You can reduce your carbon footprint by not only paying attention to what you eat - but where it comes from.
A study published in Nature Food has found that 6 per cent of global greenhouse gas emissions are related to food transport. This number is an order of magnitude higher than some previous estimates.
"Our study estimates global food systems, due to transport, production and land use change, contribute about 30 per cent of total human-produced greenhouse gas emissions," says lead author Dr Mengyu Li, a researcher at the University of Sydney's School of Physics.
"So, food transport - at around 6 per cent - is a sizeable proportion of overall emissions. Food transport emissions add up to nearly half of direct emissions from road vehicles."
The researchers used economic data from 74 countries, 37 sectors (including things like fruit and vegetables, coal, livestock and manufacturing), and four transport methods, to model food production journeys around the world.
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"One of the powerful things about our calculation is that it enables the consumer to know the full cost of the food that they're eating, in terms of emissions," says co-author Professor David Raubenheimer, a researcher in nutritional ecology, also at the University of Sydney.
"Whereas previously, almost all of the calculations took into account just the actual transport of the food itself, we've taken into account the transport of the food, as well as all the things that need to be transported in order to produce that food - like chemicals and machinery."
This has led to an emissions estimate from food transport up to seven times higher than previous estimates. Globally, according to their analysis, food transport accounts for three billion tonnes of CO2-equivalent emissions every year. (For context, Australia emits roughly 500 million tonnes of CO2-equivalent each year.) This represents 19 per cent of total food-related emissions, and 6 per cent of total global emissions.
The emissions impact was not uniform. Unsurprisingly, countries with large populations - China, the United States, India, and Russia - were the largest food transport-related emitters.
But per capita, richer countries were responsible for far more food transport emissions than poorer countries. Up to 46 per cent of the total food transport emissions came from countries that represented 12.5 per cent of the world population.
Food transport emissions add up to nearly half of direct emissions from road vehicles.- Dr Mengyu Li, University of Sydney
"A lot of this is driven by consumers becoming spoilt and expecting aseasonal food," says Raubenheimer.
Australia, as a large exporter of food, was the second-highest exporter of food-transport related emissions. But Raubenheimer points out that, because of Australia's size, eating domestically grown food can still carry a large emissions impact.
"One of our findings actually was that per kilometre, land transport is much more intensive than international transport because shipping is more efficient than rail or road," he says.
Type of food also influences transport emissions. Li says since vegetables and fruit require temperature-controlled transportation, their food miles emissions are higher. So, eating Queensland-grown fruit in Perth is not eating locally.
"That will be very expensive food in terms of emissions, because of the high cost of land transport," says Raubenheimer. "The more local, the better."
In fact, the researchers found that in a hypothetical scenario where everyone ate very localised food, total global transport emissions were 380 million tonnes of CO2-equivalent: just over a tenth of their current value.
It's unlikely to be possible to get emissions that low, because some countries need to import food to sustain their populations' nutrition.
Nevertheless, the researchers hope that their findings motivate consumers to eat more locally grown food.
"Consumers need to look at it, that's important, governments need to look at it, and the other thing is a very positive trend towards ethical business and ethical investment. This is very powerful information for that," says Raubenheimer.
"For the history of our species, we've eaten locally what's available seasonally, and we really need to get back into that habit."
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