Food for thought: Frost resistant crops to hedge against the impacts of nuclear winter

By Matt Boyd, Ben Payne, & Nick Wilson

Image: Midjourney


  • The risk of nuclear war is probably rising due to geopolitical tensions and modernisation of nuclear arsenals.
  • New Zealand (NZ) would suffer severe consequences, including trade collapse, shortages of liquid fuels, and potential nuclear winter effects.
  • Nuclear winter could lead to reduced agricultural production and necessity of growing frost-resistant crops.
  • NZ has good potential to produce food in a nuclear winter if optimal strategies are followed.
  • In our just published study, we analysed frost resistant crops to estimate the minimum cropped land area to meet food needs of the NZ population.
  • Wheat and carrots are the most efficient frost resistant crops for food supply, but a range of other cereal and vegetable crops were also identified.
  • Pre-catastrophe analysis, a cooperative national approach, and a national food security strategy are needed for ensuring food security.
  • Ensuring food security for one global catastrophe will likely help with food security for other scenarios such as climate change, deglobalisation, or industrial collapse due to eg, major volcano, global conflict, or solar flare.

Technical paper in Scientific Reports here

Summary video

Risk of nuclear war

The risk of nuclear war is plausibly rising due to geopolitical tensions, active warfare, expansion and modernisation of arsenals, and erosion of international arms control agreements.

Some nations would be devastated by direct targeting with nuclear weapons, but others such as NZ, would likely suffer severe secondary consequences due to collapse of trade and potentially the onset of a ‘nuclear winter’.

Climate modelling studies suggest that a nuclear winter (blocking sunlight and reducing crop yields) could be catastrophic. Agricultural production could fall 8–61% in NZ.

Importantly there could be a large increase in the number of frost days. There is historical precedent as summertime frost occurred in Europe, China, and North America following the eruption of Mt Tambora in 1815.

Compounding the climate impacts could be shortages of liquid fuel. This is because NZ is 100% dependent on imported liquid fuels. The government has recently mandated 21 days of diesel reserves are stored onshore (with another 7 days to be stored by the government) but this fuel might quickly run out.

Communications difficulties due to internet and satellite disruptions could make coordination of a response difficult.

NZ is a very good food producer and exports far more food than is needed by the domestic market, mostly in the form of dairy products, as well as meat and fruit. In one analysis, we found that export dairy alone could provide over three times the daily energy requirement for all NZers if it could be directed to the domestic market.

However, in a context of scarce liquid fuel to transport milk daily, and impaired pasture growth due to low average temperatures, along with possible limitations to long-distance communication and coordination, it may be preferable to prioritise production of other food sources.

Our new study

Given the possible scenario above, we conducted an optimisation study to assess the minimum arable land use required, specifically for frost resistant crops, to supply the food needs of all NZers. We required that the analysis satisfy both dietary energy and dietary protein requirements.

We restricted the analysis to frost resistant crops because a nuclear (or volcanic, or asteroid/comet) winter could make winters more severe and add many additional frost days to the year.

NZ food needs

The estimated dietary energy intake of the entire NZ population has previously been estimated at 44.4 billion kJ per day, equivalent to 8686 kJ (2076 kcal) per person per day. Using nutritional survey data, we calculated the protein intake to be 413 tonnes per day (81g/person).

Image: Midjourney

Frost resistant crops

Frost resistant cereal crops such as winter wheat can take better advantage of the early spring growing season than their spring planted equivalents. They are typically relatively efficient sources of food energy and are usually much cheaper to produce than dairy products, meat, and fish. Other frost resistant crops include carrots, sugar beet, onions, cabbage, and so on. High yield crops such as potatoes were excluded because the foliage is frost-sensitive. You can see details of various crops and their resistance to frost in our published table.

In one scenario we aimed to supply sufficient calories and protein solely through frost resistant crops. In another scenario, we considered 50% of nutritional needs supplied from frost resistant crops and the rest from other food sources (that might still be produced but with decreased yields, eg, frost sensitive crops in greenhouses, or grass fed livestock products).

Comparisons were made with the total area of crop land used in 2019 in NZ, which was 132,717 hectares in horticulture and 487,763 hectares in grain.

Our results

We found that wheat (97%) and carrots (3%) was the best combination of crops when optimising for minimal land use. Wheat provides 1400 kJ and 13.4g protein per 100g. Standard yields in NZ are around 9.9 tonnes per hectare (vastly more than Australian yields). Carrots provide only 156 kJ and 0.6g protein per 100g but can yield a massive 120 tonnes per hectare.

As a baseline, wheat and carrots could provide all the dietary energy and protein for the NZ population using 116,000 hectares of land, which is equivalent to 19% of the current cropping land used for all crops.

However, the impact of nuclear winter on sunlight reaching the ground means that these yields could be reduced by up to 61%. In such a scenario NZ would need 297,000 hectares of wheat (48% of current cropping land) or 149,000 hectares assuming 50% of food could still come from non-wheat/non-carrot sources.

The least efficient use of land to produce dietary energy was grass-fed lamb which was 310 times less productive in dietary energy per hectare than carrots (beef was the next most inefficient).

The least efficient source of protein was also lamb which was 62 times less productive in dietary protein per hectare than wheat (beef, then milk, were the next least efficient).

