Quick Answer — Shipping Mode Matters More Than Distance
"Food miles" is a popular but often misleading shorthand — what actually determines transport emissions is the shipping mode, not just the distance traveled. This calculator uses representative emissions factors in grams of CO2 per tonne-kilometer: ocean freight is by far the most efficient at roughly 20 g/tonne-km, rail freight around 35 g/tonne-km, truck freight around 110 g/tonne-km, and air freight around 1,130 g/tonne-km — more than 50 times higher than sea shipping per unit of weight and distance.
This means a food item shipped a very long distance by sea can have a smaller transport footprint than the same item trucked a much shorter distance, and air-freighted produce (common for items that spoil quickly, like berries or fresh fish) carries an outsized emissions cost regardless of the actual mileage.