Scientists find the best crops to grow during the apocalypse

If a global catastrophe suddenly led to a nuclear winter, millions of people could starve. But now, scientists have figured out what crops we would need to grow to sustain a city if such a calamitous event occurred.

According to a new study, farming spinach, sugar beets, wheat and carrots in urban and near-urban areas could feed the population of a midsize city in a post-apocalyptic world.

The scientists built on previous research to determine the optimal crops to plant after a global catastrophe — such as nuclear war, extreme pandemics or solar storms. Their goal was to find the most efficient way to feed a person using the least amount of land.

"[The research] actually wasn't inspired by the current, you know, geopolitical environment," said study lead author Matt Boyd, founder and research director of Adapt Research, an independent research organization. "But it has turned out to be very relevant, obviously, to the current geopolitical environment," Boyd told Live Science.

Current events include unpredictable international politics, ongoing war in the Middle East and Europe, weaponized artificial intelligence and the ever-mounting destruction from climate change. In January, the Doomsday Clock, which indicates how close humanity is to a species-threatening disaster, ticked one second closer to midnight — the closest it has ever been to catastrophe.

In the new study, published Wednesday (May 7) in the journal PLOS One, the researchers looked at how the population of a midsize city could survive with agriculture in the event of a global disaster. The study examined two scenarios should disaster strike: what to grow in and around a city under normal climate conditions, and what to grow in the event of a nuclear winter.

The optimal crop to grow in a temperate city in normal conditions turned out to be a humble legume: peas. "Peas are a high protein food. They grow well in urban agriculture environments," Boyd said. "If you want to feed someone, growing peas minimizes the amount of land you need to feed that person."

However, pea plants are not frost-resistant. In the event of a nuclear winter — which could be caused by nuclear war, a supervolcano eruption or a huge asteroid strike — sunlight would be blocked "due to all the soot and everything that's been thrown up into the stratosphere," Boyd said. This in turn would lead to lower temperatures and make it harder for plants to photosynthesise.

In that scenario, a hardier combination of spinach and sugar beets are a better choice, the researchers found.

Related: 'Nuclear winter' from a US-Russia conflict would wipe out 63% of the world's population

Boyd and study co-author Nick Wilson, a professor of public health at the University of Otago, Wellington came to these conclusions in part by using the data from a meta-analysis of urban agriculture research that analyzed the yield of different crops in dozens of cities around the world.

Peas, for example, rose to the top in normal conditions because they require 3,143 square feet (292 square meters) of land to satisfy one person's caloric and protein needs for a year, whereas a combination of cabbage and carrots required 8,364 square feet (777 square meters), said Boyd — almost three times as much land.

The researchers chose Palmerston North in New Zealand, but the findings can apply to similar cities worldwide, the researchers said. With a population of roughly 90,000, it's a globally midsize city, Boyd said, plus "it's inland, like many cities around the world, and it has reasonably low density, suburban type housing, not sort of Manhattan-style skyscrapers and so forth."

The scientists then used Google imagery of Palmerston North to work out the total amount of available green spaces that could be used to grow crops, such as front lawns, backyards and parks.

"Surprise, surprise. The city can't feed all its people," Boyd said. If food is only grown within the city bounds, the available land can feed about 20% of the population with crops that maximize protein and food energy per square foot under normal climate conditions. That number shrinks to about 16% during nuclear winter.

To feed the rest of the population, people would need land immediately outside the city — about one-third of the size of the city's built urban area — to sow additional efficient crops. In the case of Palmerston North, that's about 2,817 acres (1,140 hectares), plus another 272 acres (110 hectares) of canola to convert into biodiesel to fuel tractors and other farm machinery.

In the land just outside the city, the study found that potatoes are ideal for a normal climate scenario, and a combination of 97% wheat and 3% carrots is the optimal ratio during a nuclear winter because they have a higher tolerance for colder temperatures.

Even in cities, "there is a ton of farmland that can be used to grow food," said Theresa Nogeire-McRae, a landscape ecologist at American Farmland Trust and affiliate faculty at Oregon State University, who was not involved in the study.

“People settled cities where they did for a good reason,” Nogeire-McRae told Live Science. “It was the rich soil near riverbanks. It's a good commodity. Let's not throw that away." She added that the methods of study were sound and the findings were reasonable.

Boyd noted there are a number of unknowns that would impact crop yield in the real world. Soil quality is a big variable, because lower quality soil would yield fewer crops. He also assumed a scenario where water systems were still flowing — "but you can imagine global catastrophe scenarios where there's additional obstacles and problems," he said. He also doesn't expect people will only eat peas for an entire year, but planting the most efficient crops minimizes the amount of land needed to feed a population.

Boyd said this study could be used as a first step for cities looking to use resilient urban agriculture in land use policy.

"Decisions that might seem optimal in one lens, maybe economically, may look a little bit less optimal if you were also including a lens like resilience, safety and well-being," he said.