If a global catastrophe disrupted international trade and fuel supplies, our survival might hinge on a stark but practical diet of peas, potatoes, sugar beet and spinach.
At least that’s according to a new study published in the journal PLOS One.
The study, led by Dr Matt Boyd of Adapt Research Ltd and Prof Nick Wilson of the University of Otago in New Zealand, looked at how cities might feed themselves if global food systems failed – in the wake of events like a nuclear war, extreme pandemic or massive solar storm.
These scenarios could cut off access to vital resources such as fuel and fertiliser, crippling industrial agriculture and long-distance transport.
Previous research has pointed to urban agriculture – such as rooftop gardens and community plots – as a way to boost local resilience. But Boyd and Wilson wanted to know how far this could really go.
Using satellite imagery, they analysed the food-growing potential of Palmerston North, a city in New Zealand’s temperate climate whose population size sits near the global median – not especially large or small – making it representative of many urban centres around the world.
They found that even if every suitable space in the city were turned into a garden, urban agriculture could only feed about one-fifth of the population.
To feed the entire city, at least 1,140 hectares of nearby farmland would also need to be converted to food production. An additional 110 hectares would be required to grow biofuel crops to power farm machinery in the absence of liquid fuels.
But perhaps the most striking part of the study is the diet it envisions.
“Each person needs a certain amount of protein and food energy to avoid starving,” Boyd told BBC Science Focus.
“Of the crops that we studied, peas required the least land area to provide the protein and food energy needs of one person, when grown using methods typical of within-city cultivation.”
But while peas would survive fine in a catastrophe where the climate remains similar to today’s, they wouldn’t tolerate the frosty conditions expected after a nuclear winter, he explained.
This scenario, caused by soot from large-scale nuclear explosions blocking sunlight and cooling the planet, would shorten growing seasons and lower average temperatures. In such a case, sugar beet and spinach take the lead: both are hardy, high in food energy, and able to grow in cold, low-light conditions.
Just outside the city, industrial farming methods could still be used – provided there's nearby land and minimal reliance on fuel. In normal climatic conditions, potatoes can feed people using minimal land.
“But they are sensitive to frost,” Boyd said. No good in a nuclear winter then.
“It turns out that optimal protein and food energy is achieved for wheat if you include 3 per cent carrots and 97 per cent wheat. Wheat and carrots are both frost-resistant, and also require less liquid fuel than potatoes, another consideration in a no-fuel scenario.”
This, thankfully, doesn’t mean we’d be stuck eating only these foods. The study presents the most efficient options for feeding the greatest number of people using the least land – a kind of worst-case scenario diet.
“In reality, a mix of crops would likely be grown,” Boyd said. “But when determining what to grow near cities, consideration should be given to high protein and high food energy per land area crops.”
The researchers said their methodology could help cities worldwide assess their food security and develop land use policies that boost resilience. However, cities surrounded by lots of water, or larger, more dense metropolises, may need to consider different approaches.
“There is an increasing risk of global catastrophe, given emerging biothreats, geopolitical threats, and advancing technologies,” Boyd warned. “I like to say that societies need to prepare for 'destruction, not just disruption' of key global infrastructure.
“The kind of lens we've applied in our research shows that there are quite local solutions that could help build resilience if local authorities were supportive of these approaches and took a proactive approach.”
About our expert
Matt Boyd founded Adapt Research in 2015, an organisation performing independent and bespoke research in collaboration with research assistants and subject matter experts. His work focuses on analysing and mitigating global catastrophic and existential risks, as well as on technology and public health. Boyd's research has been published in peer-reviewed journals, including The New Zealand Medical Journal and the Australian and New Zealand Journal of Public Health, among others.
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