What food miles measure and what they miss

The idea of food miles came from Tim Lang, a British food policy researcher, and the SAFE Alliance, a coalition of farming and environmental groups. It first appeared in print in 1994 in The Food Miles Report by Angela Paxton, which set out the costs of hauling food over long distances. The term was built to be simple: a number that anyone could picture and that pointed at a real change in how food reached shops, with fewer, larger suppliers and more trucks on the road.

It worked as a slogan. As a measurement it has two problems. Distance says nothing about how the food moved, and transport is only one stage in a food’s life, often a small one.

How it moves matters more than how far

A ton of apples on a container ship and a ton of apples in the hold of a plane can cover the same distance with very different results. In 2005 a study commissioned by the British environment department looked at every leg of the country’s food transport and found air freight carried about 1 percent of the tonne-kilometers but produced about 11 percent of the carbon dioxide. Its authors concluded that a single indicator based on distance would not be a valid measure of sustainability and proposed several narrower ones in its place, including one for air freight and one for the shopper’s car.

That second one is easy to forget. The trip from the supermarket to the kitchen counts, and in the British data cars made up nearly half of the vehicle kilometers driven for food. A separate drive to a farm stand for one carton of eggs spreads a whole car trip over a dozen eggs. A delivery truck spreads its trip over thousands.

Production usually outweighs the trip

A widely cited American study, published in 2008 by Christopher Weber and H. Scott Matthews of Carnegie Mellon University, added up the greenhouse gases behind what the average U.S. household eats. The total came to about 8.1 metric tons of carbon dioxide equivalent a year. Production accounted for 83 percent of it. Transport across the whole supply chain accounted for 11 percent, and the final delivery from producer to store for only 4 percent.

The spread between foods was far larger than the spread between near and far. Red meat was on average around 150 percent more greenhouse-gas intensive than chicken or fish. The authors worked out that moving less than one day a week of calories from red meat and dairy to chicken, fish, eggs or vegetables would cut more emissions than buying every item locally.

That finding is why food miles alone can mislead. A locally raised steak starts far behind an imported bag of lentils, and no amount of short hauling closes that gap.

Where distance does count

A later study pushed the other way. In 2022 a team led by Mengyu Li at the University of Sydney published a global model in Nature Food that traced transport through the entire upstream supply chain across 74 countries. It put food transport at about 3 gigatons of emissions a year, roughly 19 percent of food-system emissions, several times higher than earlier estimates.

The two figures come from different models with different scopes, one built around American households and one around the global economy, so they are not a straight contradiction. The newer one counts more of the hauling that happens before a food is finished.

The 2022 study found where distance counts most. Vegetables and fruit made up more than a third of food transport emissions, and for them transport produced nearly twice the emissions of growing them, largely because so much produce travels chilled. Wealthy countries, with about 12.5 percent of the world’s people, generated about 46 percent of the emissions from international food transport. The authors’ advice was a shift toward plant foods combined with more local sourcing in affluent countries.

Read together, the studies point one way for meat and dairy and another for fresh produce. For a steak, where it was raised matters less than whether it is on the plate at all. For a clamshell of berries in January, the trip may be the largest part of its footprint.

What else the number leaves out

Season changes the answer. In the British study, tomatoes trucked from Spain could take less energy than tomatoes grown out of season in heated glasshouses at home. The same crop from the same place scores differently in July and in February.

Storage adds its own cost. Apples and potatoes eaten months after harvest have often spent that time in cold storage, which draws power every day it holds the crop.

Waste is left out entirely. Food that spoils before it is eaten carries its whole production footprint into the bin. Short, fast supply chains help with fragile produce; for grains and dry goods they make little difference.

Then there is everything that isn’t carbon. Food miles began as a way to point at the social and economic costs of long supply chains as well as the environmental ones. The 2005 British work put the wider cost of food transport at more than £9 billion a year, most of it in congestion.

Using it anyway

Food miles remain a reasonable first question for fresh produce. The likeliest candidates for a long, chilled or airborne trip are fragile fruit and vegetables sold far from their season, and choosing what is in season nearby avoids much of that. For the rest of the basket, the bigger lever is what goes in it rather than how far it came. And the last mile is the shopper’s own: one planned trip for the week does more than a detour to the farm stand for a single item.