Heat and eat
The climate impact of food
The food system is responsible for up to one-third of global greenhouse gas emissions.
It won’t show up on a supermarket docket, but the production, transport, packaging, refrigeration and distribution of food all add to the climate bill before it even makes it to our mouths.
Some foods are much more emissions-intensive to produce than others, though, and that can change depending on where in the world you live and the production techniques used.
Research devoted to working out the ‘cradle-to-grave’ emissions cost of all sorts of different foods is growing every day. Here in Aotearoa, researchers at Otago University published a New Zealand-specific food emissions database in 2020, that shows the huge differences between certain groups of food, and even items within those groups.
There are about 350 food items in the full database — we’ve shown 83 of them here.
To make this chart more readable, we’ve used something called a log scale. The numbers up the side of the chart aren’t evenly spaced, which helps to show a wide range of values in a small space.
This can magnify small differences though, and make large differences seem smaller.
So here’s how the same data looks on a regular scale. You can see the real gap between some meat and dairy products, and the rest of the groups.
Even with a log scale, though, some foods stand out.
While the differences in individual items are interesting, Otago University associate professor of public health and senior study author Alex Macmillan says what’s most important is “the huge order of magnitude of difference between plant-based foods and meat, particularly red meat”.
Beef meat gets one of the highest scores because of the time and food it takes to get a beast to slaughter-weight.
Industrially-produced crustaceans like crayfish (rock lobster) and crabs also emit an enormous amount of greenhouse gases, kilogram for kilogram.
But traditionally gathered kōura and other kaimoana may have a much lower impact because ‘production’ is low-intensity, Macmillan says. “We don’t have the life-cycle assessments for that … but it’s likely to be incredibly sustainable.”
Likewise, there isn’t data for everything Kiwis eat — and some of the other items missing may have lower emissions, and offer possible dietary alternatives.
The Otago researchers found the transport costs associated with almost all foods made up a small fraction of overall emissions. “We get these messages all the time that we should eat local and the air miles are really important,” Macmillan says. “[But] what you eat matters much more than where it comes from.”
Rice is a good example: yes, we import it, but most of the emissions come from rice paddies, which emit methane.
The level of processing also matters.
Similarly, dried fruit has a much higher value than any of the fresh fruit or vegetable items.
New Zealand is great at producing food, though. So what new things might we grow if we were serious about collectively shifting to a low-carbon diet?
Macmillan says we only need to look to the recent past, when parts of New Zealand grew much more grain. “We could be looking at the 20% of our food we import, because we know we can grow some of those here: wheat, rye, legumes.”
Changing your diet permanently takes time, effort — and sometimes money.
Macmillan says the focus should be on system-level change, rather than individual choice, to ensure everyone can access a sustainable diet.
That could include making certain foods cheaper by removing GST, using institutions like schools and hospitals to introduce people to alternatives, and diversifying or changing the types of foods we produce.
Explore the data yourself.
To compare foods that make mainly methane with foods making carbon dioxide, we’ve used the global warming potential (over 100 years) per kilo of product. This is the standard typically used when countries submit their climate footprints to the UN.
Some researchers and producers argue this unfairly inflates emissions for foods that create a lot of methane, which produces a lot of heat in the short-term but doesn’t linger in the atmosphere. They advocate for a different way of comparing emissions, which weights emissions based on the additional warming they cause, rather than the total warming. This lowers the long-term footprint for red meat and other high-methane-emitting foods.
Other researchers say we should use a different method again, focusing more on the near-term warming potential. This results in even higher footprints for methane-heavy foods.
In the absence of global agreement on the best way to aggregate emissions, we’ve stuck with the current standard.
It’s worth noting that red meat still typically makes a bigger contribution to global warming than most other foods, regardless of which system you use. This also holds true if you calculate emissions per serving size (which are typically smaller for protein-rich foods).
New Zealand products can be relatively lower in emissions than elsewhere, although it varies from farm to farm. Some values in the Otago data are based on New Zealand research, while others are modified for a New Zealand context from overseas studies. New life-cycle assessments are gradually being produced in New Zealand, that may result in different values to those included in this database.