Where does food carbon footprint come from?

Food is a necessary part of our life, but have you ever questioned how much your diet impacts the environment?

As in most topics regarding sustainability, the answer is not clear-cut, although many quantitative studies are being conducted lately. To give a definition, a carbon footprint is calculated as the sum of the emissions resulting from every stage of a product’s lifetime, mainly greenhouse gases such as carbon dioxide, methane and nitrous dioxide. It is estimated that food accounts for 10-30% of a household’s carbon footprint.

The most common belief is that the best way to reduce the environmental impact of food is buying locally produced products, so as to reduce the emissions related to its transportation. This would be a good solution if transportation was responsible for a large share of food’s total carbon footprint. Actually, it has been shown in an analysis published on Science that it is not during transport and packaging that food “emits” the most, but instead during production processes: the latter accounts for 68% of food emissions, while transport on average only for 5%.

Emissions differ for each type of food. As we can see in the following graph, the ones that produce most greenhouse gases per kilogram of product are animal proteins, especially meat, but also dairy products.

The reasons behind this are several: the change in land use in favor of pasture, the use of fertilizers – also manure – and the enteric fermentation in ruminants, which all cause large quantities of methane to be released. Among meats, beef is the most polluting, with 60 kg of GHG per kilogram, while poultry and pork stop at 6 and 7 kg respectively.

The discussion surrounding the carbon footprint of fish, instead, is more complicated. It was once considered more carbon friendly than many other animal proteins, but recent research published on Nature has highlighted the polluting role of bottom trawling, which consists in dragging heavy nets across the seabed to catch fish. The issue behind this is that seabed sediments act as carbon sinks, and with this kind of trawling, they are churned up and release CO2. Being it the most common method of fishing in the world, the paper estimates it is responsible for 2% of total global carbon dioxide emissions.

Therefore, when compared to grains and vegetables, the difference in carbon footprint becomes significant: most plant-based products emit as much as 10-50 times less than animal-based ones.

What could help us reduce the environmental impact of our meals? By a strictly environmental point of view, limiting and even cutting out all animal derivatives seems like the best choice, as showed by the numbers presented above. However, it is always fundamental to remember that becoming vegetarian or vegan is not a simple step and must be considered and planned carefully from a nutritional standpoint. Finally, another crucial piece of advice is: don’t trash your food! Even though it might seem trivial, 1.3 billion tons of food are wasted every year, causing an estimated 3.3 billion tons of GHG to be released in the atmosphere.

Sources: BBC, The Guardian, Center for sustainable systems of University of Michigan

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