Workshop on Nuclear War/Winter & NZ: Wellbeing of millions and $1 trillion plus at risk, strategic resilience must become bread & butter NZ policy

Matt Boyd, Ben Payne, Nick Wilson

Photo by Rod Long on Unsplash


  • We held a workshop on the risk of nuclear war/nuclear winter and implications for Aotearoa/NZ on 9 February 2023.
  • The workshop was attended by 20 experts representing organisations in the public and private sector, and academia.
  • Attendees discussed our new NZ Nuclear War Hazard Profile * and deemed the key scenario to be both ‘quite plausible’ and ‘catastrophic’.
  • Elicitation and sharing of key knowledge underscored the severe and wide-ranging impact of a Northern Hemisphere nuclear war for an isolated non-combatant nation like NZ.
  • Resilience measures are likely to be possible, but research to understand the cascading impacts through NZ industry and society is needed.
  • Also needed is a long-term big-picture strategic view of how resilience measures can improve wellbeing now and mitigate a wide class of risks including extreme weather or future severe pandemics.
  • Next possible steps for better understanding NZ’s resilience and vulnerabilities were identified (see bullet points and numbered list at end).

*Note: some readers report this hyperlink not working, the url is:

Resilience: NZ’s Bread & Butter

Global catastrophic risks such as nuclear war could result in long-term harm on a global scale, with profound disruption to our way of life in Aotearoa New Zealand (NZ). Other global risks including extreme pandemics, supervolcano eruptions, catastrophic solar flares, abrupt climate change, and many others are named in the new US Global Catastrophic Risk Management Act which requires analysis and planning for major impacts. Resilience to such risks to protect people now and ensure flourishing of future generations requires more than ‘stacks of tuna cans.’ Wise strategy, investment in risk analysis, planning, quality infrastructure, resilience, and cooperation can help optimise the path forward. This should be bread and butter policy in the 21st century.

New Zealanders have seen first hand the impact of catastrophe in recent weeks. Severe flooding and cyclone damage reveal what happens when regions are cut-off and government response is stretched thin. In a global catastrophe, all of NZ could be isolated making response difficult. We need to ensure that as a nation we can get through such catastrophe by developing national and local resilience ahead of time.

Aotearoa NZ Catastrophe Resilience Project

Using nuclear war as a representative global catastrophe, the Aotearoa NZ Catastrophe Resilience Project seeks to understand NZ’s vulnerability and resilience factors and recommend initiatives to mitigate global catastrophic risk.

The Aotearoa NZ Catastrophe Resilience Project Plan

Hazard Profile

The first step in building resilience to global catastrophe is to analyse the hazards. Using the methodology of national risk assessment, we developed a Nuclear War/Winter Hazard Profile for Aotearoa/NZ.

The profile describes ‘significant’, ‘major’ and ‘extreme’ nuclear war scenarios. The ‘major’ scenario is then analysed in depth.

Major Nuclear War Scenario

In the ‘Major’ scenario 250–500 nuclear weapons of 10–100kT are detonated, many on cities. This results in 10–30 teragrams (megatonnes) of soot rising into the stratosphere. This soot blocks the sun and causes -4.0 C of mean global cooling. Simultaneous conventional attacks mean mass destruction of Northern Hemisphere infrastructure. 30–75 million people are killed immediately. Weeks of chaos follow as radiation disperses, deaths mount, normal business and trade functions halt, and communications are destroyed. The global temperature drop lasts into the following years. Food production in North America, Europe, and Russia falls 60-90% in the second year.As regional famines take hold, countries turn inwards, hoard commodities, and global trade is severely disrupted. NZ suffers from massive trade disruption and some modest impact on crop production (from cooler temperatures and reduced sunlight).  The Hazard Profile accounts for 12 key impacts and two plausibility factors (based on a Swiss methodology). Together these allow this hazard to be plotted on a likelihood vs consequences diagram (see below).

February 9 Workshop

We ran a workshop on 9 February 2023 to help validate the nuclear war/winter hazard profile for NZ. The workshop included a pre-workshop activity to estimate the impact and plausibility of the ‘major’ scenario. Expert elicitation activities on the day allowed us to gather and aggregate informed input to refine the Hazard Profile.

The workshop consisted of diverse representatives across public and private sectors, as well as academia. Attendees included experts on global catastrophe, nuclear war, emergency management, and societal systems. The workshop included presentations on national risk assessment and nuclear war, as well as discussion of impacts, plausibility and knowledge gaps.

A lot of brainstorming and expert input took place both in the room and in the Zoom chat.


Overall, the original ‘Major’ scenario was considered relatively conservative. Outcomes could be worse due to the logic of escalation in a nuclear conflict, likely targeting of industrial capabilities, loss of cloud/digital systems and cascading impacts across all industries.

