In case of a nuclear war, strikes on cities and industrial areas would cause firestorms, injecting large amounts of combustion products (soot) into the upper atmosphere. The soot would spread globally and form an umbrella, preventing the sunlight’s energy from reaching Earth. This would cause decadal disruptions in the Earth’s climate. Such an effect is called "nuclear winter".
In the 1980s, there were investigations of nuclear winter impacts on global agricultural production and food availability, but new information now allows researchers to update those estimates. In order to do it, an extensive study was carried out by 11 scientists from the U.S., Canadian, German, Australian, Norwegian, Spanish, and Taiwanese universities. The main results were published in the Nature Food magazine.
Different nuclear war scenarios studied
A war between India and Pakistan, which recently are accumulating more nuclear weapons with higher yield, could produce a stratospheric loading of 5–47 Tg of soot (Tg is a teragram or – 1012 grams). A war between the United States, its allies and Russia, who possess more than 90% of the global nuclear arsenal, could produce more than 150 Tg of soot and a nuclear winter.
The researchers have studied six possible scenarios. Each of them assumes a nuclear war lasting one week with a different number and yield of nuclear weapons used.
The first scenario implies that 5 Tg of soot would be produced from 100 weapons used, while the sixth one predicts 150 Tg from 4,400 weapons.
It should be noted that catastrophic forest fires in Canada in 2017 and Australia in 2019 and 2020 produced 0.3–1 Tg of smoke (0.006–0.02 Tg soot), which was subsequently heated by sunlight and lifted high in the stratosphere. The smoke was transported around the world and lasted for many months.
The scientists emphasized that the impacts in warring nations were likely to be dominated by local problems, such as infrastructure destruction, radioactive contamination, and supply chain disruptions. Therefore, the results of the study apply only to indirect effects from soot injection in remote locations.
The impact of a nuclear war on the production of food
The researchers studied the impact of climate change as a result of a nuclear war on global food production systems on land and in the oceans.
Using climate, crop and fishery models, they calculated calorie production for different food groups. The authors concluded that the climatic impacts would last for about 10 years but would peak in the first few years.
Decrease in the production of crops and fish after a nuclear war
Global average calorie production from the crops the researchers simulated would decrease 7% in years 1–5 after the war even under the smallest scenario. In the 150 Tg soot case, global average calorie production from crops would decrease by around 90% 3–4 years after the nuclear war.
"The changes would induce a catastrophic disruption of global food markets, as even a 7% global yield decline compared with the control simulation would exceed the largest anomaly ever recorded since the beginning of Food and Agricultural Organization (FAO) observational records in 1961," the researchers pointed out.
Fishery would suffer a lesser impact, since the reduction in oceanic net primary productivity is moderate (from 3% in 5 Tg to 37% in 150 Tg). However, marine wild capture fisheries contribute only 0.5% of total calories and 3.5% of global average protein supply. Global calorie supply comes primarily from crop production.
In 2010, FAO reported that 51% of global calorie availability came from cereals, 31% from vegetables, fruit, roots, tubers, and nuts, and 18% from animal and related products, of which fish contributed 7%, with marine wild catch contributing 3%.
Primary conclusions of the study
Even in case of a limited nuclear war, many regions would become unsuitable for agriculture for multiple years. For example, in the 27 Tg case, mid- to high latitudes of the Northern Hemisphere would show reductions in crop calorie production greater than 50%, along with fish catch reductions of 20–30%.
After a large-scale nuclear war (150 Tg soot), most nations would have calorie intake lower than resting energy expenditure. Hence, global starvation would be guaranteed.