On 12 June 2026 Pugwash and the SCRAP Weapons project (at London University’s School of Oriental and African Studies) organized a multidisciplinary workshop, “Effects of a Nuclear War: Bridging Science, Policy, and Global Risk Governance” held at SIPRI, in Stockholm. The one-day event brought together natural and political scientists, legal experts, civil society and policymakers to examine the spectrum of effects of nuclear weapons use, with particular focus on the Nordic context.[1]
Key takeaways
- Nuclear weapons use should be understood as a global systems crisis, not a localised military event, with cascading consequences for health, food, climate, energy, trade, and governance.
- Global supply-chain fragility would amplify the crisis, affecting food distribution, medical supplies, transport, energy systems, and economic stability over multiple years.
- Nuclear winter effects could severely disrupt agriculture and fisheries worldwide, with Northern hemisphere high-latitude regions such as the Nordics facing especially acute risks.
- Deeper and clearer scientific understanding of the manifold consequences of nuclear weapons use should underpin better policy development.
- Public opinion in Sweden and Finland appears more sceptical of NATO nuclear deployments than current policy trajectories suggest.
- The logic of “limited nuclear war” is misleading because even a putatively ‘limited’ exchange would still be catastrophic in its consequences and could quickly escalate to the strategic level.
- Advances in climate modelling and visualization were seen as opportunities to reframe nuclear danger and enhance public communication on the global and existential risks of nuclear weapons.
The following report summarizes the discussions and anticipates a publication of selected workshop contributions to be released in summer 2026.
Full thematic report
The workshop provided an interdisciplinary lens on the consequences of the use of nuclear weapons. Across the four different sessions, participants addressed the diverse and interlinked consequences of nuclear weapons use and debated how such insights can impact the political and strategic landscape in which nuclear-armed states are expanding and modernizing their arsenals.
The workshop was organized on the premise that modern nuclear risks cannot be understood through the lens of military doctrine or deterrence theory but rather that assessment of the public health, food security, environmental, legal, and governance dimensions of nuclear use must inform military planning, governmental preparedness, and the broader public. A recurring theme was the disconnect between the different stakeholder communities, and that a deeper and clearer scientific understanding of the manifold consequences of nuclear weapons use should underpin better policy development.
The key takeaway is that the consequences of nuclear weapons use are best understood as a global systems crisis rather than a localised military event. Immediate humanitarian devastation would be followed by disruptions to food production, trade, public health, energy systems, and governance on a potentially worldwide scale—indeed, the Nordic region (and the Global North in general) would suffer disproportionate consequences. There was broad agreement that current political debate, national preparedness efforts and public understanding remain significantly out of synch with the magnitude of the risks identified, and that stronger integration of scientific, legal, humanitarian, and security perspectives is urgently needed.
Immediate effects of nuclear detonations
The workshop began with an elaboration of the physical and health impacts of nuclear explosions. The severity of destruction depends on weapon yield, burst height, and local conditions, but even a single 100-kiloton detonation could devastate urban areas several kilometres from the blast.[2] Acute radiation exposure, burn injuries, and blast trauma would cause widespread mortality, with survivors facing long-term health consequences including elevated risks of leukaemia and other cancers even decades after exposure. Presentations emphasized that no realistic systemic healthcare response exists for a nuclear detonation in a populated area, noting that in Hiroshima and Nagasaki many medical personnel were themselves killed or wounded as well as serious incapacitation of emergency and medical response systems.
The first session also examined the legacy of nuclear testing. More than 2,000 nuclear detonations during the Cold War dispersed radioactive materials worldwide, and some contaminants, such as plutonium-239, remain hazardous for hundreds of thousands of years. Participants noted that affected communities—often Indigenous, colonial, or marginalized populations—continue to experience the consequences of radioactive contamination and have frequently received inadequate compensation.
Nuclear winter and global climate effects
From study of the Hiroshima and Nagasaki atomic bombings, wildfires, and ever-more-sophisticated computer modelling, we know that large-scale fires following a nuclear weapons use on a city could inject black carbon into the stratosphere, where it would spread globally and block sunlight. In line with past modelling, which began in earnest during the 1980s, larger soot-injection scenarios would generate temperature declines (exceeding those associated with the last glacial maximum in some scenarios), reduced precipitation, ozone depletion, severe agricultural disruption, and impact on fishing stocks (which would limit the possibility of compensating for terrestrial food losses). Historical volcanic eruptions were discussed as analogues demonstrating how atmospheric aerosols can produce severe cooling and agricultural disruption.
The broader set of consequences can be grouped under what the UN Independent Scientific Panel on the Effects of a Nuclear War have termed ‘cascading’ effects.[3] Speakers highlighted the fragility of global supply chains: with the highly interconnected global market, a nuclear conflict would trigger cascading disruptions to food, energy, transportation, and economic systems, exacerbating existing vulnerabilities such as global undernourishment. One example showed how cooling climatic effects would trigger freezing over of ports in areas unaccustomed to prolonged negative temperatures—in this case, national resilience measures should include a greater investment in ice-breaker ships to mitigate a scenario in which certain food supplies become scarcer. Similarly, healthcare systems depend on complex international networks for pharmaceuticals, vaccines, and medical equipment which would be impacted over several years.
Two presentations homed in on modelling of the Nordic region to highlight specific impacts of nuclear weapons use. Due to generalized global cooling effects, Northern hemisphere high-latitude regions were identified as particularly vulnerable, with some models projecting near-total failure of staple crops over a sustained 0–5-year timeframe, as well as a dramatic decline in viable marine fisheries for several years following a major nuclear exchange. Another intervention noted that even a smaller nuclear detonation in a sparsely populated forest area such as the Karelian forest zone (midway on the Finland-Russia border) would still have major ecological and climate consequences, especially through fire, contamination, and the destruction of “European lungs”.
