Nuclear winter

Recent studies predict that even a medium-scale nuclear war in the northern hemisphere may cause cooling in the mid-latitudes of the southern hemisphere. The impact of such cooling on agriculture depends on the magnitude, duration and starting date of the southern nuclear winter. Cooling in the middle of the growing season (summer) can have serious consequences, whereas cooling during the dormant season (winter) may have little effect. Various temperature reduction schemes are considered. A cooling of 5 deg. C, equivalent to temperatures during the last glacial maximum, dramatically reduces primary production. A spring cooling of 3 deg. C and other seasons of 1 deg. C eliminates yields from many warm temperate crops and lowers grass production. Smaller temperature decreases have less effect. Given the limitations and uncertainties of the models, these scenarios should be treated with caution; but our results show that a northern hemisphere war could significantly affect New Zealand agriculture