International trade would come to a standstill
Xia’s team evaluated data from the Food and Agriculture Organization of the United Nations. The researchers used this to calculate how falling crop yields and reduced fishing after a nuclear war would affect the food available. How many calories were left for each human? The scientists included various criteria in their calculations, such as whether people would continue to raise livestock or whether they would eat some or all of the feed intended for livestock themselves. The scientists also assumed that some of the crops that are processed into biofuels would be processed for humans. You could also try to waste less food. The working group classified the scenario that international trade was idle and countries would no longer export their food as likely. The food security of their own population would then take precedence.
According to Xia, their study is based on many assumptions and simplifications about how the world would react to a nuclear war. But Xia’s team’s results are impressive. Even in the worst-case scenario, a war between India and Pakistan that would release five million tons of soot into the atmosphere, world production of usable calories could fall by 7 percent in the first five years after the war. With 47 million tons of soot, the average global calorie production drops by up to 50 percent. Should a nuclear war break out between the US and Russia, calorie production would drop by 90 percent three to four years after the war.
Countries in the middle and high latitudes would be hit hardest. The cultivation period there is already short. After a nuclear war, however, these regions would cool even more—more than tropical regions. In the UK, for example, far less food would be available than in a country like India, which is at lower latitudes. France, which exports food on a large scale, would get off relatively lightly, since there would be more food for its own population – at least in the scenarios with lower emissions.
The same applies to Australia. Cut off from trade in a nuclear war, the country could focus on growing wheat, which would thrive relatively well there in cooler climates. But large parts of the world would be threatened by hunger.