The likely scenario could result in many fatalities in NZ due to a range of mechanisms including shortages of imported medication. There could be widespread illnesses, including mental health issues, and widespread societal impacts.

The anchor points for economic harms experienced by NZ used in national risk assessment were seen as too conservative (designed for floods, earthquakes, etc). The reality could far exceed NZ$1 trillion in monetised equivalent value loss irrespective of impact on factors such as environment or culture. The potential for electromagnetic pulse (EMP) as a strategic warfare method should not be discounted. Although NZ has held a longstanding anti-nuclear stance, the nascent space industry and existing formal military alliance with Australia (and more informal military links with the US), may be seen as a threat and could lead to NZ being targeted (albeit some participants thought this very unlikely). It was also considered necessary to build a ‘reasonable’ timeframe into the scenario, as a reference point to calibrate thinking on impacts.

Participants rated the impacts the ‘major’ nuclear war scenario would have on NZ using a 0–8 scale anchored with descriptors, where each point increase represents a 3x magnitude increase in impact. The following graph summarises the participants thinking on impact levels, and the table quantifies this scale in concrete harms and monetised value (again using the Swiss methodology). A separate table provides a high-level summary of key contributions.

12 Impacts of a Northern Hemisphere nuclear war on NZ

The 12 impacts quantified (mean of expert estimates, n=14)

The NZ$1 trillion plus risk

When the diverse impacts of the ‘major’ scenario are converted to monetary terms (a necessarily highly speculative activity) to allow comparison with other risks, the harm to NZ from a Northern Hemisphere nuclear war would likely exceed NZ$1 trillion. But this ‘mean’ total value doesn’t capture the distribution – with some expert respondents suggesting that the impacts would be very much higher than the top of the scale in multiple domains.


Agential or unprecedented risks, which lack a historical data set or depend on fluctuating willingness to act, such as nuclear war, can be classified according to the plausibility of the specific scenario being considered (ie, the ‘Major’ scenario outlined above). 

In this case, plausibility was construed by combining estimates of the degree of intent and ability possessed by likely perpetrators of nuclear war, with the technical and operational feasibility of the scenario. Following discussion, independent estimates were aggregated and the scenario was estimated to be ‘quite plausible’ at a mean of 3.39 on a 1–5 scale with 0.5 point increments.

Key to the plausibility assessment was the fact that a wide range of nuclear risk variables are trending in the wrong direction, these include: the number of weapons, modernisation of systems, increasing conflict, cyber threat, intermixing of command and control systems, terrorist threats, the desire to acquire weapons, plus the existence of historical near misses.

The resulting plausibility of the ‘major’ scenario is mapped to the estimated impact in the following risk diagram.

Figure Legend: The figure displays the plausibility assessment for the ‘major’ scenario mapped against the impact assessment (using an established Swiss methodology). The circle indicates the mean of independent assessments of diverse experts (n=14) conducting a pre-workshop activity. The arrow indicates that the assessment moved towards a higher impact category (~$1 trillion plus monetised harm) following workshop interactions with diverse other experts (n=12).


Workshop participants indicated that several of the impact categories in the Hazard Profile were hard to quantify. There was some suggestion that quantification is not necessary if the scenario is clearly in the ‘upper right’ section of the risk diagram (ie, plausible and highly damaging). However, some quantification seems useful as a first step to place it in the upper right part of the risk diagram and therefore to distinguish it from more minor hazards.

Other ‘upper right’ quadrant risks

It is interesting to compare the location of the ‘major’ nuclear war scenario in the upper right (ie, quite plausible and extremely damaging) region of the risk diagram to the glaringly obvious ‘upper right’ risk identified in a NZ national risk assessment that pre-dated the Covid-19 pandemic and the Cyclone Gabrielle disaster (but post-dated the Christchurch Earthquakes and the 1918 pandemic – the highest impact natural hazard in NZ’s history where over 8000 NZ citizens died).

A historical NZ national risk assessment

Source: DPMC NZ’s National Security System Sept 2011

Some key themes of workshop discussion

The following represent just some of the key insights that workshop participants contributed and which the Aotearoa NZ Catastrophe Resilience Project will be following up.

