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It's winter, 2018, in Iowa, five months after the last of the nuclear bombs detonated across megacities in northeast Asia, from Seoul to Tokyo to Shanghai. Radioactive fallout was the initial concern, but now something else is going awry: the weather.

American farmers accustomedto snow and cold during the winter would be forgiven for mistaking their corn and wheat fields for the Arctic tundra, as temperatures dip well below zero at night, and barely recover above 10 degrees Fahrenheit during the day, under a milky, leaden sky.

Forecasters say the corn and wheat harvest may be significantly shortened this year, and for the next several years. In fact, fears of a famine on an international scale are settling in.

This is what our world could look like just a few months to years after a regional nuclear war breaks out on the Korean Peninsula and spreads to include China and possibly Russia.

Whether from a deliberate strategy or a terrifying miscalculation, such a war could trigger a global climate catastrophe, experts warn, that is not being factored into leaders' planning.

Such a war could cause the planet to cool by up to 10 degrees Celsius, or 18 degrees Fahrenheit, with larger regional swings and extremes, according to Owen Brian Toon, a scientist at the University of Colorado at Boulder. The amount of cooling could be far lower, depending on whether the conflict were more limited in scope.

Apocalyptic visions of a so-called global “nuclear winter” were popular during the Cold War when envisioning a U.S. conflict with the then-Soviet Union, but the odds of a regional nuclear war in recent times have jumped higher after President Donald Trump’s bellicose rhetoric toward North Korea on Tuesday.

Trump's words, threatening to meet North Korea's threats with a "fire and fury like the world has never seen" were the starkest warning of a nuclear strike from any U.S. president in modern times.

It's not just national security experts who are horrified by Trump's words. Trump's rhetoric, and history of openly considering using nuclear weapons, is also concerning to climate scientists.

Two researchers, in particular, are taking note of the North Korean threat: Alan Robock, of Rutgers University, and Toon. Robock and Toon are modern day Cassandras, having warned for decades about the potentially ruinous climate change consequences of a nuclear war, most recently focusing on regional conflicts.

Robock has conducted much of the research into the idea of a nuclear winter, whereby a global thermonuclear war vaults so much smoke into the upper atmosphere to block out the sun for years afterwards, causing temperatures to plunge and killing off vital crops and plant and animal species.

Unlike the character from Greek mythology, they don't make prophesies so much as publishing peer-reviewed scientific studies. But, like the mythical character, few have paid attention to their warnings.

Right now, both Robock and Toon are focused on the mounting tensions on the Korean Peninsula, where a nuclear-armed dictatorship threatens to strike the U.S. or its allies, potentially igniting a regional nuclear war.

Robock says most people, including high-ranking defense officials, are unaware that a nuclear war occurring halfway around the world from the U.S. could seriously harm the homeland, by altering the climate.

A new little ice age

Simulations in the 1980s, he said, found that temperatures would plunge so far after a U.S.-Soviet nuclear war that high temperatures in the summer temperatures would stay below freezing worldwide.

The modern-day nuclear scenario that Robock, Toon and others have studied closely involves an exchange of nuclear weapons between India and Pakistan, with about 50 bombs of 15 kilotons each, which is less than half of those nations' nuclear arsenals.

A 2007 study published in the journal Atmospheric Chemistry and Physics found that, if these weapons were aimed at the center of large cities, the direct fatalities would be "comparable to all of those worldwide in World War II."

Such a war would induce massive firestorms in urban areas that could send up to 5 million tons of smoke high into the upper atmosphere, where tiny particles known as aerosols would scatter sunlight, preventing it from reaching the Earth's surface.

This would turn the planet's climate sharply colder, despite the effects of human-caused global warming, and impact areas far from the actual fighting. The global cooling from such a regional war could be near 1.25 degrees Celsius, or 2.25 degrees Fahrenheit, studies have shown.

Once in the stratosphere, the particles contributed by the smoke would stick around for a long time, Toon and Robock's simulations show. Observations after volcanic eruptions and wildfires support the model simulations.

“It circles the globe and stays there for many years," Toon said.

Toon cites firestorms during World War II in Hiroshima and Dresden, Germany, as real-world examples of what computer model simulations show could occur from a nuclear war taking place in an urban setting.

And it's not just one computer model simulation that is projecting a sharp global cool down and potential famine from a nuclear conflict, Toon says. “This is something that has been confirmed now in multiple climate models,” Toon said, citing both U.S. and European modeling studies.

In an interview, Robock warned that a nuclear war on other side of the Earth, “using much less than one percent of the current nuclear arsenal,” or just .03 percent of the explosive power of all the world's nuclear weapons in existence, could produce “a larger climate change than ever recorded before in human history.”

Not just a regional issue

Toon also said the central lesson of much of the research into how the climate would respond to a limited nuclear war is not at all comforting.

“It really suggests that it would be damaging for the world's climate to have even a small nuclear war, to the extent that even if a major power like the US were to launch a nuclear attack against another country,” then the damage to agriculture and ecosystems could “potentially lead to a nuclear famine.”

“It would be suicidal," he said of using even a limited number of nuclear weapons.

Robock said that an India-Pakistan nuclear scenario would cause such severe climate change worldwide that agriculture in the main growing regions of the U.S. and China would be reduced for more than a decade afterwards. These two areas supply most of the grain that feeds the world, and slashed production could lead to widespread famine.

“That’s our shocking result that we’ve gotten so far,” Robock said of his research.

A war between North Korea and the U.S. would likely involve fewer nuclear weapons than India versus Pakistan, which could limit the global environmental impacts. However, if it draws in China and Russia, which both border North Korea, then all bets are off, Robock says.

North Korea is thought to have anywhere between 10 and 60 nuclear weapons, not all of which are operational.

However, once started, nuclear wars can spiral out of control. “Another issue is once a nuclear war would start it’s really hard to control it,” Robock said, noting that China could be drawn in quickly.

“So the scenario could get really horrible.”

"If they used 10 weapons instead of 100 you might get one-tenth of the [climate change] response" when compared to India and Pakistan, Robock said.

Reached by email on Wednesday, Robock pointed to a statement from the International Physicians for the Prevention of Nuclear War, which calls for the de-escalation of threats between the U.S. and North Korea, and the abolishment of these weapons.

I can't hear you...

One might think that the climate change implications of a nuclear war would generate interest from government agencies that are involved in building, maintaining, and delivering such weapons, as well as deciding when and where to launch them. However, Robock and Toon both say they've been rebuffed from the Energy Department, Defense Department, and the Department of Homeland Security.

“No one wants to stick their neck out to fund our research,” Robock said.

“I’m concerned and I’m surprised by the lack of common understanding of our research,” Toon said. “It is alarming that there are people who don’t know this who are in charge of our nuclear arsenal.”

Robock is a passionate advocate for doing away with nuclear weapons but says the U.S. has taken the position that this is an unrealistic goal right now, while working to contain nascent nuclear powers like North Korea and Iran.

The United Nations is pursuing a treaty on the abolishment of nuclear weapons, but the U.S. and other nuclear powers are abstaining from the process, even going so far as to denounce it as unrealistic.

Instead of relying on government funding, Toon and Robock are pursuing their work with the help of a recent $3 million grant from the Open Philanthropy Project, which is run in part by Dustin Moskovitz, a Facebook co-founder.

Using the new funding, they hope to fine-tune computer models to provide more precise guidance to policy makers and the public about the climate consequences of various nuclear war scenarios.

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