about when and where local foods support those values.     

Looking exclusively at carbon footprints neglects other important issues like water usage and farmer rights but it is none the less a valuable metric.