Humanitarian Impacts of Nuclear Weapons Use in Northeast
Asia: Implications for Reducing Nuclear Risk
Executive Summary
The risk of nuclear war—that is, the risk of attacks carried out by detonating nuclear weapons,hereafter “nuclear weapons use”— as of early 2023 is judged by many observers to be at its
highest since the end of the Cold War. This risk is increasing due to nuclear threat-making
during the Ukraine conflict, the India-Pakistan conflict, the Korean conflict, and the Middle
Eastern conflict. Northeast Asia represents one of four potential flash points where nuclear
weapons might be used for the first time since the last time they were used, on Nagasaki on
August 9, 1945—hereafter called “first use” in this report. 1
Northeast Asia includes two nuclear weapons states (China and Russia), a third nuclear weapons
state with a key presence as a guarantor of security (the United States), a fourth and more recent
self-declared, if not universally accepted, nuclear-armed state (the Democratic People’s Republicof Korea, or DPRK), and two non-nuclear weapons nations under the US “nuclear umbrella”
with the technology to produce nuclear weapons and at least some voices arguing for access to or
ownership of nuclear weapons (the Republic of Korea, or ROK, and Japan). Add to this group ofactors the long-simmering and occasionally boiling issue of nuclear weapons on the Korean
Peninsula, tensions over Taiwan, and other regional disputes, and a number of potential nuclear
weapons “use cases” become plausible.
The second year of the Project on Reducing the Risk of Nuclear Weapons Use in Northeast Asia
(NU-NEA), set out to better understand the risks of nuclear weapons use in the region. To thisend, we produced quantitative estimates of the likely direct deaths and delayed cancer deaths
resulting from nuclear weapons use. Five different nuclear "use cases" were simulated andanalyzed. The hypothesized use cases were designed to be plausible, span a range of outcomesfrom a single detonation to limited global nuclear war, and include a range of nuclear actors andtargets initiated in Northeast Asia, involving the Korean Peninsula, and in some cases spreadingto other regions or continents. The estimated deaths and radiation-induced cancers resulting fromthe following six impacts were evaluated:•Thermal fluence (heat) from nuclear blasts.

•Firestorms: multiple fires lit by thermal fluence that coalesce into large-area
conflagrations encircled by hurricane-force winds as the heat rising from the fires pulls

1 There is no legal or institutional definition of Northeast or East Asia. The United Nations Economic and Social

Commission for Asia and the Pacific (UNESCAP) uses “East and North East Asia (ENEA) to refer to “China;
Democratic People's Republic of Korea; Hong Kong, China; Japan; Macao, China; Mongolia; Republic of Korea”. See
UNESCAP (undated), “4 List of countries in the Asia-Pacific region and subregions”, available ashttps://data.unescap.org/dataviz/methodology/list-of-countries-in-the-asia-pacific-region-and-subregions.html
An examination of the contested usage related to “Asia” and its sub-regions is found in P. Hayes and C.I. Moon, ed(2018), The Future of East Asia, Palgrave MacMillan, available at: https://link.springer.com/book/10.1007/978981-10-4977-41

cooler air in behind it. Physical damage caused by blast overpressure provides fuel for
firestorms, which could burn for weeks.
•Blast overpressure, causing building damage and collapse.

•Prompt radiation from the nuclear detonation itself.

•Fallout radiation, as radioactive material from the blast and contaminated debris are
spread by wind and rain.

•Radiation-induced cancer deaths suffered by those exposed to prompt and fallout
radiation but not killed by the nuclear blast immediately or in the short term (withinseveral months to a year).

Out of the 30 plausible use cases developed in Year 1 of the NU-NEA project, five use cases
were simulated and evaluated quantitatively:
1. “We’re Still Here” Variant 1, involving nuclear weapons use by the DPRK followed by
the United States, with 3 total detonations of 10 kT (kiloton) and 8 kT weapons.
2. “US Leadership Hubris,” involving first nuclear weapons use by the United States,
followed by use by the DPRK, and China, with 18 total detonations ranging in yield from
8 to 300 kT.
3. “Use by Terrorists” Variant 1, with one 10 kT weapon detonated by a terrorist group.
4. “Conflict from Ukraine Spreads East,” involving first nuclear weapons use by Russia andfollowed by the United States, totaling eight detonations of 8, 150, and 200 kT weapons.
5. “Not Going Well in Taiwan,” involving first nuclear weapons use by China followed byresponses from the United States, with a total of 24 detonations ranging in yield from 8 to300 kT.
The table below summarizes the estimated prompt and short-term deaths and radiation-induced
cancer deaths resulting from the impacts above for each of the five use cases evaluated. Even in
the most limited of nuclear conflicts, deaths were in the tens or hundreds of thousands, with themore extensive conflicts resulting in millions of deaths and hundreds of thousands of cancer
deaths. It should be noted that even the most extensive conflicts evaluated here were halted shortof an all-out exchange of intercontinental nuclear missile attacks, but certainly could have ended
that way. In the table below, “prompt” deaths are those caused by physical damage or fires in theimmediate aftermath of detonations, including victims not killed immediately but dying withindays or weeks, and “short-term” deaths include victims who succumbed to their injuries within
the year following the nuclear attack.