  • Compared to findings of previous 1980s work on nuclear war impact and NZ, the impact of damage to the internet, overseas-based cloud data, and digital communications featured prominently. It is unclear to what degree the internet, cloud data, and digital communications would be operational in the ‘major’ scenario. This is a key area for research and interviews with experts as it has serious implications for the operational potential of government, industry, and personal life.
  • The risk to NZ’s territorial integrity is very uncertain. It is possible that refugees, non-state actors, hostile state actors, or powerful individuals attempt to reach NZ (just prior to or after such a nuclear war). It is also possible that there are insurmountable difficulties of doing this under the conditions of the ‘major’ scenario. This is another key area for further analysis.
  • The possible collapse of the financial system and likely shortages including transport/fuel, might mean that a key response to the ‘major’ scenario may be quick transfer of power/agency to local government and local communities. However, planning to ensure that such agencies/groups have access to the raw materials and knowledge required to ensure food supply, alternative energy supply, and communications may be needed. A detailed analysis of these requirements would probably be useful.
  • Several workshop attendees emphasised the need for a NZ narrative around resilience to major global catastrophe, fostering public discussion of these risks, with emphasis on the need for cooperation to achieve strategic resilience. Fostering such a narrative could be a very worthwhile government action if it focuses on opportunities for enhanced wellbeing now, as well as building resilience against other hazards (eg, severe storms associated with climate change).
  • The principles of Te Tiriti o Waitangi and the knowledge and perspectives of Māori are likely to aid strategic resiliency to major global catastrophes and to strengthen local level resilience for a wide range of other hazards.
  • Further analysis of the ‘major’ scenario and other global hazards would not cost much in comparison to large infrastructure projects such as Transmission Gully and could form part of an expanded National Science Challenge on resilience to hazards, or a new national science ‘mission’.

Additional decision-relevant information

Our nuclear war/winter Hazard Profile notes that nuclear war is a representative risk and other global catastrophes could produce conditions with functionally similar impacts on NZ, perhaps requiring common resilience measures. These hazards should also be assessed and include:

  • Solar flares (that threaten nearly all electronic infrastructure)
  • Major volcanic eruptions (that cause volcanic winter)
  • Asteroid/comet impacts (that cause global sunlight blocking)
  • Conventional Great Power conflicts
  • Extreme pandemics (eg, from bioweapons)

There is a plausible risk of collapse of both technological and industrial society following a major global catastrophe. Prospects for recovery following such collapse are unclear and societies could stagnate at low technological levels with chronically low levels of wellbeing. This possibility increases the salience of these risks.  

NZ is plausibly one of the countries in the world most resistant to the physical and climatic impacts of nuclear war (see our recent publication on this). This privileged position is reason for NZ to ensure resilience to the likely impacts, thereby maintaining a hub of functioning industrial/social complexity for the sake of humanity. Our country could have an inspirational ‘out of the ashes’ story to tell.  

Next Steps

This workshop took place in the context of recent global research on the public’s increasingly hawkish views on nuclear conflict. A recent study found that support for the use of nuclear weapons under certain circumstances has risen in the Netherlands and Germany from before to after the Russian invasion of Ukraine. Similarly, another study from the Cambridge Centre for the Study of Existential Risk published in 2023 found that informing people about the possible devastating impacts of nuclear winter reduced their support for nuclear weapon use. There appears to be a role for open discussion about the implications of nuclear war and the use of opinion polls on global catastrophe and resilience, especially in a NZ election year.

The Hazard Profile we have produced should now be connected to a capabilities assessment. This is an assessment of how, specifically, the conditions resulting from a ‘major’ nuclear war would have downstream impacts on NZ sectors and way of life, and how domestic activity could be adapted to preserve systemic functions. 

Next, we move into a survey and interview phase of our research to address these questions. We plan to hold additional workshops once results of these studies have been compiled. These discussions will form a foundation for policy recommendations and resilience options that central government, local government, communities, and private industry could consider.

In the meanwhile, there are concrete actions that central government could take to reduce NZ’s risk to major catastrophe in the longer term. Indications at our workshop were that participants felt these actions are “bread and butter policy” and functions that citizens expect of government. Some examples are that central government could:

  1. Work to combine existing narratives in government work on food system security, energy security, communications security, etc, into an overarching narrative of building resilience across interlinked systems to mitigate both catastrophic risks and increasingly routine risks.
  2. Develop and provide information about major risks such as nuclear war/winter and other global catastrophes to the public and decision makers. This is because such information has an impact on people’s beliefs and actions and could aid wise decision making. Our workshop showed that when experts shared information the group’s average assessment of risk rose.
  3. Reframe the upcoming draft NZ National Security Strategy so that it focuses less explicitly on ‘malicious threats’ and more on ‘resilience and vulnerability’ to both catastrophic risks and more routine risks (eg, large storms).
  4. Allocate resources to research and analyse specifically the issue of territorial integrity following a major global catastrophe and a plan to manage likely situations (both aiding refugees in need and protecting the wellbeing of NZ’s citizens).
  5. Allocate resources to research and analyse specifically the issue of whether and how government and the financial system could continue to operate in a context of no internet, no access to cloud data, and no digital communications. What are the required resiliency measures needed to minimise cascading degradation in governance and financial security?  

Our 9 February 2023 workshop on the nuclear war/nuclear winter hazard and Aotearoa NZ has provided a fascinating and practical foundation for the next phases of our Aotearoa NZ Catastrophe resilience project. We again thank all the workshop participants and welcome any further feedback on this blog post and the work to date.

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