People often think that eating ‘local’ – buying foods which are produced close to home – is one of the most effective ways to reduce our carbon footprint.
This is certainly true for foods that are transported by plane. But the reality is that very little of our food is.
One simple way to compare the means of transport for food is to sum up how many kilometers planes with food freight travel; and compare this to how how many kilometers trains, and ships, and trucks do.
But this does not give the complete picture because a boat can carry much more food for a given distance than a truck can. To give an informative comparison, we use a metric called ‘food miles’; this is calculated as the distance each transport method covers multiplied by the quantity of food transported (by mass). This gives us a comparison of food miles in tonne-kilometers.
The chart here shows the share of global ‘food miles’ by transport method. This data is sourced from the work of Joseph Poore and Thomas Nemecek, published in the journal Science in 2018.1
As the data here shows, only 0.16% of food miles come from air travel. Most – nearly 60% – comes by boat.
You can see this data in absolute terms, in tonne-kilometers, here.
Transporting food by air emits around 50 times as much greenhouse gases as transporting the same amount by sea. More specifically, 0.023 kilograms of carbon dioxide-equivalents (CO2eq) per tonne-kilometer by sea, versus 1.13 kilograms CO2eq by air. We see these emission factors for different transport modes in the table.
For food that is transported by sea, transportation doesn’t actually add much to the carbon footprint. Since most of our food is transported by sea, transport emissions only account for 6% of the carbon footprint of food, on average.2
But for those food items that travel by air, travel distance does have a large impact. We should avoid air-freighted goods where we can.
Emission factors for freight by transport mode (kilograms of CO2eq per tonne-kilometer)3
|Transport mode||Ambient transport (kg CO2eq per tonne-kilometer)||Temperature-controlled transport (kg CO2eq per tonne-kilometer)|
|Road Transport||0.2||0.2 to 0.66|
|Sea / Inland Water Transport||0.01||0.02|
Which foods are air-freighted? How do we know which products to avoid?
Foods which are air-freighted tend to be those which are highly perishable. This means they need to be eaten soon after they’ve been harvested. In this case, transport by boat is too slow, leaving air travel as the only feasible option.
Some fruit and vegetables tend to fall into this category. Asparagus, green beans and berries are common examples of air-freighted goods.
It is often hard for consumers to identify foods that have travelled by air, since they’re rarely labeled as such. This makes them hard to avoid. A general rule is to avoid foods that have a very short shelf-life and have traveled a long way (many labels have the country of ‘origin’ which helps with this). This is especially true for foods where there is a strong emphasis on ‘freshness’: for these products, transport speed is a priority.