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Estimated Likely Direct and Cancer Deaths in Each of Five Modeled Use Cases2

These results show that use cases that include many high-yield (50-300 kT) airbursts result in ahigher relative impact, roughly 35% lethality, than use cases with a limited number ofdetonations or with mostly surface-bursts, which average roughly 25% lethality. As a conflictescalates, especially when progressively larger nuclear detonations target more populated areas,
the humanitarian impacts of a nuclear conflict not only increase, but often grow by orders ofmagnitude. One contributing impact is the occurrence of deadly firestorms resulting from highyield weapons detonated as airbursts that cause far-ranging thermal fluence, demonstrating thatfirestorms can be a significant contributor to the lethality of nuclear weapons. Furthermore, evenuse cases with a limited number of surface-bursts or using weapons of relatively low yield cancause a disproportionately high number of fatalities when acute health effects from highradiation doses and long-term cancer deaths are considered.
In Use Case 3, for example, a single surface-burst in an urban area results in estimated cancer
fatalities on the same order of magnitude as the limited global nuclear war cases shown in Use
Cases 2 and 5. The death toll in the short-term from exposure to high fallout radiation could also
be the same or higher in Use Case 3, even though only one nuclear weapon has been detonated inan urban area. This result emphasizes how unpredictable the long-term and health impacts ofnuclear use cases can be because it is nearly impossible to foresee whether a conflict will end
after one detonation, 18 detonations, 24 detonations, or more, and whether urban areas will betargeted. Even when the conflict does not escalate to global nuclear war, it is possible that
impacts consistent with those expected in a global-scale nuclear war can be felt after only one
nuclear detonation.
In addition to devastating losses of human life, a range of economic and societal impacts, such as
billions of dollars in infrastructure damage and health care costs, and a further set of global,regional, and local ecological impacts such as climate effects or effects on oceans, would also
result from these use cases. The evaluation of these and other impacts will be addressed in thethird project year.
The use cases evaluated in the NU-NEA project are intended to be plausible, but they capture
only a small fraction of the possible pathways to nuclear war and its consequences identified in
2 Note that Individual impacts in this table may not add up to the exact total shown in column five due to rounding.

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this project, which in turn do not even begin to encapsulate the universe of possible ways that anuclear conflict could start and play out. Several conclusions, however, can be drawn from thelimited number of use cases evaluated in this project:•A nuclear conflict based on regional issues can escalate to a global nuclear conflict within
hours or days after the first use of nuclear weapons.

•Any nuclear detonations, even in relatively unpopulated areas, are likely to result in atleast thousands of deaths, with possible fallout crossing international borders, causing
additional health risks and increasing political tensions even when fallout levels are low.

•Even when focused on military targets, nuclear detonations may kill many hundreds ofthousands of people within days or months, as well as cause hundreds of thousands ofadditional cancer deaths and great economic damage.

•The impact of mass fires or firestorms that sometimes result from nuclear explosions cansurpass the lethality of other direct impacts of nuclear use. Historically, military planningfor nuclear use has lacked sufficient consideration of firestorm impacts.

•Many of the plausible nuclear use cases developed for this project have their genesis in
misinterpretation of intentions and lack of communication between adversaries,
underscoring the need for communication between nations to avert nuclear weapons use,
especially during times of conflict and crisis.

•There are many plausible pathways to nuclear war that would have cataclysmic effects.
Most of these pathways involve “slippery slopes” of descent into nuclear war, where anaction by one party is misinterpreted by another, leading to conflict escalation thatproceeds further and more rapidly than adversaries intend or foresee. As such, thesepotential pathways to nuclear war are often invisible to policymakers.

•It is urgent to reduce the risk of choosing or stumbling onto one of these pathways bydeveloping and applying regional and global policy measures such as increasingtransparency of nuclear stockpiles, deployments, and operational and declaratory
doctrine—especially relating to integration of nuclear firestorms into nuclear targeting—such as increasing communications with nuclear hotlines.

•In addition, it is important to explore policy measures to reduce the role of nuclear
weapons in security policy and to revive arms control and disarmament diplomacy. Suchmeasures include introducing a nuclear no-first threat norm; resolving regional conflicts;
and, ultimately, establishing a regional security framework including denuclearization of
the Korean Peninsula and a nuclear weapon free zone in the region towards eliminationof nuclear weapons altogether.

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