Red-hued image of a nuclear mushroom cloud
Nuclear winter would follow a prolonged series of nuclear explosions in urban areas. The more than 2,000 nuclear explosions that have already detonated have largely been in unpopulated areas, such as Bikini Atoll, above. Credit: U.S. Department of Energy

The thought of nuclear war may conjure images of looming mushroom clouds, duck and cover drills, or local radiation fallout. These immediate effects are terrifying, but scientists say the fallout of a nuclear war would likely last well beyond the initial explosions.

In a new paper in the Journal of Geophysical Research: Atmospheres, researchers detail a decade of destruction following a nuclear war between the United States and Russia. Smoke from smoldering cities is projected to make its way to the stratosphere, where it will trigger a nuclear winter.

The team used new climate models to approximate just how long—and how severe—the nuclear winter might be if Russia and the United States engage in nuclear conflict. They estimate a decade-long winter could linger after the explosions, wreaking havoc on temperatures, sunlight, and precipitation worldwide.

A Dark Decade of Winter

If nuclear war broke out between the United States and Russia, the global repercussions would extend beyond politics and trigger major climatic trauma—specifically, a nuclear winter. A nuclear winter would occur in the aftermath of nuclear blasts in cities; smoke would effectively block out sunlight, causing below-freezing temperatures to engulf the world.

To weigh the intensity of a nuclear war between two well-armed nations, the team considered the current arsenals of the two countries. They noted that important metropolitan areas—population centers or cities with strategic value, for example—would likely be targeted. And if those cities were hit, everything would likely burn.

“Even asphalt can burn at the temperatures these bombs get to,” said Joshua Coupe, an atmospheric science doctoral candidate at Rutgers University. He said these urban fires would burn everything in sight, producing “a very dirty, sooty, smoke.”

This soot, or black carbon, is the key factor in producing a nuclear winter. “What’s important about black carbon is it absorbs radiation very, very efficiently,” said Coupe. He explained that the lofted black carbon absorbs radiation and heats up and “the air surrounding it becomes very buoyant and it’s able to lift [the soot] into the stratosphere.”

If the black carbon stayed in the troposphere, it could eventually be removed by precipitation, but Coupe said that once black carbon is in the stratosphere, it can last for years, triggering a long-term, global climate response.

There are other nonnuclear events that can trigger aerosol releases into the stratosphere, including volcanic eruptions and wildfires, but Coupe noted that neither produce the same effects as soot released as a result of nuclear war.

“Volcanoes produce sulfate aerosols that don’t absorb much radiation,” he said, and “because they don’t absorb as much, their lifetime is somewhere between 1 and 2 years.”  Comparatively, he said their research shows nuclear-produced soot lasts up to a decade.

Wildfire soot can also reach the stratosphere, but Coupe noted that wildfires produce black carbon on a much smaller scale than what would result from dedicated nuclear attacks on cities. For example, the researchers state that a 2017 forest fire in British Columbia injected a few tenths of a teragram of black carbon into the stratosphere (1 teragram is 1 billion kilograms). In contrast, they estimated a nuclear war would blast 180 teragrams of soot into the atmosphere.

Climate Modeling Black Carbon

The team used climate modeling to predict what might happen to Earth after the influx of an enormous amount of black carbon into the stratosphere.

Coupe said their Whole Atmosphere Community Climate Model version 4 (WACCM4) has a much higher resolution than that found in previous studies, allowing the researchers to add more detail to predictions. Specifically, WACCM4 allowed the team to reach higher elevations, into the stratosphere—an important step in capturing lofting soot effects, said Coupe.

The team also used an aerosol module called Community Aerosol and Radiation Model for Atmospheres (CARMA) to better represent how airborne particles might grow and stick together. Coupe said using CARMA allowed the team to treat the aerosol particles more realistically.

The models show that a nuclear winter would mean an almost 10°C reduction in global mean surface temperature, extreme changes in precipitation, and a 90% reduction in the growing season across many parts of the midlatitudes.

They found that after simulated nuclear blasts, almost the entire Northern Hemisphere was engulfed in stratospheric soot within the first week. In 2 weeks, soot had invaded the Southern Hemisphere.

“That’s the power of black carbon,” said Coupe. “It lofts very high very quickly and it spreads very, very fast.”

The researchers looked at changes in global average temperatures, radiation, and precipitation over a 15-year period following a nuclear war. Coupe said their results can be summed up in one word: grim.

“Our research shows that in this U.S./Russia nuclear war scenario, nuclear winter would happen,” he said, adding that the models show an almost 10°C reduction in global mean surface temperature, extreme changes in precipitation, and a 90% reduction in the growing season across many parts of the midlatitudes.

To put things into perspective, Coupe said that the temperature change from preindustrial times to today was only 1°C. “But in nuclear winter, it approaches 10°C below the climatological mean after 2 or 3 years.”

Solar radiation, important not only for surface temperatures but also for photosynthesis, drops precipitously. Within the first couple of years of a nuclear winter, “there’s around a 75% decrease in surface radiation—which is substantial,” said Coupe.

Precipitation rates don’t fare any better, and global averages drop about 58% after soot injection into the stratosphere. Patterns of rainfall also shifted, including the weakening or disappearing of monsoons and new rainfall over desert regions.

Worst-Case Scenario

What exactly happens during a nuclear winter is a complex scenario, said Jon Reisner, a numerical modeler at Los Alamos National Laboratory. Reisner was not involved in the study but researches how nuclear weapons can affect global climate.

“The impact on climate from a nuclear exchange is still an unresolved issue,” Reisner said. He added that the researchers’ predictions appeared to be on the upper end of the spectrum for global cooling. “They’re assuming the worst, worst-case scenario,” said Reisner.

“There are dire consequences if nuclear weapons were used, not just for countries involved, but for the rest of the world.”

Reisner said he thinks the researchers are “exaggerating how much soot is being produced from fires” and noted that soot produced from urban fires is not well understood. “The big question is: What is the actual fuel loading?” He noted the intensity and duration of a fire can also affect soot production.

Although he thinks more work needs to be done to better define global climate effects, Reisner noted “at the end of the day, the direct impacts [of a nuclear war] will be significant—you can’t downplay those.”

A U.S.-Russia nuclear conflict reaches far beyond the two warring nations, said Coupe. “There are dire consequences if nuclear weapons were used, not just for countries involved, but for the rest of the world.”

Coupe hopes that their study will help inform governments and the military in their risk assessment of using nuclear weapons. “The decisions between generals could affect the entire world for years,” he said.

—Sarah Derouin (@Sarah_Derouin), Freelance Journalist


Derouin, S. (2019), Nuclear winter may bring a decade of destruction, Eos, 100, Published on 27 September 2019.

Text © 2019. The authors. CC BY-NC-ND 3.0
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