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A nuclear winter is a theoretical concept, but if the climate scenario expected to follow a large-scale nuclear war, in which smoke and soot from firestorms block sunlight, came to fruition, global temperatures would sharply drop, extinguishing most agriculture. A nuclear winter could last for more than a decade, potentially leading to widespread famine for those who survive the devastation of the bomb blasts.

Now, a team led by researchers at Penn State have modeled precisely how various nuclear winter scenarios could impact global production of corn—the most widely planted grain crop in the world. They also recommended preparing "agricultural resilience kits" with seeds for faster-growing varieties better adapted to colder temperatures that could potentially help offset the impact of nuclear winter, as well as natural disasters like volcanic eruptions.

In findings recently published in the team reported that the level of corn crop decline would vary, depending on the scale of the conflict.

A regional nuclear war, which would send about 5.5 million metric tons of soot into the atmosphere, could reduce world-wide annual corn production by 7%. A large-scale global war, injecting 165 million metric tons of soot into the atmosphere, could lead to an 80% drop in annual corn yields. In all, the study simulated six nuclear war scenarios with varying soot injections.

Because of the crop's global significance, the researchers chose to model corn's collapse in a nuclear winter to represent the expected fate of agriculture overall, according to study first author Yuning Shi, associate research professor in Penn State's Department of Plant Science. He noted that an 80% drop in global crop production would have catastrophic consequences, leading to a widespread global food crisis. Even a 7% drop in global crop production would have a severe impact on the global food system and economy, likely resulting in increased food insecurity and hunger.

The simulations were possible thanks to the Cycles agroecosystem model, created a few years ago by scientists in Penn State's College of Agricultural Sciences, including lead developer Armen Kemanian, professor of production systems and modeling and corresponding author on this study.

Using high-performance computing and considering atmospheric conditions, Cycles enables large-scale, high-resolution, multi-year simulations of crop growth by meticulously tracking the carbon and nitrogen cycles within the soil-plant-atmosphere system.

"We simulated corn production in 38,572 locations under the six nuclear war scenarios of increasing severity—with soot injections ranging from 5 million to 165 million metric tons," Shi said. "This investigation advances our understanding of global agricultural resilience and adaptation in response to catastrophic climatic disruptions."

In addition to considering the effects of massive amounts of soot in the atmosphere, the researchers modeled the increase in UV-B radiation—a type of ultraviolet radiation that can lead to DNA damage, oxidative stress and reduced photosynthesis in plants—that would reach Earth's surface in a nuclear winter that could further limit agriculture.

Shi said he believes that this was the first study to estimate the extent of UV-B radiation damage to agriculture after nuclear explosions, which the researchers predicted would peak six to eight years after a global war. They estimated this could further cut corn production by an additional 7%, for a total worst-case scenario of an 87% drop in corn production.

Ozone high in Earth's atmosphere effectively absorbs the bulk of UV radiation the planet receives from the sun, but nuclear war would dismantle this ability, Shi explained.

"The blast and fireball of atomic explosions produce nitrogen oxides in the stratosphere," he said. "The presence of both nitrogen oxides and heating from absorptive soot could rapidly destroy ozone, increasing UV-B radiation levels at Earth's surface. This would damage plant tissue and further limit global food production."

While the predictions point to potentially catastrophic drops in the production of corn varieties currently grown, Shi said, switching to crop varieties that can grow under cooler conditions in shorter growing seasons could boost global crop production by 10% compared to no adaptation. However, seed availability for these crops could become a serious problem—a "bottleneck to adaptation," the researchers said.

Their proposed solution is to prepare "agricultural resilience kits" ahead of any nuclear disaster, containing region- and climate-specific seeds for crop varieties that can grow under cooler conditions with shorter growing seasons to survive lower temperatures.

"These kits would help sustain food production during the unstable years following a nuclear war, while supply chains and infrastructure recover," Kemanian said. "The agricultural resilience kits concept can be expanded to other disasters—when catastrophes of these magnitude strike, resilience is of the essence."

Shi noted that while proactive, internationally coordinated planning for such kits is unlikely, simply increasing awareness could help lead to better preparedness. "If we want to survive, we must be prepared, even for unthinkable consequences," he said.

Kemanian said he sees value in the research beyond human-caused calamity.

"Recall that catastrophes of this nature can happen not just because of nuclear war, but due to, for example, violent volcanic eruptions," he said.

"One may think that studies of this nature are just navel gazing, but they force us to realize the fragility of the biosphere—the totality of all living things and how they interact with one another and the environment."