Participants expressed concern that research on nuclear winter effects remains significantly underfunded relative to the magnitude of the risk. Efforts to develop publicly accessible datasets and country-specific impact assessments were highlighted as important steps toward improving public understanding and policy engagement. However, participants acknowledged that the threat of a nuclear war has receded from public consciousness since the 1980s in particular, and there is some sense of attention competition as both climate change and AI dominate contemporary discussion of existential risks.
The geopolitical context and Nordic policy debate
The workshop took place against the backdrop of a deteriorating international environment, particularly in relation to nuclear arms control. NATO states and Russia now operate in a more unstable system without the same guardrails that had existed during the Cold War: the expiration of US-Russia bilateral arrangements has reduced transparency and oversight, while the increasing modernization programs of most nuclear-armed states demonstrate a weakening global nuclear governance architecture. Notably, entanglement of nuclear and conventional systems has steadily increased escalation risks and many participants agreed that this heightened risk is not understood by politicians and publics alike.
The result is a European security environment shaped less by stable deterrence and more by uncertainty, signalling, and reciprocal threat inflation. Indeed, Russia’s invasion of Ukraine was seen as the precipitating factor in the rapid shift in public opinion in both Sweden and Finland, leading to their NATO accession thereafter. Several participants argued that NATO and some European governments now frame nuclear weapons as necessary reassurance against Russian threats.[4] At the same time, participants warned that the current trends of rearmament and expanded military installations along or near the Russia-NATO borders will increase the risk of misinterpretation.
Polling figures presented by different participants highlighted a perceived disconnect between public opinion and government policy, indicating that majorities in both countries oppose the deployment of nuclear weapons on their territory while support for nuclear-disarmament initiatives remains significant. A speaker observed that the Nordic countries used to see themselves as champions of arms control and nonproliferation but are now living in a different political world. That change was described as not just ideological but as a response to fear, uncertainty, and the perceived need for stronger security guarantees vis-à-vis Russia.
Discussion throughout also highlighted the Arctic, Baltic, and northern borderlands as precarious strategic spaces, with several factors which impact Nordic signalling to Russia: Finland’s shift to legislation allowing nuclear weapons on its territory (to align with Sweden, Denmark and Norway); Finnish and Swedish participation in NATO planning; and Nordic abstentions on UN resolutions related to nuclear-war effects, with governments reportedly concerned that such initiatives could be used to challenge NATO’s deterrence posture.[5]
Legal and normative context
Within the framework of international humanitarian law, the principles of distinction, proportionality, and precaution were all raised as clear restrictions on the use of nuclear weapons, as well as the obligation to consider environmental dimensions in line with the law of armed conflict. The 1996 International Court of Justice advisory opinion was presented as establishing that nuclear weapon use would generally be incompatible with core humanitarian-law principles, while stopping short of declaring use unlawful in every conceivable circumstance.[6]
Participants discussed the recent NPT Review Conference and the continued lack of progress toward fulfilling Article VI, which obliges parties to pursue negotiations on nuclear disarmament in good faith. Indeed, the language included in drafts of the final document (which was ultimately not adopted due to several disagreements) was indicative of shifting realities concerning nuclear weapons: while a large majority of states were intent on keeping language underlining the catastrophic humanitarian and environmental consequences, the nuclear weapons states opposed what had been understood as a strong international norm.
Public communication challenges: amplifying the understanding of nuclear use
Participants argued that public discourse has increasingly normalized concepts such as “limited nuclear war” and “tactical nuclear weapons”, potentially obscuring the catastrophic humanitarian and environmental consequences of any nuclear use. There was a broad understanding that the logic of “limited nuclear war”, which persists in military and political thinking, is misleading because even a putatively ‘limited’ exchange would still be catastrophic in its consequences and could quickly escalate to the strategic level.
Effective communication should combine scientific evidence with human stories that make the impacts more tangible. Several speakers advocated reframing nuclear risk in terms of everyday human security—food, health, housing, and economic stability—rather than treating it solely as a military or strategic issue. Advances in climate modelling and visualization were seen as opportunities to create country-specific assessments that could help policymakers and the public better understand the local consequences of nuclear conflict.
[1] This workshop was organized jointly by the Pugwash Conferences on Science and World Affairs, the Finnish Pugwash Group, and SCRAP Weapons at SOAS. It is part of the ongoing Pugwash-Carnegie project on the Effects of a Nuclear War, which seeks to bring the latest scientific insights to study broader impacts of nuclear weapons in regional contexts.
[2] The atomic bomb which devastated Hiroshima on 6 August 1945 was a 15-kiloton TNT equivalent weapon, while the plutonium bomb dropped on Nagasaki on 9 August 1945 had a yield of 21 kilotons. Today’s nuclear arsenals hold a total destructive power more than 100,000 times greater, with most strategic weapons above 100 kilotons TNT equivalent each.
[3] See https://disarmament.unoda.org/en/panel-effects-nuclear-war/home. The panel will produce a report in 2027 “examining ‘the physical effects and societal consequences of a nuclear war on a local, regional and planetary scale, inter alia, the climatic, environmental and radiological effects, and their impacts on public health, global socioeconomic systems, agriculture and ecosystems, in the days, weeks and decades following a nuclear war.’ At the same time, the National Academies report (2025) highlighted a ‘system of systems’ approach to studying these phenomena. See https://www.nationalacademies.org/projects/DELS-BASCPR-21-04/publication/27515
[4] No Russian participants were present to propose alternative viewpoints.
[5] See also the Pugwash project on Nordic Security and Deterrence which explores several of the above themes.