Table 1.
Four nuclear war and nuclear winter scenarios considered in this study (adapted from:20).
| Nuclear war and winter scenario | Scale of impact of a nuclear winter | Estimated impact on agricultural production in New Zealand |
|---|---|---|
| No nuclear winter, following a nuclear war in the Northern Hemisphere (Scenario: NW0) | The war in this scenario is assumed to result in no nuclear winter impacts (reflecting persisting uncertainties in the modeling literature30) | Zero from no significant changes to sunlight, temperature, precipitation, and ozone levels |
| Some nuclear winter, following a regional nuclear war (e.g., between India and Pakistan) (NW1) | We used the lower end impact (5 teragram [Tg]) of the estimated 5 to 47 Tg range of stratospheric loading of soot from a nuclear war. This is from a major modeling study published in Nature Food in 2022 by Xia et al.16 | An 8% reduction in major food crops and marine fish* 16 |
| Severe nuclear winter, following a major Northern Hemisphere war (NW2) | We used the impacts from a New Zealand Planning Council study of a 5000 to 6000 megatonne war in July (Northern Hemisphere summer)31. This was assumed to result in a spring temperature reduction in New Zealand of 3 °C, a 2 °C reduction in summer and a 1 °C reduction for another 18 months. Although the relatively high megatonnage of this scale of war may not be particularly realistic in the 2020s – it could still represent the impact of a current-era war with attacks on cities and high levels of stratospheric loading of soot (see the next row). It could also represent a war involving China in the 2030s (since it is expanding its arsenal) | A 28% reduction (mid-point in the estimated 19–36% reduction in pasture growth in year one)** 32 |
| Catastrophic nuclear winter, following a major Northern Hemisphere war (NW3) | We used the highest value (150 Tg) of stratospheric loading of soot used in the work by Xia et al.16. This analysis suggests that cropland solar radiation would be lowest between years 1 and 2 post-war, and take at least 10 years to return to normal. Cropland precipitation would be lowest around year 4 post-war, and also take at least 10 years to return to normal | A 61% reduction in major food crops and marine fish* 16 |
*This study by Xia et al. estimated food energy production for New Zealand as part of a global analysis using data for major food crops (maize, rice, soybean and spring wheat) and marine fish averaged in year two. For modeling parsimony, we used these specific reductions for across-the-board food production, even though grass growth for livestock production may be less impacted than crop production. This 8% reduction value from the Xia et al. 5 Tg scenario compares with a 12% reduction for maize and wheat in year 4 (and a 5% reduction average for years 1–5) in an earlier study (i.e., Jägermeyr et al.: Table S3)15.
**This New Zealand work32 estimated pasture dry matter production impacts from nuclear war for Waikato, Canterbury and Southland regions with reductions in year one ranging from 19 to 36%. For year two the range involved reductions from 11 to 17%. It has also been estimated for New Zealand that a 3 °C decline in temperature would delay the maturity of wheat crops in Canterbury by about 40 days19. This would probably not be a major problem but a 20% decline in solar radiation would result in a probable decline in yield of 15%. Also noted was that in Southland a 3 °C decline in temperature might actually prevent maturation of grain crops19. The impact of the frost-free period would be highly variable around the country. For example, for Ophir (Central Otago) a 1 °C drop in minimum temperature decreases the frost-free period by around 24 days (from 93 days), while for Tauranga it decreases by over 50 days (from around 350 days, albeit these estimates were from the 1980s)32.