New_Scientist_3_08_2019

24 | New Scientist | 3 August 2019

T

HE popular narrative

with food is simple:

“eating local” is one of the

best ways to shrink your carbon

footprint. This is because food

miles are a handy proxy for overall

sustainability, as transporting

harvests across the planet is a key

driver of carbon emissions. It is

a story that is as pervasive in the

foodie media as it is intuitively

plausible, but how reliable is it?

Well, it is indeed true that the

food sector uses a lot of energy,

contributing 20 to 30 per cent

of all greenhouse gases. But how

much of this is directly down to

moving food around the globe

from farm to fork? Perhaps less

than you might think.

In one of the most

comprehensive studies,

researchers at Carnegie Mellon

University in Pennsylvania report

this to be just 4 per cent (thus

making up as little as 0.8 per cent

of the average carbon footprint

of someone in the US). Echoing

other research from around the

world, which suggests transport

generates just 4 to 6 per cent of the

food system’s carbon footprint,

the study found that most

emissions were actually generated

from other aspects of food

production, such as agriculture,

processing and cooking.

To put this in context, the US

Department of Agriculture found

that household kitchen appliances

generated nearly seven times

as much carbon emissions as

food transport. This figure is

particularly pertinent considering

that typical estimates of the length

of US food supply chains aren’t

exactly insignificant, coming in

at about 2400 kilometres.

In fact, considering all aspects

of our food system – whether

farming, processing, packaging,

transport, retail, food services

and households – it was the end

consumer that used by far the

most energy. Transport? The least.

OK, so food miles may not be

the largest driver of our food

system’s carbon emissions, but

surely every little bit helps when

it comes to reducing our carbon

footprint? The tricky thing is

that cutting transport distance

by swapping to a more local

producer can often involve an

environmental trade-off as the

carbon emissions of agricultural

systems can vary wildly.

One UK government study

found that tomatoes trucked

hundreds of kilometres from

sunny Spain had a carbon footprint

that was less than a third that of

those grown in heated glasshouses

in the chilly UK. Conversely, it

found that the opposite was the

case for crops like potatoes, where

the carbon emissions of

production were similar, meaning

transport from further afield had a

greater overall impact. In contrast

to the simple “local = more eco-

friendly” narrative, the authors

therefore concluded that: “A single

indicator based on total food

kilometres travelled would not be

a valid indicator of sustainability.”

When it comes to our carbon

footprint, transport methods vary

enormously too. For example, as

air freighting produces more than

75 times more emissions than sea

freight, shipping food to the UK

all the way from South-East Asia

would involve far less carbon

than the same product popped

on a short flight from Italy. In this

context, a single shipping food

mile is the equivalent of almost

8 road food miles and over 75 air

food miles, making the concept

of distance as a direct indicator

of emissions highly problematic.

Finally, even within the same

transport method, the concept

of food miles can belie the true

complexity of calculating carbon

emissions, such as economies of

scale. In a study at the University

of Bath, UK, researchers aimed

to compare the emissions when

consumers bought fruit and

vegetables directly from local

farms or through an organic box

delivery scheme. The box scheme

involved a carbon-hungry system

of cold storage, packing and

transport to and from a regional

hub, on top of delivery to the

consumer’s door. Yet despite this,

the efficiencies of scale meant

total emissions were still lower

than if all these consumers made

individual car trips direct to the

farm of 6.7 kilometres or more.

So is eating local really a better

option? It depends. There are

many reasons why you might

be choosing to do so, aside from

environmental concerns. Indeed,

there are many other ways to

measure environmental impact

other than carbon emissions.

But when we look at the evidence,

only one thing is clear: food miles

alone really aren’t a good proxy for

sustainability. In fact, sometimes

they are incredibly misleading.

While we can’t discount them

entirely, we should view them

in the context of a suite of other

factors, recognising that they

often make up a tiny fraction

TOPAE/SHUTTERSTOCK of food’s carbon impact. ❚

This column appears

monthly. Up next week:

theoretical physicist Chanda

Prescod-Weinstein

“ Tomatoes trucked

from Spain to the UK

had lower emissions

than those grown in

heated glasshouses in

the chilly UK”

Are food miles important? Cutting the transport distance from

farm to fork seems a sensible and straightforward way to lower

carbon emissions. But it’s not that simple, writes James Wong

#FactsMatter

What I’m reading

A lot of claims on

Twitter purporting that

modern fruit varieties

are 100 times richer

in sugar than their

ancestors. Spoiler: this is

essentially biologically

(and thermodynamically)

impossible.

What I’m watching

The new season of

Stranger Things,

back to back.

What I’m working on

I am trying (rather

unsuccessfully) to sort

out my work-life balance,

mainly by tending

to my vast collection

of houseplants.

James’s week

James Wong is a botanist and

science writer, with a particular

interest in food crops,

conservation and the

environment. Trained at the

Royal Botanic Gardens, Kew, he

shares his tiny London flat with

more than 500 houseplants.

You can follow him on Twitter

and Instagram @botanygeek

Views Columnist