The following table appears in our paper and illustrates the minimum land area required across various scenario combinations (link to published table).

NZ already grows a range of frost resistant crops. However, current levels of production were estimated to be capable of providing 74% of the dietary energy of the population in the no nuclear winter scenario (ie, leaving a 26% shortfall). But this level of provision was only 29% for the severe nuclear winter scenario (ie, leaving a 71% shortfall).

This means that if there was a substantial increase in the frost period (likely with a severe nuclear winter), then frost resistant cropping may need to be scaled up in NZ. Our results suggest that planting wheat and carrots are likely to be an efficient approach. Nevertheless, in reality there would likely be specific climatic/soil conditions that would make other crops more efficient in particular localities eg, onions in Pukekohe, oats in parts of Canterbury.

Agricultural energy inputs

We have so far considered only land area, frost resistance, yield, and dietary requirements. Wheat typically requires additional processing post-harvest (though can be cooked and eaten as a grain) and an analysis of all energy inputs may find other frost resistant crops to be the most efficient in a context of severe energy insecurity.

The Energy Efficiency and Conservation Authority estimates that the agriculture sector in NZ uses 295 million litres (L) of diesel per year, with sheep and beef farming using the most (108 million L, [37%]), followed by dairy farming (95 million L, [32%]).

NZ’s new requirements for diesel reserves amount to about 270 million L  (when tallying commercial requirements and new government reserve requirements).

Even with the strictest prioritisation and rationing, the reserves could barely keep the current agricultural sector running for one year, let alone the rest of the economy including essential services.

In a protracted catastrophe (and nuclear winter could last a decade), rational prioritisation of liquid fuel use within the agricultural sector would be needed. Wheat and carrots appear promising within these constraints and could be grown near population centres and along electrified railway networks.

Image: Midjourney

Wheat production has many benefits

For food, NZ mostly produces milk products, meat, and fruit (all mainly for export markets). Whereas much NZ bread is made from wheat sourced from Australia. In part this is because it is cheaper to transport grain in bulk from Australia to Auckland than it is from the South Island to other locations in NZ where flour is produced.  

NZ wheat production in 2021 was 43,500 hectares. Processing capacity appears to exceed this given the milling of Australian grains locally. Only one flour producer (Farmers Mill in South Canterbury) sources grain entirely from NZ farms, which is about commercial objectives of allowing manufacturers and bakers to pass on the promise to their customers of baking from 100% NZ grown wheat for a 100% NZ made product.

Economies of scale mean that a handful of foreign owned flour mills in NZ process most of the wheat, yet as recently as the 1980s NZ was self-sufficient in wheat production and operated 30 or 40 mills.

In a no-trade scenario NZ might need to return to increased grain production to allow for a flexible diet.

Additionally, in a world where there appears to be a trend towards deglobalisation and towards regionalism, more countries might have to start scaling up their own wheat production. Expanding the amount of wheat cropping now would provide a suite of resilience benefits across a range of trends and risks.

Benefits of wheat production:

  • Greater food security in a world where supply chains are vulnerable.
  • Greater food security in a deglobalised and regionalised world.
  • Greater food security in a catastrophe situation (eg, nuclear war), if global trade collapses abruptly.
  • Greater food security if another abrupt sunlight reducing catastrophe occurs, such as volcanic winter, or asteroid/comet impact winter.
  • Substitution of animal food sources with high greenhouse gas emissions for grain production with lower emissions.

Wheat also has the advantages of not requiring refrigeration, being relatively energy dense (which reduces food transportation costs), and excess can be fed to livestock (eg, chickens for egg production).

However, more work is needed to understand the yield of wheat (and other frost resistant crops) in various regions under nuclear winter conditions, and the impact that the absence of imported agrichemicals (including fertiliser, herbicides, pesticides, and fungicides) would have. This analysis will be important as there are virtually no agrichemical facilities left in NZ (just an ammonia-urea plant that makes fertiliser).

The greater the impact of nuclear winter, and the more constrained the supply of agrichemicals, the more land is needed to feed everyone and the greater the consumption of precious liquid fuels.

Next Steps

To enhance resilience, NZ should conduct locally-specific climate modelling for nuclear winter scenarios, incentivise frost-resistant crop production in normal times, and analyse the feasibility of a local frost resistant crop seed stockpile.

Vulnerabilities of agriculture to disruptions in infrastructure and critical inputs must be identified and addressed.

Further analysis, exploring crops under catastrophe conditions (eg, extreme climates and a lack of agrichemicals), is essential and coordination and collaboration through a non-partisan government centre for mitigating extreme risks could ensure comprehensive planning.


At current production levels, frost resistant food crops could not feed all NZ citizens following a nuclear war and nuclear winter that substantially increased the frost period.

However, this problem could be overcome by increased pre-war production of frost-resistant crops and/or post-war scalability; growing enough frost sensitive crops (ie, in greenhouses or the warmest parts of the country); and/or ensuring continuing production of food derived from livestock fed on frost resistant grasses.

A close analysis of the liquid fuel, agrichemical and seed stock requirements of achieving this is needed.

The NZ Government should conduct a detailed pre-catastrophe analysis on how these issues are optimally addressed. A cooperative non-partisan approach can ensure food security throughout even the worst scenarios. NZ needs a national food security strategy.

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