Under the Nuclear Cloud

The US Air Force plans to deploy new land-based nuclear missiles, named Sentinels, in existing underground concrete silos spread across five states and keep them there for the next 50 years or more. The Air Force expects the missile silos to be targets of nuclear attack. Such an attack would generate large amounts of radioactive fallout across North America. No up-to-date information about the resulting risk to public health and the environment has been made available to the public.

Based on hundreds of simulations of the consequences of nuclear attacks on the US missile silos, Under the Nuclear Cloud presents for the first time the possible consequences for the public of a concerted nuclear attack on US missile silos. It reveals the communities that are most at risk from fallout in the United States and Canada given average wind and rain patterns across North America.

Under the Nuclear Cloud is produced and supported by the Brown Institute for Media Innovation and the Princeton Program on Science and Global Security.

Methodology

US Air Force Environmental Impact Statement

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On March 31, 2023 the US Air Force released the final version of its Environmental Impact Statement (EIS) for the Sentinel program.

Mandated by the National Environmental Protection Act (NEPA) of 1969, the two-volume, 3000-plus page document is meant “to analyze the potential effects on the human and natural environments from deployment of the Sentinel intercontinental ballistic missile.” The document does not discuss the risks associated with nuclear attacks on the Sentinel missiles, however.

About 300 people attended seven in-person meetings organized by the Air Force in communities living close to nuclear silos in Colorado, Nebraska, Wyoming, North Dakota, and Montana as well as two webinars to collect public comments on the Sentinel EIS. Only 24 people in total gave comments. This means one in 10 million American adults that could experience lethal doses of fallout from a nuclear attack on the ICBM silos made their opinions known.

Under the Nuclear Cloud details the potential fallout risks in the 7 locations where the US Air Force organized in-person public hearings to collect comments on the EIS. It also indicates the radiological risks for federally recognized tribal lands that are home to 63 Native American tribes that the US Air Force engaged separately to mitigate the impact of the Sentinel program on their cultural resources.

Fallout data

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To produce Under the Nuclear Cloud, we simulated the radioactive fallout resulting from a concerted nuclear attack on the 450 US missile silos 365 times, once for each day of 2021.

Each silo is targeted with one warhead generating an explosive yield of 800 kilotons of TNT equivalent. Each nuclear explosion is assumed to take place at ground level (known as ground bursts) and generates a 16.8-km tall radioactive debris cloud.

The radioactive cloud is assumed to consist of micron-size silica particles (density of 2.5 g/cm³) exhibiting a log-normal size distribution with a mean diameter of 0.407 micron and a geometric standard deviation of 4. We use a gravity-sorting algorithm to distribute the particles along the vertical axis of the stabilized cloud according to their size and the yield of the explosion.

To generate the fallout data, we use the US National Oceanic Atmospheric Administration HYSPLIT atmospheric particle transport code together with weather data from the Global Data Assimilation System (GDAS1) one-degree archive.

Based on hundreds of simulations of the consequences of nuclear attacks on the US missile silos, Under the Nuclear Cloud presents for the first time the average consequences for the public of a concerted nuclear attack on US missile silos. It reveals the communities that are most at risk from fallout in the United States and Canada given average wind and rain patterns across North America.

Under the Nuclear Cloud is produced and supported by the Brown Institute for Media Innovation and the Princeton Program on Science and Global Security.

Generation of the HYSPLIT input files (control and initial particle position files) and processing of the HYSPLIT output data were conducted using the Nuclear War Simulator software and QGIS.

Fallout are tracked across North America for 48 hours and the outdoor cumulative dose to the public is integrated over four days. The greater the dose, the higher are the chances that deaths occur among the exposed population. According to our calculations, 1 to 2 million people could die on average as a result of a concerted attack on the US missile silos, assuming they are able to shelter with food and water for several days.

Cumulative Dose, Fatality Rates

In practice, not all locations will be impacted at the same time. The actual impact of a nuclear strike on the silos will depend on the meteorology, including wind speed, direction and rain, at the time of the attack. The map shows the average outdoor radiation dose across North America after four days of exposure, averaging the impact of shifting winds across the 365 simulation we ran with weather data from 2021.

Communities living closest to the silos could receive a dose several times greater than what scientists consider lethal. Most inhabitants of Montana, North Dakota, South Dakota, Nebraska and Minnesota would get average doses greater than 1 Gy, causing fatalities from acute radiation syndrome, especially among at-risk populations. Any dose above 0.1 Gy would lead to significant increase in cancers in the exposed population. Overall, most people living in the contiguous United States are in areas where the average dose is greater than 0.001 Gy per year, the current limit of exposure to the public. Our calculations make no assumptions about access to health-care or emergency services. Nor do they include other sources of exposure such as prompt radiation from nuclear explosions.

To learn more about the methodology and software stack used to generate the fallout data, see this related publication: Philippe, Sébastien, and Ivan Stepanov. Radioactive Fallout and Potential Fatalities from Nuclear Attacks on China’s New Missile Silo Fields." Science & Global Security (2023): 1-13.

To learn more about the effects of high radiation exposure, see this fact sheet from the Center of Disease Control and Prevention.

Credits

This map was created by Katie Watson with data produced by Sebastien Philippe, Ivan Stepanov, and Svitlana Lavrenchuck.

It was supported by The Brown Institute for Media Innovation at Columbia Journalism School and Stanford Engineering School, as well as the Princeton Program on Science and Global Security.

It is part of the Missiles on Our Land, a broader multimedia project published in partnership with Scientific American.

silo Nuclear missile silos
American Indian reservations
hearings
Locations of in-person public hearings
silo Nuclear missile silos
American Indian reservations
hearings
Locations of in-person public hearings

UNDER THE NUCLEAR CLOUD

This map visualizes the average risk of radiation exposure for a large portion of North America in the event of a concerted nuclear attack on US missile silos. It is based on computer simulations for each day of 2021 of the fallout that would result from such an attack on that day.

The color represents the average outdoor radiation dose after four days of exposure. Communities living closest to the silos could receive doses greater than 8 Grays [Gy], which scientists regard as lethal.

CUMULATIVE DOSE GRAY

Cumulative Dose, Fatality Rates

This map highlights the seven communities where the Air Force presented the Sentinel environmental impact assessment in person. It also shows where the Air Force sought tribal input on sites and objects of tribal significance.

Most of these communities are in areas where significant fatalities from acute radiation syndrome would be expected in case the silos are attacked.

The average outdoor external dose over four days here after an attack would be 0 Gy. Each bar below shows the percentage of days in 2021 for which the radiation dose would fall within a certain range.
Exposure to doses greater than 1Gy would lead to near-term fatalities. Doses of 4 and 8 Gy are lethal in about 50% and 99% of cases, respectively. Doses below 1 Gy lead to longer term health risks.